Service Manual - Red Dot Corporation

Service Manual - Red Dot Corporation
A i r
C o n d i t i o n i n g
S y s t e m
Red Dot
HVAC
Training Manual
Heavy-Duty
Air Conditioning
And Heater
Service
Heavy Duty Air Conditioning and Heating
Service Training Manual
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Copyright Information
Prepared by
HEATERS AND
AIR CONDITIONERS
®
Red Dot Corporation
Heavy Duty Air Conditioning and Heating
Service Training Manual
Published by
HEATERS AND
AIR CONDITIONERS
®
RED DOT CORPORATION 495 Andover Park E. P.O. Box 58270 Seattle WA 98138-1270
RED DOT CORPORATION
Publisher
Red Dot Part No. RD-5-5900-0
Trademarks: The terms CTC™, Binary™, Trinary™, and TWIN TEMP™ are
registered trademarks of Red Dot Corporation. Freon® is a registered trademark of DuPont Corporation. MITYVAC® is a registered trademark of Neward
Enterprises Incorporated.
Disclaimer: The technical information and procedures described in this publication have been obtained from the most reliable sources available. The publisher assumes the data is accurate and current at the time of publication and
does not accept any liability for errors, omissions or the correctness of contents
or procedures described herein.
Copyright: No part of this work may be reproduced or used in any form or by
any means—graphic, recording, taping, or information storage and retrieval
systems—without written permission of the publisher and copyright holder.
Second Edition
Copyright © 1993 by RED DOT CORPORATION—All rights reserved.
Table of Contents
Table of Contents .........................................................1-3
Introduction........................................................... Intro-1
1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Chapter 11
Chapter 12
Chapter
Air Conditioning / Heating Function .......................... 1-1
Overview of System Operation ....................................2-1
Heater Components and Controls ...............................3-1
Air Conditioner Components .......................................4-1
System Controls ...........................................................5-1
Service Tools and Their Use ........................................6-1
Inspection and Maintenance–without gauges ............ 7-1
Troubleshooting & Service Procedures ....................... 8-1
Refrigerants .................................................................9-1
Component Repair or Replacement .......................... 10-1
Typical HVAC Systems and Components ................. 11-1
Retrofitting an R-12 System ......................................12-1
Glossary ........................................................................ i-1
Figure Index ................................................................ ii-1
Subject Index.............................................................. iii-1
Go to Copyright Information
Introduction
This manual has been designed and written for your use. Take your time
reading it. Study the illustrations, charts and photos. Figure 1 shows a typical
HVAC system (heating, ventilating, air conditioning) installed.
The illustration is cut away so you can see component locations. All of the
main components are labeled, connected together and positioned approximately as they appear in the vehicle. These components may differ from one
cab to another. There could be other system devices for safety or perhaps
sleeper cab comfort.
Figure 1
The illustration shows a
typical HVAC system with
in-cab components mounted
on the fire wall. The main
system components are
noted in this illustration.
DEFROSTER DUCT
BLOWER AND
MOTOR
AC/HEATER
VENTS
EVAPORATOR
COIL
REFRIGERANT
SUCTION LINE
REFRIGERANT
DISCHARGE LINE
COMPRESSOR
HEATER CORE
MAGNETIC
CLUTCH
EXPANSION
VALVE (TXV)
COOLANT
LINE (RETURN)
COOLANT
(WATER) VALVE
COOLANT LINE
SUPPLY
SIGHT GLASS
BINARY™
OR TRINARY™
SWITCH
RECEIVERDRIER
REFRIGERANT
LIQUID LINES
Go to Table of Contents - Index
WATER PUMP
FAN CLUTCH
RADIATOR MOUNTED
CONDENSER
OR GRILLDENSER
Intro-1
Introduction
Figure 2
CONDENSER WITH
RECEIVER DRIER
Typical off-road installation.
REFRIGERANT DISCHARGE LINE
A/C VENTS
MAGNETIC CLUTCH
COMPRESSOR
REFRIGERANT SUCTION LINE
BLOWER AND MOTOR
REFRIGERANT LIQUID LINE
EVAPORATOR WITH
EXPANSION BLOCK
AND THERMOSTAT
The Table of Contents lists the chapters and gives you their page locations.
There are two separate indexes at the back of the manual. The Figure Index
describes each figure with its number and page location. The Subject Index will
help you locate each subject covered in the manual.
Each chapter begins by listing the main topics you will want to learn and
remember. Key points are repeated for your review at the close of most chapters. The illustrations are explained and parts are labeled where necessary for
easy identification. You should feel free to make notes in this manual and
underline or circle anything that is important to you.
Our purpose is to give you knowledge, and confidence in your ability to work on
heavy duty air conditioning and heating systems. Your working speed and
trouble shooting skills will improve with experience.
The systems we cover here for heavy duty heating and air conditioning are
easy to understand. They are a little different from most other mechanical
systems, because they are closed (sealed) systems and have to function under
pressure to work properly. You will become familiar with a few of nature’s laws
that most of us take for granted. These concern how heat really works and the
effects of pressure under different conditions. There is a Glossary of Terms at
the back of this manual. The Glossary explains words that may be new or not
clear to you.
Safety is very important to all of us. Chapter 6, page 6-10, reviews safety
procedures in detail. We also use “NOTES,” “CAUTIONS,” and “WARNINGS”
in this manual. Any time you see a CAUTION, we are talking about a situation
that could lead to equipment damage or failure. A “WARNING” specifically
warns you about the potential danger to humans (the operator, the
serviceperson) when equipment use or instructions are not properly followed.
You will be handling engine coolant and air conditioner refrigerant in your
work. Both are chemicals and can be unsafe to work with when used incorrectly.
Intro-2
Go to Start of Introduction - Table of Contents - Index
Introduction
The Clean Air Act, passed in 1992, specifies that anyone who works on vehicle
air conditioning systems must be certified as proof of their training. Organizations such as the Mobile Air Conditioning Society (MACS) and the National
Institute for Automotive Service Excellence (ASE) are approved by the Environmental Protection Agency (EPA) as organizations having approved independent testing and certification programs. At the time of this writing, others are
being considered. For more information, please contact your regional EPA
office.
Now it is time for the details, the things that make these systems work. Take
a few moments now to study Figure 1. Familiarize yourself with the component
names and then move on to the chapters that follow. All the details are covered
there.
Go to Start of Introduction - Table of Contents - Index
Intro-3
1
Chapter
Click on any of these
subject headings to go
directly to the page
Air Conditioning /
Heating Function
• Cab Environment
• Heat Sources
• Heat Movement
• Heat Measurement
• Heat Relationships
• Changes of State
• Heat Movement During Changes of State
• Air Conditioner/Heater Functions
• Chapter Review
Cab Environment
The purpose of a heater/air conditioner system is to keep the driver comfortable. You are already familiar with your car system—if you are cold, you turn
on the heater. On a warm summer day, you either turn on the air conditioning
system or open the windows. Most people feel comfortable when they are
surrounded by air that is 70 to 80 degrees. Because truck drivers and heavyduty vehicle operators are usually in their cabs for long periods of time, the cab
temperature is very important to their comfort.
Truck and off-road cabs are hard to heat and cool. They have a large glass
area and are not always well insulated. Hot and cold weather directly affect the
temperature inside the cab. This means that any air conditioner/heater system
must have the capacity to do a lot of cooling or heating. Figure 1-1 shows the
temperature range inside a cab.
Figure 1-1
Inside cab environment
A 70 to 80 degree temperature range and modest
humidity level is best for
most people. The heater/AC
system should reach and
remain within this temperature range after a few minutes of operation.
70°
80°
120°
32°
CAB
TEMPERATURE
RANGE
0°
Go to Table of Contents - Index
1-1
Chapter 1 – Air Conditioning / Heating Function
The ideal cab environment has a modest humidity level. The temperature
should reach and then remain in the ideal range, 70 to 80 degrees. The cab
should reach this temperature range after a few minutes of system operation
with the windows closed. Air within the cab should be exchanged every few
minutes to remove smoke, products of respiration and other odors.
Most air conditioner systems cycle on and off by the action of thermostatic
and/or pressure sensitive devices. It is this on-off, open- closed action that
maintains a comfortable temperature range for the driver and any passengers.
Heat Sources
Heat is a form of energy. The control of heat energy is what air conditioning and
heating is all about. In summer a vehicle cab absorbs heat from various sources
such as the sun, the road surface, engine, transmission, hot outside air, and
even the people in the cab. In winter the cab looses heat to the cold outside air.
Figure 1-2 illustrates a truck cab in two situations—operating in summer
and winter.
Figure 1-2
SUMMER
100°
H
H
WINTER
20°
H
H
H
H
H
This drawing shows how
heat moves; one of nature’s
laws. Heat always moves
from a warm to a cool
area—heat flows into the
cab in hot weather and
flows out in cold weather.
H
H
H
70°
80°
32° CAB 120°
COMFORT
0° RANGE
H
H
H
Heat Movement
Heat always moves from a warm area to a cooler one until both areas are at the
same temperature. You know from experience that on a cold day, when you
drive somewhere with the heater on, your vehicle is comfortable. But if you
park it for awhile with the engine off, the cab and the engine will both
eventually reach the same temperature as the outside air. Figure 1-3 illustrates this in a parked vehicle.
1-2
Go to Chapter Start - Table of Contents - Index
Heat Movement
Figure 1-3
WINTER
20°
The inside cab temperature
will be the same or higher
than the outside temperature when parked for awhile
with all systems turned off.
SUMMER
100°
80°
100°
32° CAB 120°
TEMP
20°
0°
70°
Figure 1-4 displays the key components in the HVAC system. The arrows show
the direction of refrigerant flow in the system.
Figure 1-4
We have used arrows to
show you the direction of
refrigerant and engine
coolant flow in the system.
The key system components
are named. The air conditioner evaporator coil and
condenser, and the heater
core, are the main points of
heat transfer.
REFRIGERANT
SUCTION LINE
EVAPORATOR
COMPRESSOR
MOVES HEAT ENERGY
IN REFIGERANT
HEATER CORE
REFRIGERANT
DISCHARGE LINE
COOLANT LINE
(PRESSURE)
COOLANT LINE
(RETURN)
EXPANSION VALVE
COOLANT
(WATER) VALVE
WATER PUMP
MOVES HEAT ENERGY
IN THE COOLANT
CONDENSER
REFRIGERANT
LIQUID LINES
Go to Chapter Start - Table of Contents - Index
1-3
Chapter 1 – Air Conditioning / Heating Function
Figure 1-5
Note the heater core and air
conditioner condenser in
this illustration. Both serve
these systems as the main
point of heat energy radiation. The heater radiates
heat to warm the vehicle
occupants. The condenser
radiates heat from the
refrigerant to the air outside the cab.
H H
H
HEATER
GIVES UP
HEAT ENERGY
TO AIR IN CAB
H
CONDENSER
GIVES UP HEAT
ENERGY TO
OUTSIDE ENERGY
H
Heat Measurement
There are two ways to measure heat—heat intensity in degrees Fahrenheit, or
degrees Celsius, and heat quantity in British thermal units (BTU’s).
Heat Intensity
We measure heat intensity (how hot something is) as temperature in
degrees Fahrenheit (or in the metric form, degrees Celsius). In your
service work on HVAC systems, you may use a dial type thermometer to
measure heat intensity. Figure 1-6 illustrates a typical dial type thermometer. It’s an ideal tool for measuring heat intensity as you work to
check out or troubleshoot these HVAC systems. The chart in Figure 1-7
converts degrees Fahrenheit to degrees Celsius.
20
NEEDLE MEASURES HEAT ENERGY
40 60
Figure 1-6
80
10
0
0
-2
12
0
TEMPERATURE SENSING PROBE
1-4
0
14
-4
0
D
FA EG
HR RE
EN ES
HE
IT
0
16
0
18
0
A typical dial type thermometer has a probe on it
that extends about six
inches. The probe senses
and indicates the temperature in hard to reach
places—such as in air distribution ducts.
Go to Chapter Start - Table of Contents - Index
Heat Measurement
Figure 1-7
Fahrenheit/Celsius Conversion
F°
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
C°
-1
4
10
16
21
27
32
38
43
49
54
60
66
71
77
82
88
F°
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
C°
93
99
104
110
116
121
127
132
138
143
149
154
160
166
171
177
Heat Quantity
Another measurement is heat quantity, or how much heat there is. British
thermal units or BTU’s are the accepted unit for measuring heat quantity.
For example, at sea level one BTU of heat energy raises the temperature
of one pound of water one degree Fahrenheit. If we keep adding BTU’s to
that pound of water, we will get to the boiling point of 212 degrees. At that
point the temperature will normally stop going up even if we continue to
add heat (BTU’s).
If you want the pound of water to change to steam (from a liquid to a vapor),
you have to add a lot of BTU’s. In fact you would add 970 BTU’s of heat energy
before the entire pound of water would change to steam. You would only add
180 BTU’s to take that pound of water from 32 degrees to the boiling point of
212. Look at the three kettle drawings in Figure 1-8 for a moment. They show
what happens to water when heat quantity is added. Review the drawings in
this illustration from left to right.
212°
Figure 1-8
In this illustration a pound
of water changes to vapor
when 970 BTU’s of heat
energy are added to it. This
change in water is called a
“change of state”. Note
that the temperature in the
middle picture and the one
on the right remains the
same, 212 degrees.
212°
1 POUND
OF WATER
212°
+
1
BTU
=
WATER
BOILS
212°
+
970
BTU’S
=
VAPOR
(STEAM)
Here is the interesting part. When you add 970 BTU’s to change the water to
steam, the temperature stays at 212 degrees. All the BTU’s of heat energy went
into the steam. It took 970 BTU’s of energy to cause the water to change. If you
were to cool the steam back to water again, the 970 BTU’s of heat energy would
be given up to the air. The important thing about the example and illustrations
in Figure 1-8, is the large amount of heat it takes to change a substance like
water from one state to another. In fact, this is one of the reasons HVAC
systems are able to handle heat effectively. To put it another way, when you can
control a “change of state” you can move a lot of heat.
The heavy duty HVAC systems you will be working on are designed to move
heat energy quickly. Engine coolant and refrigerant are used to carry heat
energy into or out of the cab. Both of these liquids are good at absorbing and
giving off BTU’s of heat in the vehicle cab to make us comfortable.
Go to Chapter Start - Table of Contents - Index
1-5
Chapter 1 – Air Conditioning / Heating Function
Heat Relationships
Relative humidity plays an important part in our comfort. So does air movement. The relative humidity is a measure of the moisture in the air. Air
movement is a measure of the speed or velocity of air as it moves. We use CFM’s
or Cubic Feet per Minute as a measure of air movement. As they operate, truck
HVAC systems remove humidity or moisture and circulate the air around us to
keep the cab occupants comfortable.
Changes of State
We talked about “change of state” when we mentioned earlier that 970 BTU’s of
heat energy were needed to change a pound of water into vapor. We use water
in our example because it is familiar to all of us. In AC systems the refrigerant
is used instead of water. It evaporates and condenses (changes state) in the
system almost continuously. It is this action that makes an air conditioner cool
the cab and its occupants. A “change of state” works for us by moving large
amounts of heat energy fast, under the right conditions.
Heat Movement During Changes of State
Evaporation and condensation both take place inside the air conditioning
system. When either of these conditions occur, a lot of heat moves. We use
refrigerant because its temperatures of vaporization and condensation are
nearly optimum for this application. Using the familiar 20 pound refrigerant
cans, Figure 1-9 shows the effect of a “change of state” on R-12. You can see how
fast a change in pressure in the can changes the temperature of the refrigerant.
WARNING
Refrigerant can be dangerous if released as shown
below. These drawings are for illustration purposes
only—to show “change of state”.
VALVE CLOSED
VALVE CRACKED OPEN
VAPOR
1-6
Figure 1-9
VALVE OPEN WIDE
VAPOR AT -21.6° F (0 PSI)
70.1 PSI
46.6 PSI
10.0 PSI
70° F
50° F
2° F
AIR TEMPERATURE
70° F OUTSIDE
OF CAN
In these drawings the dispensing valve is used to
release pressure inside the
cans. Note that R-12 boils at
a temperature of -21.6
degrees Fahrenheit, compared to water at 212 degrees Fahrenheit.
Go to Chapter Start - Table of Contents - Index
Air Conditioner/Heater Functions
In an air conditioner, the refrigerant is trapped inside a closed system and
circulates under pressure. When we put any substance under pressure, the
pressure changes the way it acts. We can control the amount of pressure at
different locations within an air conditioner in order to change the temperature
level wherever a “change of state” occurs. Thus we use “change of state”, one of
nature’s laws, to add or subtract heat in large quantities from a substance—
fast! Figure 1-10 shows the points where “changes of state” occur in the truck
AC system. Refrigerant, in this case R-12, evaporates inside the evaporator coil
and condenses inside the condenser.
Under normal operating conditions there is no change of state within the
heater system.
Figure 1-10
This illustration highlights
the evaporator and condenser in a cutaway view of
the typical HVAC system.
The R-12 changes from
liquid to vapor or gas at the
evaporator, and back to a
liquid again at the condenser.
H
COMPRESSOR
RAISES PRESSURE
FROM 20-40 PSI
TO 150-180 PSI
H
LIQUID TO GAS
CHANGE OF STATE
IN EVAPORATOR
TYPICAL LOW SIDE
PRESURE IS 20-40 PSI
H
H
EXPANSION VALVE:
PRESSURE DROPS HERE
FROM 150-180 PSI
TO 20-40 PSI
H
GAS TO LIQUID
CHANGE OF STATE
IN CONDENSER
TYPICAL HIGH SIDE
PRESSURE IS
150-180 PSI
Air Conditioner/Heater Functions — What They Do
These systems are designed to provide comfort to the cab occupants as quickly
as possible. The systems change the cab temperature and maintain it. They use
refrigerant and engine coolant (anti-freeze) to move heat energy. The refrigerant in air conditioning systems removes heat from the cab. The engine coolant
takes heat from the engine and transfers some of it to the cab through the
heater core.
HVAC systems also control humidity or moisture as the air in the cab is
circulated. The system components may act together or independently, switching on or off to meet present control requirements. The driver or passengers can
change system control settings to meet their own personal comfort needs. The
controls can affect temperature and humidity levels, air direction and speed
(CFM). System controls are described in Chapters 3 (heater) and 4 (air conditioner) of this manual, and explained in more detail in Chapter 5.
It is important to remember that all systems are designed to maintain a
temperature range. This range takes care of variations in outside temperature
which cause heat gain when it is hot, or heat loss when it is cold.
Go to Chapter Start - Table of Contents - Index
1-7
Chapter 1 – Air Conditioning / Heating Function
Chapter Review
The following topics were discussed in this chapter:
• The ideal in cab environment for most people is 70 to 80
degrees Fahrenheit, with a modest humidity level and adequate air circulation.
• Heavy vehicle cabs are hard to cool or to heat because of the
weather, minimal insulation, and the large glass area of the
cab. In summer the cab picks up heat from the sun, road,
engine, transmission, and body heat from the occupants. An
operator who spends long periods in the cab can be more
critical of the cab environment.
• We measure heat (energy) two ways—in degrees Fahrenheit
or Celsius, and BTU’s. Degrees measure heat intensity.
BTU’s measure heat quantity.
• One of nature’s laws is that heat (BTU’s) always moves from
a hot area to a cooler area until both are at the same temperature (intensity) in degrees Fahrenheit.
• Another of nature’s laws is that a “change of state” accounts
for the movement of a lot of heat. If the change of state
happens fast, the heat moves fast. When refrigerant changes
state, it can give off or absorb large quantities of heat
(BTU’s).
1-8
Go to Chapter Start - Table of Contents - Index
Chapter
2
Click on any of these
subject headings to go
directly to the page
Overview of System Operation
• Truck and Heavy Equipment Systems
• Air Conditioner-System Operation
• Heater System Operation
• Environmental Effects on System Operation
• Chapter Review
Truck and Heavy Equipment Systems
A variety of HVAC systems are in use today, some old and some new. There are:
• Vehicle manufacturer installed systems
• Owner specified systems
• Add-on systems
• Retrofit systems
The system components come in different colors, shapes, and sizes. They may
be mounted in or on the cab in varied locations. Owners or fleet maintenance
people can modify systems by adding controls, auxiliary units or ducts. Major
components are sometimes replaced due to damage or failure. All systems
were, at least originally, designed and installed to meet the needs of an
operator. Figure 2-1 includes illustrations of various AC and Heater systems.
They illustrate system advantages and disadvantages explained in the paragraphs that follow.
The HVAC system includes both heater and air conditioner components,
usually a common control, and air ducts. The system cools the cab by removing
heat energy. It removes moisture from damp air in the cab and adds fresh
outside air to the cab. In this way, the operator can work comfortably in all
kinds of weather.
A sleeper unit, built in or added on, increases the air volumes in the cab. The
air conditioner or heater must circulate and cool or heat a larger amount of air.
This is accomplished by routing ducts and controls to the sleeper compartment
as part of system design. Components may be increased in size to handle the
larger cab air volume. A bigger heater core, air conditioning evaporator coil,
condenser, blower or fan may be included. Often, on long haul trucks, auxiliary
air conditioning and heater components and controls are added. The objective
remains the same, to move heat energy and maintain occupant comfort.
Go to Table of Contents - Index
2-1
Chapter 2 – System Operation
Figure 2-1
D
C
These illustrations show a
basic heater, HVAC system,
the combo system with
sleeper unit, add on AC roof
top and in cab units, roof
mounted condenser and
auxiliary units.
ADD ON AC FOR INCAB MOUNTING TO
BACKWALL
AC/HEATER IN DASH MOUNT COMBO
SYSTEM WITH SLEEPER UNIT
E
(X)
UNIVERSAL AUXILIARY
HEATER (DEFROSTER OPTIONAL)
G
F
B CUSTOM DESIGN AC/
HEATER COMBO UNIT
INTEGRATES WITH EXISTING
DASH COMPONENTS.
NOTE POSITION OF VENT
(X) TO DEFROST
WINDSHIELD AND UP
FRONT SYSTEM CONTROLS
C
B
E
A
NOTE LETTERS IN
CIRCLES SHOW THE
MOUNTING
D LOCATION FOR THE
SYSTEMS
ILLUSTRATED A
THROUGH G
F
ROOF MOUNTED AIR
CONDITIONER WITH
OVERHEAD AIR
DIFFUSERS AND
CONTROLS
C
G REMOTE MOUNTED
CONDENSER WITH
RECEIVER-DRIER AND
DUAL FANS & MOTORS
A HEATER–FLOOR OR
BULKHEAD MOUNTING
By law, all trucks have a heater/defroster as part of the standard equipment.
When there is a reason to add air conditioning, there are options to meet
different needs. The available space in the cab, operating environment, and
owner preference can all play a part in the type of AC unit selected. You will
probably encounter roof-mounted and in-cab add on systems, and even systems
where the condenser is mounted on the roof and the evaporator is attached to
the back panel or mounted under the dash. In cooler climates you may come
across a cab with two heaters, the original and an auxiliary unit.
Air Conditioner—System Operation
We have described the movement of heat energy and basic HVAC system
function in Chapter 1. Now we will go into some detail on how an air conditioner operates. The system is sealed to keep out air and moisture. To operate
properly, the inside of the system contains a measured amount of refrigerant
and special refrigerant oil that keeps the system lubricated. Figure 2-2 is an
illustration of system components without the cab outline, in-cab controls,
component housing, and air ducts or vents. Please study it for a moment. Note
the information printed next to each component. Remember that the components may be positioned and attached to the truck in various locations.
2-2
Go to Chapter Start - Table of Contents - Index
Air Conditioner—System Operation
The following AC components are discussed in detail in this section:
1. Compressor/Clutch Assembly
2. Condenser
3. Receiver-Drier
4. Expansion Valve
5. Evaporator Coil
Figure 2-2
Air Conditioner components
are connected together to
illustrate system operation.
The components shown are
not to scale. The refrigerant
and refrigerant oil are clear
in color and not visible in
this drawing. The small
arrows inside the components and connecting hoses
show the direction of refrigerant flow (refrigerant
circuit).
HOT HIGH
PRESSURE GAS
LOW PRESSURE GAS
[SUCTION SIDE]
COLD LOW PRESSURE GAS
OUTSIDE AIR FLOW
EXPANSION
VALVE
CAB AIR
FLOW
COMPRESSOR
METERED
REFRIGERANT
CONDENSER
HIGH PRESSURE
LIQUID
EVAPORATOR
RECEIVER-DRIER
THERMOSTAT
1. Compressor/Clutch Assembly
The compressor/clutch assembly is the heart of the system. When the
clutch is engaged, the compressor pumps refrigerant and oil around the
system. It raises the temperature and pressure of the refrigerant gas, and
forces it to the condenser where it changes state and becomes a liquid. The
compressor also sucks the vaporized refrigerant out of the evaporator and
back inside itself in the form of gas. One way valves inside the compressor
separate the compressed gas (high pressure) side of the system from the
suction (low pressure) side. Figure 2-3 shows a cutaway view of a compressor with the high and low pressure sides noted.
Go to Chapter Start - Table of Contents - Index
2-3
,,
,,
,,
,,
,,
,,
Chapter 2 – System Operation
INLET
OUTLET
PISTON ON
DOWNSTROKE
AND
UPSTROKE
DOWN
INLET LOW PRESSURE – ON DOWNSTROKE
PISTON SUCKS REFRIGERANT GAS THROUGH
OPEN VALVE
Figure 2-3
The compressor inlet is low
pressure and the outlet is
high pressure. The reed
valves are one way. They
open to allow refrigerant
gas to enter the compressor
on the down stroke and exit
on the upstroke. Note the
open valves in the illustrations.
UP
OUTLET HIGH PRESSURE –ON UPSTROKE VALVE
FORCED OPEN AND HOT REFRIGERANT GAS IS
FORCED INTO HIGH SIDE OF SYSTEM
The clutch is mounted on the shaft of the compressor and is engaged by
electromagnetic action. Part of the clutch assembly is an electromagnetic
wire coil. The coil is energized through a thermostat that senses the
temperature in the evaporator coil. If the evaporator is too warm the
electrical contacts close and allows power to flow to the clutch. The
compressor shaft is engaged and moves the refrigerant around inside the
system. Figure 2-4 is a cutaway view of the clutch mounted on the
compressor.
Figure 2-4
,,
,,
,,
,,,
,,,
REED VALVE
CLUTCH COIL LEAD
WIRE TO EVAPORATOR
THERMOSTATIC
SWITCH
The clutch shown here has
its electromagnetic coil
mounted on the compressor
body. When the coil is energized, magnetic force pulls
the clutch drive plate into
the pulley. This action locks
the pulley to the compressor
drive shaft and drives the
compressor.
MAGNETIC
CLUTCH-COIL
COMPRESSOR
CLUTCH
2. Condenser
The refrigerant gas leaves the compressor and moves through a high
pressure hose to the condenser. Inside the condenser the gas “changes
state” and becomes a liquid. It is still hot and under pressure. Remember
in Chapter 1 when we talked about water at 212 degrees Fahrenheit?
Heat energy was involved in the “change of state,” but the temperature
did not change. The same kind of action happens inside the AC system.
The refrigerant gas gives up a lot of heat energy to the outside air as it
“changes state” in the condenser. Figure 2-5 illustrates a condenser. Air
moving through the condenser absorbs heat from the refrigerant. The
amount of air flow through the condenser is the major factor in how well
the condenser functions.
2-4
Go to Chapter Start - Table of Contents - Index
Air Conditioner – System Operation
Figure 2-5
As the refrigerant gas
moves through the tubing
coil from top to bottom, it
condenses (changes state)
into a liquid. For ease of
installation, condenser
fittings are often routed
close together.
OUTSIDE AIR
FLOW
HOT HIGH
PRESSURE GAS
(IN)
CONDENSER
HIGH PRESSURE LIQUID
(OUT)
3. Receiver-Drier
The liquid refrigerant continues to move inside the system, out of the
condenser through a tube or hose to the receiver-drier. The receiver-drier
serves as a small storage tank and filter for the refrigerant. It is also a
good location to mount pressure switches and often contains a sight glass
(small window) used to view activity inside the system. The receiver-drier,
Figure 2-6, also separates gas (bubbles) from the liquid with a pick-up
tube as shown in this illustration. Some receiver-driers have a spring to
preload the desiccant pack.
Figure 2-6
SIGHT GLASS
This cutaway view of a
receiver-drier shows the
filter elements, inlet, outlet
and refrigerant path. The
sight glass is a small window into the system used in
diagnosis and when adding
refrigerant (charging the
system).
INLET
OUTLET
STORAGE
SCREEN
FILTER PAD
MOLECULAR SIEVE
(DESICCANT)
FILTER PAD
SCREEN
PICKUP TUBE
RECEIVER-DRIER
Go to Chapter Start - Table of Contents - Index
2-5
Chapter 2 – System Operation
4. Expansion Valve (Refrigerant Metering Device)
When refrigerant moves from the receiver-drier, it travels through another high pressure hose to a metering device at the inlet of the evaporator coil. The metering device can be an expansion valve, an expansion
tube or a combination (multiple function) valve. Between the compressor
and this point inside the system, the pressure is high and can range from
150 to 250 pounds per square inch. The expansion valve (TXV) is closely
connected to the evaporator. A diaphragm opens the valve by exerting
pressure on the spring. Pressure comes from gas inside the diaphragm
housing on top of the valve and in the sealed sensing bulb. The sensing
tube is located in the outlet of the evaporator and picks up heat from
warm refrigerant leaving the evaporator. The gas in the valve diaphragm
housing and sensing tube expands when it gets warmer and forces the
expansion valve open at the metering orifice.
,,
,,
,,
,
,, ,,
VALVE DIAPHRAGM
INTERNAL
EQUALIZATION
PASSAGE
Figure 2-7
This block type expansion
valve cutaway view will give
you a better idea how these
valves work. Spring pressure holds the valve closed.
SEALED SENSING BULB
DISCHARGE FROM
EVAPORATOR
OUTLET TO
COMPRESSOR
OPERATING
PIN
OUTLET TO
EVAPORATOR
INLET FROM
RECEIVER DRIER
WHEN OPERATING,
PIN PUSHES BALL
AWAY FROM BALL
SEAT, REFRIGERANT
BLEEDS INTO
EVAPORATOR
HIGH PRESSURE LIQUID
METERING ORIFICE
VALVE SPRING
5. Evaporator Coil
The expansion valve or other type of metering device bleeds high pressure
refrigerant into the evaporator coil, where the pressure is low. The refrigerant expands rapidly in this low pressure environment. When it expands
it “changes state”. The sudden drop in pressure brings the refrigerant
temperature down quickly inside the evaporator coil. Figure 2-8 shows an
evaporator coil and thermostat. Refrigerant is sprayed into the evaporator by the high side pressure when the expansion valve opens. The
refrigerant absorbs heat from the air when the blower forces the air
through the fins. When the thermostat probe senses the upper limit of the
thermostat heat setting, a circuit closes. The compressor clutch engages
and the compressor operates and moves more refrigerant to the high side
of the system.
2-6
Go to Chapter Start - Table of Contents - Index
Air Conditioner – System Operation
Figure 2-8
The evaporator coil as
shown is of fin and tube
construction. The thermostat probe is positioned in
between the evaporator fins
and senses the temperature.
THERMOSTAT
Note:
Moisture in the air (humidity) condenses on the fins
of the evaporator as water droplets which drain out of
the evaporator through a drain hose. This action dehumidifies the air in the cab as part of system operation, and contributes to operator comfort.
Cab air forced across the evaporator coil gives up heat energy to the cold
refrigerant inside the coil. The cooled air circulates in the cab for occupant
comfort. Refrigerant continues to expand and absorb heat energy in the
evaporator coil. Refrigerant changes from liquid to gas before it leaves the
evaporator on the way back to the compressor. The refrigerant gas moves
to the compressor through a low pressure (suction) hose. When the compressor is operating, it sucks the refrigerant gas back inside, compressing
and raising its temperature and pressure.
Some of AC system operation is controlled by the operator, and some is automatic. The operator can turn the system on and off, regulate the air velocity
with the blower control, and in some designs adjust the thermostat control. The
system and component operating range settings automatically cycle the clutch
on and off. The operation of the expansion valve or other refrigerant metering
device at the inlet to the evaporator is automatic.
Individual system features may differ, but the basic system function remains the same. Variations in components and controls are described in Chapters 4 and 5. The engine provides the power for both air conditioner and heater
operation. It drives the AC compressor and the cooling system water pump.
Engine RPM affects the efficiency of both the heater and air conditioner. The
slower the engine RPM, the less capacity a heater or AC system will have.
WARNING
When an AC system is operating, the high pressure side
components, fittings and high pressure lines or hoses can
be hot enough to burn your skin if you touch them. This
includes the compressor, clutch, hoses, condenser, receiver-drier, and any control devices or metal tubing. The
low pressure side will be cool to the touch. In operation
the AC system is under load and high side pressures
normally range between 150 and 250 pounds per square
inch for R-12 and higher for some other refrigerants.
Go to Chapter Start - Table of Contents - Index
2-7
Chapter 2 – System Operation
Heater System Operation
Heater and air conditioner systems both have the same basic function of
moving heat. They take advantage of nature’s laws where heat energy always
moves from a warmer to a cooler area. In a heater system there is no “change of
state” involved in system operation. The system is sealed and operates under
pressure, but the pressure is low when compared to an air conditioner.
A heater system uses the engine coolant to carry excess heat energy to the
cab air. The heart of the system is the water pump. The water pump forces hot
coolant through a hose from the engine block and through the heater core. The
coolant is returned to the engine cooling system either at the suction side of the
water pump or to the radiator.
A control cable, attached to a water valve between the water pump and the
heater inlet, is used to control the flow of coolant to the heater. The heater fan
or blower forces cab air through the heater core where heat energy moves from
the engine coolant to the air in the cab. Figure 2-9 illustrates the main heater
system components. In-cab controls, component housing and air vents are not
shown.
The following heater components are discussed in detail in this section:
1. Heater Core
2. Water Valves
3. Defrosters and Ducts
4. Blowers and Fans
Figure 2-9
This view of a heater system
shows the main components
and how they are connected.
DEFROSTER DUCT
CABLE CONTROL
FROM DASH TO
WATER VALVE
HEATER CORE
COOLANT LINE
TO HEATER (PRESSURE)
BLOWER AND
MOTOR
COOLANT LINE
(RETURN)
COOLANT (WATER)
VALVE
FAN CLUTCH
WATER PUMP
Additional heater controls, ducts, air vents, blend-air doors, temperature regulating devices and auxiliary heaters may be installed as part of a heater
system. These may be air, vacuum, electrical or mechanically operated.
2-8
Go to Chapter Start - Table of Contents - Index
Environmental Effects
1. Heater Core
Heater cores are like small radiators. The fin and tube construction is
designed to route coolant flow for the best possible heat energy transfer
from coolant to cab air. Hoses from and to the engine are connected to the
core with clamps. The core outlet may be larger or the same size as the
inlet.
2. Water Valves
Water valves may be cable, vacuum or air controlled. The valve can be
either open, closed or set part way open. Some valves have a bypass
design to return coolant to the engine. Most are manually controlled
although electronic systems are now being installed.
3. Defrosters and Ducts
Defrosting is accomplished by directing heated dry air through ducts to
the windshield. The heater system serves the dual purpose of defrosting
and heating. Controls are used to route the air flow to the windshield and
occupant areas by opening and closing duct doors. Controls may be
manual, air or vacuum.
Many vehicles use a “defrost interlock” system which utilizes the air
conditioner to dry the defrost air and clear the cab windows more quickly.
4. Blowers and Fans
Blowers or fans are used in the system to move cab air through the heater
core and evaporator. Air can be pushed or pulled through the core depending on system design. Blower or fan speed is usually selected by the
operator.
Environmental Effects on System Operation
The environment outside the cab involves more than the weather. It may be hot
and humid or cold and dry. That is only part of the condition the HVAC system
must handle to maintain an ideal comfort range. A truck can be at idle, in
traffic or moving along for hours on the Interstate at 65 M.P.H. The load
condition on a trip can include going out full, coming home empty, or driving
across the Rockies or Kansas plains during the day or night. The truck color
and shape, the windows and angle of the sun are all variables that can increase
or decrease the “load” on the system. The following are a few examples of
environmental effect:
• A black cab-over (COE) with a dark color interior will be
more difficult to cool than the same vehicle with white paint
and a light colored interior. The black cab picks up and holds
the radiant heat from the sun more easily than the white one.
• In Florida or Houston the humidity in mid summer can be
very high with the temperature in the high 90’s or low 100’s.
The AC unit must remove a lot of moisture from the air in the
cab as the air moves through the evaporator fins. The more
moisture on the fins, the less effective the transfer of heat is
to the refrigerant inside the evaporator coil.
Go to Chapter Start - Table of Contents - Index
2-9
Chapter 2 – System Operation
• On a cold day the temperature can drop below zero. The
engine may run cooler so the engine coolant is cooler when it
circulates through the heater. The heat in the cab moves out
of the cab faster (remember heat always moves to a cooler
area until both are the same temperature—nature’s law). To
maintain cab comfort you have to increase the flow of coolant
through the heater, increase coolant temperature, and/or
move more air through the heater core.
• On a hot day, an off-road vehicle experiences cooling at a
slower rate than an on-road vehicle. This is a result of high
sun-load, large window area and often less insulation.
It is important for you to keep environmental effects in mind when you are
servicing or diagnosing heater or air conditioner systems. If you work in
Denver the altitude will affect system function and pressure. In Houston the
heat and humidity may lower heat transfer to the air at the condenser and
increase system operating pressures.
Chapter Review
• HVAC systems range from simple cab heaters to multi-function
combination systems. The multi-function system can heat and
cool the cab and sleeper unit, and have separate auxiliary
components and controls for driver and passenger comfort.
• Both heater (engine) coolant and air conditioner refrigerant
circulate inside sealed, pressurized systems. The normal air
conditioner operating pressure ranges from 150 to 250 pounds
per square inch, sometimes higher with a different refrigerant.
• Air conditioners have a high and a low pressure side within the
system. The compressor is the starting point of the high side.
Pressure drops at the expansion valve opening to the evaporator.
• The basic components of an AC system are the compressorclutch assembly, high pressure lines, condenser, receiver-drier,
expansion valve, evaporator, thermostat, blower assembly, and
suction lines. There may be other controls installed for more
complex systems.
• The basic components of a heater system are the inlet and outlet
hoses, a water valve and valve control, heater core and fan or blower
assembly. There may be other controls for more complex systems.
• An air conditioner system uses the “change of state” of refrigerant inside the system to move heat from the cab air to the
outside air. Refrigerant changes from a gas to a liquid in the
condenser, and back to a gas in the evaporator.
• A heater system uses the heat from the engine, carried to the
heater core by the action of the water pump, to warm the air in
the cab. There is no change of state within the heater system.
• Environmental conditions affect how both heaters and air conditioners work. Weather, driving conditions, color of the vehicle are
factors. All contribute to heat gain or loss inside a cab and how
much heat energy must be moved to maintain occupant comfort.
2-10
Go to Chapter Start - Table of Contents - Index
Chapter
3
Click on any of these
subject headings to go
directly to the page
Heater Components
and Controls
• Engine Coolant or Anti-freeze
• Cooling System Thermostat and Radiator Pressure Cap
• Water Pump
• Heater Components and Controls
• Chapter Review
Engine Coolant or Anti-freeze
Ethylene glycol-type coolant (anti-freeze) is mixed with water and used in most
vehicle cooling systems today. Additives in the coolant formula lubricate the
water pump, reduce the chance of rust or corrosion, and prevent foaming.
Although it is often called permanent anti-freeze, the additives break down in
time and loose their protective qualities. For this reason coolant should be
changed at regular intervals. Five main reasons to use coolant in the engine
are:
1. It has a much lower freezing point than water.
2. It has a higher boiling point than water.
3. It is inexpensive.
4. It prevents corrosion for a reasonable period of time.
5. It absorbs and gives off heat energy effectively under a great
range of operating conditions.
Mixing 60% ethylene glycol with 40% water protects the cooling system from
freezing to -65 degrees Fahrenheit. Adding more anti-freeze does not prevent
freeze up at lower temperatures, but it does raise the boiling point of the
solution.
WARNING
Use care in handling anti-freeze. It is a petroleum based
liquid that can irritate the skin and eyes. The sweet
taste is appealing to animals and can be deadly if consumed. Check for local regulations on disposal and recycling.
Cooling System Thermostat and Radiator Pressure Cap
These two cooling system control devices affect heater system operation, including coolant temperature, circulation, boiling point, and coolant overflow
and recovery system. Figures 3-1 and 3-2 illustrate the function of the thermostat and radiator pressure cap respectively. Descriptions of how the thermostat
and radiator cap work follow the figures.
Go to Table of Contents - Index
3-1
,
,
,
,
,
,
,
,
Chapter 3 - Heater Components and Controls
COOLANT OUTLET
TO RADIATOR
CASTING
The thermostat is shown in
both closed and open positions. When closed coolant
does not circulate through
the radiator.
,,
,,
,
THERMOSTAT
PISTON
Figure 3-1
ENGINE BLOCK
COOLANT
FLOW
COOLANT
FLOW
THERMOSTAT VALVE CLOSED –
COOLANT CIRCULATES IN ENGINE
THERMOSTAT VALVE OPEN–
COOLANT CIRCULATES THROUGH
ENGINE AND RADIAOTR
,,
,,,
,,,,
,,,
,,,,,,
,,,
,,,
,,
,,, ,,
,,,,,,
,,,,
,,,,,,
,,,,
,,,,,,
,,,,
,,,
OVERFLOW PIPE
TO COOLANT
RESERVOIR
UPPER AND
LOWER SEALING
SEATS
Figure 3-2
The pressure radiator cap
seals the cooling system.
The cap pressure valve
opens when operating pressures are high.
CAP VACUUM
VALVE
CAP PRESSURE
VALVE
RADIATOR
UPPER TANK
RADIATOR
CORE
1. Thermostat - controls the direction of flow of the coolant
from the water pump, through the engine and radiator. As
the engine warms up the thermostat opens, allowing the
coolant to flow to the radiator. The coolant gives up excess
engine heat to the outside air as it moves through the radiator. If the engine is cold, the thermostat stays shut and the
coolant by-passes the radiator and circulates in the engine,
as well as the heater core.
2. Radiator – radiator cap seals the cooling system at the inlet
on top of the radiator. Caps are pressure rated to match
cooling system design. Each pound of pressure on the cooling
system raises the boiling point of coolant three degrees Fahrenheit, so the pressure cap extends the cooling system operating range above the normal boiling point. Coolant can flow
through the heater core regardless of thermostat position.
Altitude lowers the boiling point of coolant by two degrees Fahrenheit for every
1000 foot increase of elevation above sea level. As you can see, the pressure cap
tends to compensate for a lower boiling point at higher altitude. When high
system pressure forces the radiator cap to open, coolant escapes to the coolant
reservoir. A low pressure or slight vacuum inside the system sucks coolant back
to the radiator from the reservoir.
3-2
Go to Chapter Start - Table of Contents - Index
Water Pump
Water Pump
Modern water pumps have a centrifugal design. Vanes or impellers in the
pump circulate the coolant. Figure 3-3 shows a cutaway view of a water pump
assembly.
,,,,,,,
,,,,,
,
,,,,,
,,,,,
,,,,,
,,,,,,,,,,
FAN HUB
This cutaway drawing
shows the main components
of a water pump. Vane or
impeller type pumps work
best at high speed. Keep in
mind that the speed of the
pump is in proportion to
engine RPM.
BEARING AND
SHAFT ASSEMBLY
,,
,,
,, ,,,,,,
,,,,,,
,,
,,
,,
,,
Figure 3-3
SHAFT SEAL
ASSEMBLY
DRAIN
METAL OR
PLASTIC IMPELLER
WATER PUMP
BODY
Heater Components and Controls
The basic heater system components discussed in this section are:
1 . Heater Core
2 . Heater System Ducts
3 . Blower or Fan and Motor Assembly
4 . Hoses and Fittings
5 . Controls
1. Heater Core
Most heater cores are of tube and fin construction, with the inlet and
outlet on one end of the core. Hoses connect the core to the engine and are
held securely by hose clamps. Figure 3-4 illustrates a heater core. They
come in many sizes and shapes to meet cab space and heat energy
transfer requirements.
Figure 3-4
In the heater core heat
energy moves from the hot
engine coolant to the air in
the truck cab. Cores come in
all sizes and shapes to meet
heat transfer needs.
TUBE AND FIN
CONSTRUCTION
INLET AND OUTLET
ARE ATTACHED
TO MANIFOLD
ON THIS CORE
Go to Chapter Start - Table of Contents - Index
3-3
Chapter 3 - Heater Components and Controls
A large capacity heater core has more tubes and more fin area so that
more coolant can circulate through the tubes and more air moves through
the fins. The result is more heat energy transfer to the air in the cab.
2. Heater System Ducts
Ducts direct and control air as it circulates through the heating system.
The heater core housing is usually part of the duct system as is the blower
or fan assembly. Air outlet duct openings are usually located close to the
floor. The outlets are positioned to direct warm air to the feet and body of
the occupants.
All heater/defroster systems pick up some outside air and mix it with
cab air. They often have doors inside the duct system to regulate, mix or
restrict air flow as part of the heater control system. Many heater systems
use 100% outside air. Only auxiliary heaters use 100% cab air. Figure 3-5
illustrates typical heater system ducts with heater components. The
arrows indicate the air flow pattern through the duct system. This view of
a typical heater system does not include heater hoses, clamps, a water
valve or controls.
Figure 3-5
MOTOR & BLOWER ASSEMBLY
HEATER CORE
TO DEFROSTER
VENTS
HEAT–DEFROST
DOOR IN
DEFROST
(CABLE
CONTROLLED)
OUTSIDE AIR
TO FLOOR
VENTS
TEMPERATURE BLEND
AIR DOOR
(CABLE CONTROLLED)
The drawing illustrates the
relative position of the
heater core, a (pull through)
motor and blower assembly,
and two doors inside the
duct system. These doors
control air mixing at the
inlet side of the system and
direct the air to the cab and
defroster vents.
CAB AIR
3. Blower or Fan and Motor Assembly
Air movement in a heater system depends on the blower or fan. The
operator selects the motor speed to control the amount of air circulated
through the system. Motors have one to four speeds, depending on heater
design. Both single and double entry blower wheels are used. Figure 3-6
shows and describes typical motors, blower wheels, and a fan.
3-4
Go to Chapter Start - Table of Contents - Index
Heater Components and Controls
Figure 3-6
These illustrations show a
single shaft motor, double
shaft motor, double and
single entry blower wheels
and a four-bladed fan.
DOUBLE SHAFT
MOTOR
SINGLE SHAFT
MOTOR
SINGLE ENTRY
BLOWER WHEEL
FOUR BLADED FAN
DOUBLE ENTRY
BLOWER WHEEL
4. Hoses and Fittings
Heater hoses are usually 5/8", but may be 3/4" or 1" sizes. The heater inlet
hose may be smaller or the same size as the heater outlet hose. Hoses are
usually held in place by clamps. Some water valves shunt excess flow or
pressure back to the coolant return hose, assuring full flow of coolant and
relieving pressure on the valve.
5. Controls
The controls allow the operator to turn the heater on and off and regulate
the direction and quantity of warm air flow. Figure 3-7 shows a typical
heater control panel.
HEATER WATER
VALVE CONTROL
Figure 3-7
This heater control panel
includes water valve, defroster duct, and blower
motor controls.
BLOWER MOTOR
SWITCH
HOT
TEMPERATURE
COOL
OFF
DEF
CAB
AIR DIRECTION
FAN
DEFROSTER DUCT
DOOR CONTROL
When you turn the system on, the water valve opens to allow hot engine
coolant to flow through the heater core. The blower motor circulates cab
air through the heater core to warm the air. Water valves may be cable or
air operated. Figure 3-8 illustrates both types.
Go to Chapter Start - Table of Contents - Index
3-5
Chapter 3 - Heater Components and Controls
CABLE OPERATED WATER VALVE
AIR OPERATED WATER VALVE
AIR PRESSURE
Figure 3-8
This illustration shows air
and cable controlled water
valves.
FLOW
FLOW
CABLE CONTROL
When a separate control panel is installed in the bunk area of a cab, there
may be one type of control for the cab and another type for the sleeper. The
bunk control is often a thermostat, cycling the fan on and off to maintain
a constant temperature. Motor switches usually have one to three speed
positions plus off.
In a typical heater system, other controls you may encounter position
the doors inside the ducts to direct air flow. The defroster control is the
main one you will find in basic heater systems. This is usually a cable
controlled door that diverts warm air to the windshield or floor.
In HVAC systems the number of doors in the system and their function
will vary depending on system design. Doors operate electrically, manually, or automatically, by cable, vacuum, compressed air or by some
combination of these controls. In certain HVAC systems, the defrost mode
activates the air conditioning system. The air conditioner will dry the
heated air flowing to clear the windshield. This is commonly referred to as
a “defrost interlock.”
Chapter Review
• In review, the heat energy for heating cab air comes from the
hot engine coolant. The coolant is a combination of water and
anti-freeze (ethylene glycol). The engine water pump circulates coolant. The thermostat directs the flow of coolant in
the engine and to the radiator. The radiator pressure cap
allows the cooling system to operate under a preset amount of
pressure. Each pound of pressure increases the boiling point
of the coolant by three degrees Fahrenheit. The boiling point
drops by two degrees Fahrenheit for every 1000 feet of truck
operating elevation.
• Heater systems are designed to transfer heat energy from the
engine coolant to the air in the cab. A water valve controls
coolant flow to the heater core. A fan or blower forces cab air
through the fins of the heater core and heat from the coolant
is transferred to the air. The heater duct system and air
vents direct air movement in the cab.
3-6
Go to Chapter Start - Table of Contents - Index
Chapter Review
• There are various methods for controlling air temperature
and movement in a heater or HVAC system. In a simple
system there is usually an on-off switch for the fan or blower
motor. Most have three speeds plus “off.” The water valve
may be cable controlled, as is the defroster door. More complex systems may have air pressure switches and air controls, vacuum controls, electronic controls, and various doors
to control air flow direction.
• In heater systems air outlet temperature is controlled by one
of three methods:
1.
The water valve which varies the amount of coolant
passing through the heater core.
2.
A blend air door where cool air is mixed with heated air
to obtain the desired temperature.
3.
Electronic controls, which we will cover in Chapter 5 of
this manual.
• Full fresh air system designs use 100% fresh air in all but
“off ” and “maximum” air conditioning control settings. These
systems offer advantages you should be aware of. Fresh air
increases air pressure in the cab, thus any openings leak
outward. This eliminates cold spots and provides a more
uniform cab temperature. Air moving out of the cab openings
tends to act as a sound barrier and reduce cab noise levels.
The fresh air leaking out of the cab also provides a continuous change in the cab air and purges smoke, other air contaminants and any excess moisture.
• Some systems activate the air conditioner in the defrost mode
to remove moisture from the heated air. This ensures quick
defogging of the windows.
Go to Chapter Start - Table of Contents - Index
3-7
Chapter
4
Click on any of these
subject headings to go
directly to the page
Air Conditioner Components
• Refrigerant
• Lubricants
• Compressors
• Compressor Output
• Clutch
• Condensers
• Receiver-Drier
• Accumulator
• Expansion Valves & Other Metering Devices
• Evaporator Coil
• Blower/Fan & Motor Assembly
• AC System Ducts
• AC Hoses and Fittings
• Chapter Review
Refrigerant
The refrigerants we use in AC systems are commonly referred to as R-12 (Freon
12) or R-134a (HFC-134a). They have no color and only a slight odor. They are
non-toxic, non-corrosive and non-flammable chemicals in the form of liquefied
gas. Because the boiling point of a refrigerant is far below 0 degrees Fahrenheit, it is sold in sealed metal containers so it won’t evaporate.
WARNING
Although refrigerants are safe to use, they can be
dangerous to you and others if you do not use common
sense when you work with them. AC systems operate
under pressures much greater than the truck engine
cooling system. The containers refrigerants are sold
in are also under pressure. At 77 degrees Fahrenheit
outside temperature, the pressure inside the refrigerant container is 80 PSI. When released into the air, a
refrigerant boils away and becomes a gas. It’s temperature drops INSTANTLY. Please be sure to read
about safety and safe handling of refrigerants in
Chapter 6. Improper use can cause frostbite and eye
damage. Breathing refrigerant gas can result in respiratory problems, especially for people with cardiovascular disease.
Go to Table of Contents - Index
4-1
Chapter 4 – Air Conditioner Components
R-134a (HFC-134a) is gaining favor as the “environmentally friendly” substitute for R-12 in mobile HVAC systems. Properly designed R-134a systems will
equal or surpass the performance of R-12 systems, without danger to the
earth’s ozone layer. As the production of R-12 and other CFC chemicals ceases
during the mid-1990’s, more emphasis will be placed on the development of R134a systems and the recovery and recycling of R-12 in existing equipment.
Refrigerants have the ability to absorb and move a lot of heat energy from
inside a truck cab to the outside. This is because the refrigerant in the system is
controlled to change state at just the right temperature and pressure. Note in
Figure 4-1 that a refrigerant changes state in the condenser and the evaporator.
Figure 4-1
HOT HIGH
PRESSURE GAS
LOW PRESSURE GAS
[SUCTION SIDE]
In this drawing the AC
system is shaded to indicate
the high pressure side of the
system during AC operation. Controlled changes of
state occur inside the condenser and evaporator.
COLD LOW PRESSURE GAS
OUTSIDE AIR FLOW
EXPANSION
VALVE
COMPRESSOR
CAB AIR
FLOW
METERED
REFRIGERANT
CONDENSER
HIGH PRESSURE
LIQUID
EVAPORATOR
THERMOSTAT
RECEIVER-DRIER
Vehicle operating conditions such as engine RPM and air temperature influence actual AC system operating temperature and pressure. These factors,
along with the relative humidity, influence operator comfort (how efficiently
the system moves heat energy from the cab to outside air).
When a refrigerant changes from a high pressure liquid to a low pressure
gas in the evaporator, the refrigerant is much cooler than the air in the truck
cab. Nature's law takes effect, (remember how heat energy always moves from
a warm to a cooler environment) and the heat energy in the cab air moves into
the refrigerant in the evaporator coil. The refrigerant gets warmer and the cab
air colder. Figure 4-2 shows the refrigerant “change of state” in graphic form as
that change is related to pressure and temperature. The curved line indicates a
typical pressure/temperature range inside the evaporator and condenser.
When refrigerant enters the condenser (from the compressor) as a high
temperature high pressure gas, it is much hotter than the outside air. Again,
natures law takes effect and heat energy in the refrigerant moves into the air
as the air passes through the condenser fins.
4-2
Go to Chapter Start - Table of Contents - Index
Compressors
Figure 4-2
SYSTEM OPERATING PRESSURE (PSI)
This graph shows the pressure/temperature relationship of R-12 and R-134a
inside the AC system. Refrigerant is a liquid on the
left (shaded) side of the
curved line. On the right
side it is a vapor or gas.
TYPICAL HIGH
TEMPERATURE &
PRESSURE RANGE
IN CONDENSER
200
TYPICAL HIGH
TEMPERATURE &
PRESSURE RANGE
IN CONDENSER
200
175
175
150
150
125
125
100
100
LIQUID
LIQUID
75
75
VAPOR
50
50
TYPICAL LOW
TEMPERATURE &
PRESSURE RANGE
IN EVAPORATOR
25
0
-25°
VAPOR
0°
25°
50°
75°
100° 125° 150°
TYPICAL LOW
TEMPERATURE &
PRESSURE RANGE
IN EVAPORATOR
25
0
-25°
0°
25°
50°
75°
100° 125° 150°
SYSTEM OPERATING TEMPERATURES (°F)
R-12 REFRIGERANT
WARNING
R-134A REFRIGERANT
As controlled by federal law and in agreement with
other countries, the production of R-12 is being phased
out. Air conditioner systems with R-134a are appearing in many vehicles. These two refrigerants must not
be mixed. This means that different equipment must
be used in the handling of each refrigerant.
The Society of Automotive Engineers (SAE) has created certain Standards or Recommended Practices for
handling refrigerants. For example, different service
fittings are specified for R-12 and R-134a.
Combining R-12 and R-134a can result in poor cooling performance, higher operating pressures and inadequate lubricant circulation.
Lubricants
Lubricants, like other system components, are developed for use with specific
refrigerants. Mineral oil works very well with R-12 but becomes chemically
unstable with R-134a.
Polyalkylene glycols, called PAGs, are being considered by many for use with
R-134a. In addition, a family of ester based lubricants are being given serious
consideration.
The lubricant is in the system to protect the compressor from wear and
failure. With R-134a the compressor manufacturer specifies the lubricant best
suited to its product. On new R-134a systems labeling should identify the type
and amount of lubricant.
Go to Chapter Start - Table of Contents - Index
4-3
Chapter 4 – Air Conditioner Components
All PAG-based lubricants are not necessarily the same. Different compressor
manufacturers use different additives. Unlike the mineral oil lubricant for
R-12, you may need to keep several different lubricants on hand for use with
R-134a.
In retrofit systems use that lubricant recommended by the compressor
manufacturer.
Lubricants that come out of an air conditioning system should never be
reused. Contaminants and moisture are probably contained in such material.
Compressors
When a compressor is engaged and driven by the engine through the clutch
pulley, the compressor functions as a pump to move refrigerant and refrigeration
oil around the AC system. The compressor pistons move back and forth within
their cylinders as the compressor shaft revolves. A special lubricating oil is used
for each AC compressor. This oil, called refrigeration oil, is formulated to be
moisture free and compatible with the refrigerant used. It circulates throughout
the AC system. The lubricant used with R-12 is not compatible with R-134a.
We generally refer to an AC system as having a suction or low (pressure) side
and a discharge or high (pressure) side. The two sides of the system are divided
at the compressor, and at the expansion valve (refrigerant metering device)
located at the inlet to the evaporator.
The compressor pulls refrigerant gas from the evaporator, through the low
pressure suction hose, the inlet service valve and one way reed valves, and
into the compressor. During compression strokes, refrigerant gas is forced out
of the compressor through more one way reed valves, an outlet service valve
and a high pressure discharge hose to the condenser. The pressure from
compressor action moves the refrigerant through the condenser, receiver-drier
and connecting hoses to the expansion valve. Figure 4-3 shows typical compressor function in the AC system. Note the parts of the system under high
and low pressure.
,,
,,
,,
,,
,,
,,
INLET
OUTLET
PISTON ON
DOWNSTROKE
AND
UPSTROKE
DOWN
COMPRESSOR INLET IS SUCTION SIDE (LOW
PRESSURE) – COOL LOW PRESSURE GAS
SUCKED IN FROM EVAPORATOR
Figure 4-3
In these drawings of a twocylinder compressor the
suction or low pressure side
and discharge or high pressure side are noted in a
cutaway view.
UP
COMPRESSOR OUTLET IS DISCHARGE SIDE
(HIGH PRESSURE) – HOT HIGH PRESSURE GAS
FORCED OUT TO THE CONDENSER
We deliver power to the compressor through the clutch pulley. The pulley is
driven by a V-belt connected to another pulley powered by the truck engine.
The location of the compressor relates to the truck design and options, available space under the hood, and the AC system components selected.
4-4
Go to Chapter Start - Table of Contents - Index
Compressors
CAUTION
Heavy duty vehicles are subject to severe extended
use and much more vibration and road shock than
passenger cars. For this reason secure compressor
mounting, accurate pulley alignment and proper belt
tension are very important. The compressor mounting bracket is adjustable to allow for proper belt tension.
Pulley alignment and belt tension are critical for efficient compressor operation
and good belt life. To tension the V-belt properly, the compressor or it’s mounting bracket must be adjustable and securely bolted in position when attached
to the engine.
The proper type and amount of lubrication is critical to achieving good
compressor life.
The five types of compressors you are likely to encounter in your work are:
1. Two-Cylinder Compressor
2. Four-Cylinder Compressor
3. Five-Cylinder Compressor
4. Six-Cylinder Compressor
5. Wankel Compressor
Each is identified in the photos in Figure 4-4. They are different in design and
construction, but all do the same job.
Figure 4-4
The compressor designs
shown here all function to
move refrigerant and refrigeration oil around inside an
AC system. The two, four,
five, several six cylinder,
and the Wankel compressors are illustrated.
CCI OR TECUMSEH TWOCYLINDER
ZEXEL
HARRISON (GM) SIXCYLINDER AXIAL
SANDEN FIVE-CYLINDER
HARRISON (GM) FOUR
CYLINDER RADIAL
WANKEL RADIAL
Go to Chapter Start - Table of Contents - Index
HARRISON (GM) SIXCYLINDER DA-6 (METRIC)
4-5
Chapter 4 – Air Conditioner Components
1. Two-Cylinder Compressor
Many two-cylinder compressors are in use today. The Tecumseh has a cast
iron body and the York or CCI (Climate Control Inc.) is made of cast
aluminum. Both use reed valves mounted in a valve plate between the top
of the cylinders and the cylinder head. These in-line compressors may be
mounted horizontally, vertically or any angle in between. A pressure
differential of low pressure at the intake and high crankcase pressure—
along with centrifugal force from the rotating crankshaft—create lubrication pressure for oil circulation. The service fittings for charging or
evacuating the AC system are attached to the cylinder head of these
compressors.
2. Four-Cylinder Compressor
Four-cylinder radial compressors are produced by Tecumseh and
Harrison (GM). The cylinders are arranged inside a round housing in such
a way that they radiate from the center like the spokes of a wheel. The
pistons are moved in and out within the cylinders by a scotch yoke. A
scotch yoke is like a figure eight-shaped cam. The yoke pushes two
opposite pistons out to the top of their stroke and pulls the other two in to
the bottom of theirs. Each of the cylinders has it’s own reed valve plate.
The movement of the pistons circulates the refrigerant oil.
3. Five-Cylinder Compressor
The five-cylinder axial compressors made by Sanden and Zexel have five
cylinder bores, each fitted with a piston. The pistons are moved back and
forth by a rod that is attached to a rotating cam rotor by a ball and socket
joint. A reed valve plate mounts between the top of the cylinders and the
cylinder head. An inlet and a discharge port are mounted on the cylinder
head. The pressure differential between the inlet pressure and the pressure inside the crankcase forces lubricating oil to all of the moving parts
in the system.
Note:
Seven cylinder compressors will be found on many
R-134a applications.
4. Six-Cylinder Compressor
Six-cylinder axial compressors are made and marketed by Zexel, GM
(Harrison Division), Ford, Chrysler and Nippondenso. All have three
cylinder bores, each fitted with double-acting pistons. The pistons have a
head on both ends. As they move back and forth inside the cylinder bores,
they cause each bore to act as two separate cylinders. The pistons are
moved by a swash plate that is mounted on the compressor shaft. These
compressors have two reed valve plates, one at the front and one at the
rear. Internal passages join the six cylinders so that refrigerant can flow
into and out of all cylinders through the one high and one low side service
fitting mounted on the rear of the compressor.
4-6
Go to Chapter Start - Table of Contents - Index
Compressor Output (Efficiency)
The Zexel compressor has design improvements for easy seal replacement. The General Motors (Harrison) DA-6 is a downsized, lightweight
version of earlier GM A-6 six cylinder axial compressors. The DA-6 is easy
to service or repair, and has all metric dimensions. It looks different than
the old A-6 but works the same way internally. Components have smaller
dimensions so parts are not interchangeable with the A-6.
5. Wankel Compressor
The Wankel Rotary compressor, has a figure eight-shaped cavity in the
compressor center housing. A triangular rotor is driven by gears from the
compressor drive shaft. As the rotor turns, a low pressure (suction) is
formed at the suction ports and a high pressure is built up at the discharge ports. The suction and discharge ports are located on the compressor end plate, along with the two service ports. There is no suction valve,
only a discharge valve.
Compressor Output (Efficiency)
Engine speed has an effect on the output of all compressors. The two charts in
Figure 4-5 show typical compressor output variations. The column of numbers
on the left of each chart represent BTU’s per hour (x1000) based on the
compressor speeds (RPM) shown across the bottom. As you can see, the faster
the engine turns the compressor shaft, the greater the output. Note how
rapidly output is increased by operating speed of the compressor, and the effect
suction pressure (operating conditions) can have on compressor output. Actual
operating conditions will affect these performance curves.
Note:
Larger capacity compressors like the Climate Control
Inc. 210 and Sanden model 510, are frequently specified for heavy duty vehicle applications. Larger capacity compressors are very important when a separate bunk AC unit is part of the system.
Go to Chapter Start - Table of Contents - Index
4-7
Chapter 4 – Air Conditioner Components
YORK MODEL 210
COMPRESSOR OUTPUT
ZEXEL
COMPRESSOR OUTPUT
PSIG
SUCTION
40
45000
Figure 4-5
PSIG
SUCTION
45000
40000
40000
40
35000
20
30000
25000
20000
15000
180 PSIG DISCHARGE
65° F RETURN
15° F SUBCOOLING
10000
5000
REFRIGERANT CAPACITY IN BUT'S PER HOUR—R-12
REFRIGERANT CAPACITY IN BUT'S PER HOUR—R-12
30
35000
Each chart plots compressor
output curves at three
suction pressures or PSIG
(pounds per square inch
gauge). The three pressures
represent variations in
operating conditions for
these two compressors.
30
30000
20
25000
20000
15000
180 PSIG DISCHARGE
65° F RETURN
15° F SUBCOOLING
10000
5000
0
0
0
1000
2000
3000
COMPRESSOR SPEED IN RPM
4000
0
1000
2000
3000
4000
COMPRESSOR SPEED IN RPM
Clutch
The clutch is driven by the truck engine through a V-belt running in a grooved
clutch pulley. The clutch pulley rides on ball bearings and can turn without
driving the compressor shaft. Heavy duty clutches have double row ball bearings. An electromagnetic coil is mounted inside the pulley housing and bolted to
the compressor body. The clutch drive plate is bolted to the compressor shaft.
There is a small amount of clearance between the plate, pulley and coil.
When the AC system thermostat control in the evaporator calls for cooling,
current flows through the coil inside the pulley. This sets up a magnetic field
between the drive plate and the pulley. The magnetic field locks the pulley to
the drive plate, causing the pulley to turn the compressor shaft. When the
clutch is not engaged the pulley spins free without turning the compressor.
Electrical connection to the clutch coil is made through lead and ground
wires. Figure 4-6 illustrates the clutch mounted on a compressor.
4-8
Go to Chapter Start - Table of Contents - Index
Condensers
Figure 4-6
A clutch is shown in this
illustration. Typically, a
thermostat in the evaporator acts as a switch and
directs electrical current to
the clutch coil. When the
coil is energized the drive
pulley turns the compressor
shaft.
CLUTCH COIL LEAD
WIRE TO EVAPORATOR
THERMOSTATIC
SWITCH
CLUTCH
COMPRESSOR
Note:
In some systems (primarily GM systems) the clutch
remains engaged to drive the compressor continuously
during normal operation of the air conditioner. System
pressure and refrigerant flow are controlled using suction throttling or POA valves at the outlet of the evaporator.
Condensers
Condensers transfer heat energy to the outside air. Condensers may be
mounted on the roof, or behind the grill on the front of the radiator, or may
replace the grill. There are many shapes and sizes to accommodate AC system
design requirements. They include:
1. Radiator Mounted
a. Serpentine
b. Parallel Flow
c. Tube & Fin
2. Remote Mounted
Radiator-mounted condenser construction, currently in use, is as follows:
a. Tube and fin construction is characterized by the use of round
tubes inserted through fin material and then expanded. Hairpin
tubes are used to complete the circuit. This is the strongest type of
construction.
b. Serpentine construction uses single, flat tubing containing multiple passages that snake from the top to the bottom of the core.
Fins are either the Skyve-type or brazed-ribbon. Serpentine condensers are 3/4 to 2 inches thick and exhibit high heat rejection in
a compact size. The pressure drop through the core is most often
greater when compared to tube and fin construction.
c. Parallel-flow condensers are highly efficient, using brazed-ribbon
fins. This is the most efficient type of construction, but is not as
strong as either tube and fin or serpentine. There is also a greater
pressure drop through the core than the tube and fin style.
Go to Chapter Start - Table of Contents - Index
4-9
Chapter 4 – Air Conditioner Components
Refrigerant flows through the condenser tubing from top to bottom. The fittings are located for convenience of assembly. As hot refrigerant gas from the
compressor moves through the condenser tubing, it gives up heat energy to the
outside air stream. The refrigerant gas becomes cooler and at the right temperature and pressure will “change state” in the condenser and become a
liquid. This change usually takes place in the bottom third of the condenser.
Condenser function requires the movement of a large amount of air between
the condenser fins. The air passing through the fins absorbs BTU’s of heat
energy from the hot, high pressure refrigerant gas inside the condenser. Engine
radiator or auxiliary fans must work properly and the condenser fins must be
kept clear of debris or obstructions for efficient condenser function. Figure 4-7
shows several types of condensers.
RED DOT GRILLDENSER
(CONDENSER REPLACES
GRILL)
Note:
TUBE AND FIND CONDENSER
(REMOTE MOUNT TYPE)
SERPENTINE CONDENSER
(RADIATOR MOUNT)
Figure 4-7
These condenser types are
explained in the illustrations. The typical behind
the grill condenser, a remote mounted unit and a
Grilldenser.
When refrigerant gas gives up heat to the outside air
and becomes a liquid inside the condenser—it is still
hot. Review the graph (Figure 4-2) for a moment and
note how hot the condenser temperature can be when
the refrigerant gas changes to a liquid inside the
condenser.
Most condensers are mounted in front of the radiator and attached to radiator
supports or the hood assembly. This location is the least costly for several
reasons: the engine cooling fan eliminates the need for a separate condenser
motor/fan assembly; the refrigerant hose to and from the condenser can be
shorter; and the condenser is better protected from the weather.
A Grilldenser is a condenser design that takes the place of a decorative nonfunctional grill in front of the radiator.
Remote mounted condensers (such as roof mounts) are normally used when
there is no room for front mounting. Other reasons for remote mounted condensers are:
•
•
•
•
4-10
A lack of room between the radiator and grill
Critical engine cooling requirements
Use of a radiator mounted air-to-air intercooler
Insufficient airflow on off-highway equipment, pick-up or delivery
vehicles
Go to Chapter Start - Table of Contents - Index
Accumulator
Note:
Intercoolers, are also called aftercoolers or chassismounted charge-air coolers. These devices may be
installed on the engine or in front of the radiator on
some heavy duty vehicles. They are designed to
achieve improved fuel economy and performance, and
lower emissions by reducing air temperature at the
intake manifold. The cooler, denser air boosts horsepower, efficiency and engine durability. For these
reasons, intercooler installation is on the increase on
heavy duty trucks.
In some intercooler applications, the condenser used for AC may be mounted in
front of the radiator and below the intercooler. Figure 11-9 in Chapter 11 shows
this condenser location.
Receiver–Drier
The receiver-drier functions as a drier, refrigerant filter and temporary storage
tank for refrigerant moving through the AC system. When refrigerant leaves
the condenser as a liquid, it flows to the receiver-drier. Figure 4-8 shows a
cutaway view of a receiver-drier. Refrigerant enters at the top and flows
through a desiccant material and filter before it moves on through a pickup
tube near the tank bottom. The most common desiccant is a molecular sieve.
This is a porous material, usually in the form of 1/8 inch balls, that attract and
hold moisture.
The desiccant commonly used with R-12 is identified as XH-5. It is not
compatible with R-134a. Many driers in both new and replacement systems are
now using an XH-9 desiccant which is compatible with both R-12 and R-134a.
Driers that do not carry a special labeling are probably only good for R-12
usage.
Figure 4-8
This illustration shows the
inside of a typical receiverdrier. Note the path of the
arrows which indicate the
movement of refrigerant.
The desiccant, filter(s), and
screens trap any water or
particles that might accidentally be inside the system.
SIGHT GLASS MAY INCLUDE
MOISTURE INDICATOR
OUTLET TO EXPANSION VALVE
INLET FROM CONDENSER
SPRING
MOISTURE AND CONTAMINANTS
TRAPPED BY FILTERS, SCREENS,
AND DESICCANT
FILTER PADS
AND SCREENS
PICKUP TUBE
RECEIVER-DRIER
Note:
Moisture (water) or particles can cause system malfunctions and corrosion. They can block the natural
flow of refrigerant at the expansion valve. Moisture
can change state there and form ice. It may also mix
with the other elements inside the system ( refrigerant and the oil) to form acid.
Go to Chapter Start - Table of Contents - Index
4-11
Chapter 4 – Air Conditioner Components
Sometimes refrigerant that leaves the condenser is part liquid and part vapor.
When this happens the receiver-drier acts as a separator. The liquid refrigerant settles to the bottom of the tank where the pickup tube inlet is located.
Receiver-driers vary in size and shape and many have a sight glass to aid in
system diagnosis and charging. A sight glass may include a moisture indicator
to let you know if the system is contaminated with moisture. There are high
capacity units, variations in mounting location, fitting types, and the number
and position of filter elements for receiver-driers.
The preferred receiver-drier design for heavy duty vehicle applications is
shown in Figure 4-8. Sandwiched between the two metal baffles are a screen,
two fiberglass filter pads, and at least ten cubic inches of desiccant. In this
design the desiccant is squeezed between the two filter pads. This helps
prevent movement of the molecular sieve material as the refrigerant flows
through. As a result, there is less chance of desiccant breakdown and loose
material reaching and blocking the expansion valve.
AC system design may include single or multi function pressure switches, a
pressure relief valve or fuse plug. These are usually mounted on or connected to
the receiver-drier.
Accumulator
Some AC systems use an accumulator for temporary refrigerant storage instead of the usual receiver-drier. An accumulator is located close to the evaporator outlet and stores excess refrigerant before it moves on to the compressor.
When an accumulator is used instead of a receiver-drier, the typical expansion
valve is replaced with an expansion tube (also called a fixed orifice tube).
An expansion tube allows refrigerant to flow continuously through the
evaporator. At times the refrigerant does not all change to gas and may enter
the accumulator as a liquid. The accumulator prevents liquid refrigerant from
going to the compressor. The pickup tube opening inside an accumulator is at
the top as shown in Figure 4-9.
CAUTION
4-12
Serious damage results when liquid is sucked into the
compressor.
Go to Chapter Start - Table of Contents - Index
Evaporator Coil
Figure 4-9
OUTLET
The accumulator has filtering elements like a receiverdrier. Parts are named in
this drawing and arrows
show the path refrigerant
follows as it moves through
the accumulator.
INLET
CONNECTOR FOR PRESSURE
SWITCH IF USED
PICKUP TUBE
DESICCANT BAG
LIQUID BLEED HOLE
FILTER SCREEN
Most AC systems with an accumulator have a thermostat to control the clutch.
The thermostat is usually positioned to sense refrigerant temperature between
the evaporator outlet and the accumulator. Some AC systems with an accumulator have a pressure switch mounted on the accumulator to control the
compressor clutch.
Expansion Valves & Other Metering Devices
Various types and designs of refrigerant metering or control valves are used in
AC systems. The valves are actuated by temperature and/or pressure. All are
designed to control the flow of refrigerant into and/or out of the evaporator or
compressor.
In addition to the block type expansion valve shown and described in
Chapter 2, Figure 2-7, there are other valve designs. The types of expansion
valves discussed in this section are:
1. Thermostatic Expansion Valves
2. Expansion Tubes
1. Thermostatic Expansion Valves
The traditional internally and externally equalized expansion valves each
work the same way. Valve function is controlled by temperature and
pressure of the refrigerant gas as it leaves the evaporator on it’s way back
to the compressor. A small diameter hollow tube (capillary tube) is attached to the top of the valve diaphragm housing.
The capillary tube contains a small amount of gas or liquid such as
refrigerant. The coil or bulb at the end of the tube is clamped to the outlet
manifold from the evaporator. The gas in the capillary tube expands and
contracts from heat in the outlet tube. It pushes to open the valve orifice.
Go to Chapter Start - Table of Contents - Index
4-13
Chapter 4 – Air Conditioner Components
The valve opens and closes depending on system need for refrigerant at
the inlet to the evaporator. Figure 4-10 shows an internally equalized
valve.
Figure 4-10
PRESSURE
FROM
CAPILLARY
PRESSURE
The internally equalized
TXV is shown. This valve is
designed with either temperature sensing coils or
bulbs at the end of its capillary tubes.
OUTLET
INTERNALLY EQUALIZED VALVE
Note:
Insulating material is wrapped around the expansion
valve, and coil or bulb where it attaches to the evaporator outlet. This is done to improve heat energy
conduction and prevent condensation forming on the
valve.
2. Expansion Tubes
Expansion tubes are also called fixed orifice tubes. They are used in some
systems, always in combination with an accumulator instead of a receiver-drier. The tubes have no moving parts and are not adjustable.
When used, an expansion tube is located inside the inlet tube of the
evaporator. It restricts but allows a continuous flow of refrigerant to the
evaporator coil.
An expansion tube is shown in Figure 4-11. When an expansion tube is
used in place of a valve, liquid refrigerant may pass through the evaporator before it can change to a gas. The accumulator prevents liquid refrigerant from reaching the compressor. When an expansion tube is defective it
must be replaced using a special tool.
Figure 4-11
EXPANSION TUBES FIT INSIDE
THE EVAPORATOR INLET FITTING
The expansion (fixed orifice)
tube is used in place of an
expansion valve. There are
no moving parts.
O-RING
ORIFICE TUBE
4-14
Go to Chapter Start - Table of Contents - Index
Evaporator Coil
Evaporator Coil
Evaporator coils come in various shapes and sizes. Most are of fin and tube
construction. The fins and tubing are designed to transfer heat from the cab air
to the cool refrigerant vapor as it moves through the evaporator tubing. The
fins are colder than the cab air, so moisture in the air blown across the coil
condenses on the fins. The moisture forms into droplets and drains to the
bottom of the evaporator housing and out of the cab through a drain tube. Dust
or other airborne particles may also be trapped in the condensed moisture
droplets. In this way the AC system dehumidifies, filters and cools the air in the
cab.
Refrigerant enters the evaporator coil, expands rapidly and changes state
(drops in temperature and pressure). The refrigerant absorbs heat energy from
the air in the cab and moves through the tubing to exit the evaporator coil. A
variety of expansion valve or other refrigerant flow regulating devices (described earlier) are used in an AC system design, at the inlet to and/or the
outlet from the evaporator coil. Each is designed to control the flow of refrigerant to provide maximum heat transfer in the evaporator. The drawing, Figure
4-12, is a cutaway view of a typical evaporator coil.
COLD LOW PRESSURE GAS
Figure 4-12
The evaporator coil illustrated is mounted inside an
enclosure (not shown) designed for efficient air flow
between the fins of the
evaporator.
CAB AIR
FLOW
EXPANSION VALVE
METERED REFRIGERANT
THERMOSTAT
EVAPORATOR
Air Conditioner Blower/Fan and Motor Assembly
In HVAC system designs, a blower assembly is positioned to move air through
the evaporator coil and heater core. For efficient air movement, the air must be
confined within a housing. The blower assembly used in a system may be
located for functional or space considerations. Some pull air and others push
air through evaporator and/or heater fins.
Fans are used to move air through the fins of the condenser. In underhood
applications the engine cooling fan is used. Roof or remote mounted condensers
have separate fan/motor assemblies.
Go to Chapter Start - Table of Contents - Index
4-15
Chapter 4 – Air Conditioner Components
Figure 4-13 shows both evaporator blower and condenser fan assemblies in a
roof mounted air conditioner. An outer cover directs the flow of outside air
through the condenser. The fan blows the air out through an opening in the top
of the cover. The blower assembly pulls air from the cab, through the evaporator coil and back into the cab. An inner cover encloses the evaporator and
blower assembly to control cab air flow.
OUTER COVER PROTECTS SYSTEM
AND DIRECTS RAM AIR THROUGH CONDENSER
Figure 4-13
INNER COVER ENCLOSES
EVAPORATOR AND
BLOWER ASSEMBLY
In this roof top air conditioning system the fan and
blower assemblies pull air
through the condenser and
evaporator.
Air Conditioner System Ducts
In Figure 4-13 above, outer and inner component covers are shown. When
fastened in position, they control air flow direction. AC system ducts come in
different shapes and sizes to fit space requirements. The positions of doors and
louvers control air movement and flow in the cab. Figure 4-14 shows a
combination HVAC blend air duct system. The doors in a duct system could be
controlled by cable, vacuum, compressed air, electric, or by a combination of
these controls. Some function automatically, while others are controlled by the
operator.
4-16
Go to Chapter Start - Table of Contents - Index
Chapter Review
Figure 4-14
HEATER WATER VALVE
This HVAC system cutaway
drawing shows the various
duct doors and the air flow
pattern. Most heavy duty
HVAC systems have a
stacked core arrangement
where air passes through
both coils.
DEFROSTER
DOOR
DEFROSTER
OUTLET
HEATER CORE
EVAPORATOR CORE
AC
OUTLET
CAB AIR INLET
BLOWER
MODE
DOOR
HEATER
OUTLET
OUTSIDE
AIR INLET
Figure 4-15
This is a cutaway of a standard stacked core arrangement.
BLOWER
HEATER CORE
AIR FLOW
EVAPORATOR CORE
Air Conditioner Hoses and Fittings
The refrigerant hoses used in air conditioning systems are much stronger than
heater or radiator hoses because of pressure restraints. These are available in
single braid, double braid and nylon lined rubber hoses.
Fittings of many types, shapes and sizes may be used depending on the
application and location. There are push on, flare, O-ring and quick disconnect
fittings. Various adapter, step up, tee block, splicer and special application
fittings may be used as connectors during initial installation, service or when a
system is modified.
Chapter Review
• The standard refrigerants used in vehicle air conditioning systems are R-12 and R-134a. Although safe to use, a refrigerant
may be dangerous if not handled carefully. At sea level
pressure, a refrigerant will boil at a very low temperature.
A refrigerant can be controlled to change it’s state inside the AC
system and absorb, move and give up a large amount of heat
energy. A refrigerant is cold in the evaporator and hot in the
condenser.
Go to Chapter Start - Table of Contents - Index
4-17
Chapter 4 – Air Conditioner Components
• All compressor designs function as pumps to move or circulate
refrigerant inside the AC system. Compressors are driven
through a clutch pulley and V-belt by the engine. For efficient
operation, a compressor must be mounted securely with proper
belt tension and alignment. Engine speed and suction pressure
have an effect on compressor output. Higher engine RPM means
greater output.
• The clutch is used to drive the compressor. In most AC systems a
thermostat cycles the clutch on and off, although in some designs
the clutch stays on during AC operation.
• Condenser construction allows heat energy transfer to the outside
air. Refrigerant changes state in the condenser, from a high pressure and temperature gas to a liquid. It is important to keep the
condenser free of dirt and debris for good air flow through the fins
and efficient heat transfer. The various condenser designs all
function the same way.
• Receiver-driers function as a refrigerant drier, filter and temporary storage tank. The filter and desiccant material trap and hold
moisture or other contaminants that may be inside the AC system. The receiver-drier traps any vapor leaving the condenser.
Some designs incorporate a sight glass, moisture indicator and/or
various other control devices.
• An accumulator may be used in place of the receiver-drier as a
temporary storage tank for refrigerant. This device controls the
flow of refrigerant to the compressor and also traps contaminants
and moisture. Accumulators are used with AC system designs
that have an expansion tube. They prevent liquid refrigerant from
flowing to the compressor.
• There are a variety of thermostatic expansion valves (TXV’s) and
other refrigerant flow regulating devices in use today. All control
the flow of refrigerant in the AC system to manage the movement
of heat energy. There is the block expansion valve, traditional
expansion valve, and expansion tube. Some AC system refrigerant flow regulating assemblies combine several components to
control refrigerant flow.
• The construction of an evaporator coil is designed to transfer heat
energy from the cab air to the refrigerant inside the tube. The
evaporator coil also helps to clean and dehumidify the air in the
cab. Moisture in the air condenses on the fins of the evaporator
coil, then drips off the fins and drains out of the cab. When
refrigerant enters the evaporator there is a quick drop in pressure. The refrigerant expands rapidly, changes state and drops in
temperature.
• Blower, fan and motor assemblies increase the movement of air
for efficient cooling (heat energy transfer). The duct system controls the air flow direction.
• The hoses and fittings used in AC systems connect the various
components together. They enclose or contain the refrigerant as it
moves around inside the system.
4-18
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Chapter Review
• There is a high and low pressure side in an AC system. The high
side begins inside the compressor. High pressure continues
through all fittings and hoses that connect the condenser, the
receiver-drier, and expansion valve or other refrigerant metering
device at the inlet to the evaporator. As refrigerant leaves the
expansion valve or other metering device and enters the evaporator tubing, the pressure drops. It remains low in hoses and any
components that connect or control the refrigerant as it moves
into the suction side of the compressor. AC system components
allow refrigerant to change state easily. They control and contain
refrigerant as it moves inside the system.
Go to Chapter Start - Table of Contents - Index
4-19
Chapter
5
Click on any of these
subject headings to go
directly to the page
System Controls
• Air Conditioner Controls
• Heater Controls
• HVAC Control Variations
• Chapter Review
Air Conditioner Controls
The following air conditioner controls are discussed in this section:
1. Active Controls
2. Passive Controls
3. Compressor Clutch Controls
4. Refrigerant Flow Controls
5. Sleeper Unit Controls
System controls accomplish three things. They maintain cab temperature
(control the air in the cab, refrigerant and engine coolant), protect system
components and related parts from damage or excessive wear, and allow design
and operating condition flexibility. This chapter explains control devices in
more detail.
Active Controls are used by the driver or a passenger to turn the system
on, and adjust air temperature, air flow direction and velocity. The controls are
switches, levers, and air louvers or diffusers.
Passive (Automatic) Controls regulate the flow of refrigerant or coolant.
These include thermostats and various pressure activated or regulating valves,
pressure and temperature switches. Some controls shut down or prevent system operation under certain conditions.
Control Devices are used to open, close, adjust, engage or disengage parts
of the system. Examples are air cylinders, air switches, solenoids and other
electronic controls. Some system designs take advantage of air pressure and
electronics, for more precise control of components and reduced maintenance.
Combination and supplemental control devices can affect system operation. They may prevent, interrupt or support system functions. Examples
are ambient temperature switches, Binary™ or Trinary™ (multi-function)
switches, radiator fan clutches and radiator shutter systems.
Note:
Keep in mind that air conditioning and heater systems are closed (sealed) and function under pressure.
Control devices take advantage of system pressure
and heat energy. A few control devices are influenced
by conditions outside the system.
Go to Table of Contents - Index
5-1
Chapter 5 – System Controls
1. Active Controls
Active control types depend on system design, location and available
space. When a heater or AC system has been installed as a separate or
supplemental unit (perhaps in the sleeper cab), there is probably more
than one control panel location.
The integrated HVAC control panel shown and described as Figure 5-1
is mounted in the dash. With these controls, the AC and heater systems
may be turned on, the temperature adjusted, air directed and mixed, and
air velocity controlled.
AIR DIRECTION LEVER
CONTROLS CAB AIR FLOW
FAN SWITCH
FOR 3 SPEED
BLOWER
CONTROL
Figure 5-1
HVAC in-cab controls are
described in this illustration.
HIGH
RECIRC
FRESH
VENT
FLOOR
A/C
MED
BILEVEL
HEAT
DEF
LOW
TEMPERATURE
OFF
COOL
HOT
TEMPERATURE CONTROL LEVER
FOR MODULATING WATER VALVE
When the air direction lever is in the AC mode, power is directed to the
thermostat and from there to the compressor clutch. As the AC unit
operates, the thermostat cycles the clutch on and off automatically. Some
controls have a separate heat-AC switch for this purpose.
The slide controls could be connected to push-pull cables or an electric
or air control module. With air or electric controls and the lever in the
RECIRC mode, air within the cab is recirculated through the evaporator.
In all other positions, fresh air is brought in from outside the cab. Some
control panels have a separate fresh/recirculating air switch or lever.
The fan control knob is connected to a four position switch. There are
three “on” positions to control blower speed and regulate air velocity
(CFM) in the system.
Note:
Blower or fan speed affects air temperature. At lower
speeds the cab air moves more slowly through the fins
of the evaporator or heater, so more heat energy
moves into or out of the cab air than at faster air
speeds (CFM). Thus air leaving the vents or louvers
will be colder or warmer.
Most air vents or louvers in the cab may be adjusted by hand to moderate
and direct air movement. These are in various sizes, shapes and locations
in the cab.
The thermostat and expansion valve or refrigerant metering device
basic controls because they are necessary in any system. Both function
automatically after the system is turned on.
5-2
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Air Conditioner Controls
2. Passive Air Conditioner Controls
Most automatic controls function in response to AC system temperature
(degrees Fahrenheit) or pressure (PSI) conditions. The thermostat is a
good example. It uses temperature to automatically cycle the compressor
clutch.
3. Compressor Clutch Control
The different types of compressor clutch control are described below.
Thermostatic Control
A thermostat in a basic air conditioning system controls the electrical circuit to the clutch. Most thermostats have a capillary tube that
is inserted between the fins of the evaporator coil. The depth of tube
insertion and location in the coil are critical to system performance.
Thermostats are either fixed set or adjustable. A fixed set control
will operate in the 32 degrees to 38 degrees Fahrenheit range. An
adjustable thermostat functions between 32 degrees and 50 degrees
Fahrenheit and may be controlled with a knob or push-pull cable.
Figure 5-2 shows these types of thermostats.
Figure 5-2
Two thermostats are shown.
They are used to cycle the
compressor clutch on and off
at selected high and low
temperatures.
FIXED SETTING THERMOSTAT,
PRESET TEMPERATURE
CABLE CONTROLLED THERMOSTAT VARIABLE TEMPERATURE
The thermostats shown have sealed capillary tubes that sense temperature. The capillary tubes contain a small amount of heat sensitive gas or liquid like R-12. System temperature variations raise and
lower pressure in the sealed capillary tube. This pressure activates a
switch inside the thermostat to open and close the electrical circuit
to the clutch. These thermostats may sense temperature in the
evaporator coil or at the evaporator outlet.
Another type of user adjustable rotary thermostat has a bimetal
heat sensing strip and has been used to control the temperature in
sleeper cab AC or HVAC systems. The bimetal strip senses air
temperature. When the sleeper box air is too warm (in AC mode), the
bimetal thermostat electrical circuit activates a blower motor and
opens a solenoid valve. The valve allows refrigerant to flow to a
separate evaporator used to cool air circulating in the sleeper compartment. This type of system design is illustrated in Chapter 11
(Figure 11-7).
Go to Chapter Start - Table of Contents - Index
5-3
Chapter 5 – System Controls
Pressure Switch Control
Most of the AC systems that have an expansion tube and accumulator (instead of an expansion valve and receiver-drier) use a thermostat to control clutch operation. However, there are some accumulator systems with a pressure sensing switch instead of a thermostat.
The switch opens and closes an electrical circuit to the clutch. Figure
5-3 shows this type of automatic compressor clutch control.
HIGH PRESSURE
VAPOR
Figure 5-3
CONDENSER
HIGH PRESSURE LIQUID
The accumulator system
schematic uses a pressure
sensitive electrical switch to
control the compressor
clutch. The switch senses
refrigerant pressure (PSI)
inside the accumulator.
COMPRESSOR CLUTCH
LOW PRESSURE
VAPOR
CIRCUIT TO CLUTCH
ACCUMULATOR
WITH PRESSURE SWITCH
ORIFICE
(EXPANSION)
TUBE
EVAPORATOR
LOW PRESSURE
LIQUID
When pressure (PSI) in the accumulator is high, the pressure sensing switch closes an electrical circuit and the clutch is engaged. If the
pressure is low, the switch opens the circuit to disengage the clutch.
4. Refrigerant Flow Control
In Chapter 4 we described devices frequently used to control refrigerant
flow into and out of the evaporator. Most are controlled by pressure,
temperature or a combination of both inside the system. Some AC systems
have two evaporators, one for the cab and the other for the sleeper
compartment. A freon solenoid valve may be used to split and direct part
of the refrigerant flow to a second evaporator. The solenoid valve is
electrically controlled and opens when the sleeper cab AC control is
operated. Figure 5-4 illustrates various refrigerant flow control devices
and explains what causes them to function.
5-4
Go to Chapter Start - Table of Contents - Index
Air Conditioner Controls
Figure 5-4
This group of illustrations
notes how the most frequently used refrigerant
metering or flow control
devices function.
EXPANSION TUBE HAS
NO MOVING ELEMENT
TYPICAL PRESSURE CONTROLLED
TXV (EXTERNALLY EQUALIZED)
,,
,,
,,
,, ,,
,,,
,,,
,,,
PRESSURE CONTROLLED
BLOCK TYPE TXV
ELECTRICALLY CONTROLLED FREON SOLENOID
VALVE
These controls are designed to meter refrigerant flow through the evaporator coil. Thermostat and compressor clutch function are independent of
these refrigerant flow control devices.
Note:
A thermostat or pressure switch controls the compressor clutch assembly. Automatic refrigerant metering devices sense pressure/temperature in the system and control refrigerant flow through the evaporator. The combination of controls keeps the system
balanced so that heat energy can move efficiently by
taking advantage of natures laws. When the system is
out of balance, refrigerant may move too fast or too
slowly. It will not absorb enough heat to cool the cab
properly, or may result in too low a temperature in
the evaporator. In some cases, the normal condensation collecting on the evaporator fins may freeze instead of draining out of the cab. The frozen condensate will block air flow through the evaporator. No air
flow—no cooling.
Many truck and off-road vehicles have control variations, combinations
and supplemental controls. We will explain these controls after we describe basic and automatic heater controls.
Go to Chapter Start - Table of Contents - Index
5-5
Chapter 5 – System Controls
5. Sleeper Unit Controls
The most familiar type of temperature control is the bi-metallic thermostat. In this type of control, two strips of dissimilar metals are bonded
together, such that as the temperature changes, the two metals expand or
contract at different rates. These changes cause the strips to bend, making contact and completing or breaking a circuit to control the bunk HVAC
unit. The bi-metallic control needs good airflow through the control panel
in order to react.
The electronic controls for sleeper units have a sensor (or thermistor)
which will detect temperature changes. This sensor is very small and can
be unobtrusively mounted on the front of the control panel. This type of
control has a far narrower “dead band,” the temperature change needed
for the control to react. This allows the sleeper box temperature to be
more closely controlled than with a bi-metallic thermostat. The small size
of the sensor mounted on the front of the control panel allows the panel to
be mounted flush with the walls of the sleeper box.
Heater Controls
The following heater controls are discussed in this section:
1. Active Heater Controls
2. Vacuum Controls
3. Passive Heater Controls
1. Active Heater Controls
Let’s look at a typical heater control panel. There are a couple of slide bars
connected to cables or air lines. The blower (or fan) motor control knob is
attached to a four position switch. Figure 5-5 shows the panel connected
to system components. System design and component locations will vary
from one vehicle to another.
5-6
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Heater Controls
Figure 5-5
SLIDE CONTROL
LEVERS
Typical heater system controls and locations are
shown and described in this
drawing.
HEATER SYSTEM CONTROL PANEL
HOT
TEMPERATURE
COOL
OFF
DEF
CAB
FAN
AIR DIRECTION
CABLE TO
WATER VALVE
CABLE TO
DUCT DOOR
(HEAT/DEFROST)
CIRCUIT TO BLOWER
DEFROSTER DUCT
COOLANT LINE
TO HEATER (PRESSURE)
HEATER CORE
BLOWER AND
MOTOR
COOLANT
LINE RETURN
(LOW PRESSURE)
COOLANT (WATER)
VALVE
FAN CLUTCH
WATER PUMP
A water valve is the primary control for a basic heater system. When the
valve is open, hot engine coolant flows through the heater core and back to
the engine. The driver can adjust the control to modulate coolant flow
through the heater core.
In some heater system designs, temperature control is achieved by
allowing part of the air moving through the heater duct system to bypass
the heater core. The amount of bypass air is controlled by a door. This
design is commonly called a blend air system. A water valve is sometimes
included in the design and directly linked to the door control.
Another cable operates a door inside the duct system and directs air
flow through defroster ducts to the windshield. The knob controlling the
blower motor switch may be set to one or more speed positions, or off. This
switch controls the air velocity (CFM) through the duct system and heater
core.
Note:
Air pressure, electric actuators or vacuum may be
used in place of cable controls. The air pressure or
vacuum do not automatically adjust system function.
Manual controls, air switches or other automatic electrical controls regulate vacuum and control air pressure to adjust system function.
Go to Chapter Start - Table of Contents - Index
5-7
Chapter 5 – System Controls
2. Vacuum Controls
Heavy trucks with diesel engines do not have a ready source of vacuum.
When vacuum components or controls are used, a separate vacuum pump
must be driven by the engine.
3. Passive (Automatic) Heater Controls
Various devices are used to control heater operation. These devices are
described below:
Water Valves
Some heater systems have an “H” type water valve design. Coolant
flows to and from the heater core through separate passages in the
valve. Means are provided to block coolant flow to the heater core
and bypass or route coolant back to the engine. A pressure valve in
the “H” opens when coolant flow to the heater is blocked. Figure 5-6
illustrates the “H” type coolant valve.
CAB HEATER
WITH PRESSURE RELIEF VALVE
INSTALLED WITH CABLE OPERATED
WATER VALVE IN SUPPLY LINE
Figure 5-6
RETURN
HEATER
WATER PUMP
INLET
WATER VALVE
CABLE OPERATED
This plumbing shows how
an “H” type water valve
may be used to allow coolant to flow through or to
bypass the heater core.
RETURN
SUPPLY
"H" VALVE
Heater A/C (CTC II™) & Heater (CTC™) Systems
The CTC™ (Constant Temperature Control) system maintains a
preselected temperature in the cab. This is accomplished through a
controllable circuit board and variable resistor. Changes in the air
temperature activate the circuit board, which energizes or
deenergizes an air solenoid valve. The solenoid valve controls the air
supply to open and close the water valve and pulse hot engine
coolant through the heater core. In the AC mode, the thermostat is
cycled to hold a constant output temperature. Figure 10-3 shows
how the CTC II™ components work together to control heat energy
movement into cab air and maintain cab temperature.
5-8
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HVAC Control Variations
HVAC Control Variations
Control variations include one, two or three speed blower/fan motor switches to
vary air velocity. Air or electrical toggle switches and rocker switches may be
used in system control to replace cable control. Air cylinders open or close duct
doors and radiator shutters. Air pressure hoses and fittings have a long service
life and are easy to repair. The following controls are discussed in this section:
1. Air Controls
2. Electrical Devices and Schematics
3. Combination and Supplemental Controls
4. Fan Clutches, Radiator Shutters, and Override Controls
1. Air Controls
The development of air controls has improved the operation and function
of HVAC systems. A basic form of air control may use a single switch and
cylinder to operate a duct door. In more complex systems air cylinders are
used to control fresh and recirculating air, heat/defrost and air conditioner vents. A pressure switch is often used to control the compressor
clutch.
The most common air control system is a modular design. Modular
units are simple and compact as illustrated in Figure 5-7. An air block
uses a pintle and programmed control lever to control air cylinders.
Figure 5-7
This cutaway view of an air
block shows the components
and describes their function.
The air cylinders are not
shown.
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RR
QQ
SS
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¢¢
TT
¤¤
¥¥
SS
TT
¤¤
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AIR FLOW
AIR BLOCK CLOSED
(CYLINDER VENTED)
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RR
,
Q
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,
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CONTROL LEVER
SPRING LOADED
PINTLES
AIR FLOW
O-RINGS
AIR FLOW
AIR BLOCK OPEN
In air control systems a Legris push-on fitting has gained popularity with
manufacturers. The Legris design speeds air tube installation and provides a positive leak free air seal where tubing is attached.
Some Frigidaire AC systems have a thermal limiter and superheat
switch combination to protect the compressor when system pressure is
too low. A low system pressure can mean there is not enough refrigerant
inside the system and/or insufficient refrigerant oil circulation to properly
lubricate the compressor. Figure 5-8 illustrates the function of the thermal limiter and superheat switch. When the fuse in the thermal limiter
melts, the clutch circuit is broken to stop the compressor. The thermal
limiter must be replaced when this happens.
Go to Chapter Start - Table of Contents - Index
5-9
Chapter 5 – System Controls
AMBIENT SWITCH
POWER IN
FUSE
HEATER
THERMAL LIMITER
Figure 5-8
This drawing shows a
Frigidaire thermal limiter
and superheat switch schematic. It works by interrupting the circuit
(electrical power) to the
clutch and stops the compressor.
GROUND
CLUTCH COIL
SUPERHEAT SWITCH
COMPRESSOR
There are a variety of other heat, air and pressure activated valves or
switches. These are shown in Figure 5-9 and described in the paragraphs
that follow.
LOW PRESSURE CUTOUT SWITCH–NORMALLY
OPEN, CLOSES AT 34 PSI, OPENS ON PRESSURE
DROP OF 10 PSI
HIGH PRESSURE CUTOUT SWITCH–NORMALLY CLOSED,
OPENS AT 350 PSI AND CLOSES WHEN PRESSURE
DROPS BELOW 250 PSI
Figure 5-9
Various types of heat, air
and pressure valves and
switches are illustrated.
HEAT SENSING SWITCH (CLAMPS TO TUBE) AS
HIGH TEMPERATURE SAFETY SWITCH, SET TO
OPEN AT 200° F
SOLENOID VAVLE–PROVIDES ELECTRICAL CONTROL
FOR OPERATING AIR CYLINDERS, AIR ACTUATED
SHUTTERS, AND AIR CONTROLLED CLUTCHING FANS.
THE VALVE CAN BE NORMALLY OPEN OR CLOSE
DEPENDING ON WHICH CONTROL PORT IS USED
A pressure relief valve may be installed on or near the compressor high
side or on the receiver-drier fitting. This valve “bleeds” excess refrigerant
pressure when malfunction or restrictions inside the system increase
pressure to dangerous levels.
A low pressure cutout switch may be installed in either the high or
low pressure side of the system. It is designed to sense low pressure due to
refrigerant loss or system restriction. It is wired into the clutch circuit,
and interrupts clutch operation to protect the compressor.
A low side low pressure switch is preferred, especially with axial
compressors having little or no oil storage capacity. A low side low pressure switch is much more sensitive to problems such as a blocked expansion valve or other situations involving a lack of refrigerant and oil
circulation.
High pressure cutout switches are frequently installed to protect
the compressor. They are positioned on the high side to sense pressure
inside the system, and are wired into the compressor clutch electrical
circuit. These switches complete the circuit to the clutch when “closed.”
They “open” when preset pressures are reached. Opening shuts the system down by breaking the circuit to the clutch.
5-10
Go to Chapter Start - Table of Contents - Index
HVAC Control Variations
Heat and air sensing switches and solenoids are some of the
other control devices used to open or close electrical circuits to control or
protect system components. These switches are frequently used as override controls in electric or air controlled engine fan and radiator shutter
applications.
2. Electrical Devices and Schematics
Relays and resistors are electrical controls. They are normally not
controlled by pressure or temperature except for the CTC™ system. A
relay is included in a circuit to divide power when the demand for it
exceeds the capacity of the control switch. A resistor is a voltage dropping
(or controlling) device used to control fan or blower speed. Variable
resistors are used to control temperature. Figure 5-10 illustrates a relay
and resistors.
Figure 5-10
An electrical relay and two
types of resistors are shown.
TWIN TEMP™ RELAY
RESISTOR FOR
THREE SPEED FAN
TEMPERATURE CONTROL RESISTOR
FOR CTC™ (CONSTANT
TEMPERATURE CONTROL) SYSTEM
Figure 5-11
This electrical schematic
shows how the rotary switch
(system on-off) is connected
to the thermostat and
blower motor assembly. The
condenser motor is wired to
the thermostat and
Trinary™ switches through
a relay. The resistor controls voltage to the blower
motor assembly.
The electrical schematic (wiring diagram) for a roof top air conditioner
shows how electrical components and controls are connected. The diagram used for Figure 5-11 is clear and easy to read. All major AC components in the refrigerant system are also shown. The wiring diagram and
AC part locations are not to scale.
CONDENSER
FAN MOTOR
TXV
EVAPORATOR
TRINARY™
SWITCH
BLOWER/
MOTOR
ASSEMBLY
RELAY
COMPRESSOR
CLUTCH
CONDENSER
MOTOR
RECEIVERDRiER
30 AMP
FUSED
CIRCUIT
ROTARY
SWITCH
THERMOSTAT
POWER IN
IGNITION
Go to Chapter Start - Table of Contents - Index
5-11
Chapter 5 – System Controls
3. Combination and Supplemental Controls
Combination and supplemental controls may protect the major components (primarily the compressor) from damage, control engine temperature and insure condenser efficiency.
When used in system design, combination and supplemental controls
help maintain the pressure and temperature balance inside air conditioner and heater systems. They can make safe system operation possible
in severe or varied climate conditions, and maximize heat energy movement under less than ideal conditions.
Two or three function pressure switch assemblies (Red Dot Binary™ or
Trinary™ switches) may be installed on the liquid side of the AC system
between the condenser and expansion valve. Both switches are illustrated
in Figure 5-12.
Figure 5-12
Red Dot Binary™ and Trinary™ switches with switch
operating pressures given.
RED DOT BINARY™ SWITCH
OPENS
CLOSES
Low pressure
protection
Between 3-15 PSIG
(falling pressure)
40 PSIG maximum
(rising pressure)
High pressure
protection
Between 270-330 PSIG
(rising pressure)
80-120 PSIG below
open pressure
RED DOT TRINARY™ SWITCH
OPENS
CLOSES
Low pressure protection
22.5 ± 7.5 PSIG
(falling pressure)
40 PSIG maximum
(rising pressure)
High pressure protection
Between 270-330 PSIG
(rising pressure)
80-120 PSIG below
open pressure
Shutter fan/override
Opens 35-60 PSIG
below closing pressure
200-230
PSIG (rising pressure)
The two function Binary™ switch prevents the compressor from operating if there is no refrigerant in the system. It also stops the compressor
if head pressures increase to unsafe levels. The switch resets when
pressure drops to normal.
Red Dot’s Trinary™ pressure switch performs three distinct functions to monitor and control pressure inside the AC system. The switch is
installed between the condenser and expansion valve, usually on the
receiver-drier. All three functions automatically reset when the proper
pressure is achieved.
• The low-range pressure function prevents compressor operation if the refrigerant charge has been lost or ambient temperature is too cold.
• A mid-range pressure function activates the engine fan clutch
or radiator shutter assembly. As system pressure reaches mid
range, the switch engages the fan clutch (fan motor on roof top
condenser units) and/or opens the radiator shutter. This increases air flow to the condenser and stabilizes or lowers
system operating pressures. The switch cycles on and off to
maintain operating pressures.
• A high-range pressure function turns off the compressor if
pressure is to high.
5-12
Go to Chapter Start - Table of Contents - Index
Chapter Review
• Multi function switches other than Red Dot’s are being used
in some applications. The concept is the same as described
above.
4. Fan Clutches, Radiator Shutters & Override Controls
An engine fan clutch and radiator shutter assembly may be used to
control and maintain engine (coolant) temperature. Engine fan and radiator shutter operation are closely related to radiator mounted AC condenser efficiency (heat energy movement). This is the main reason for fan
clutch and radiator shutter override controls.
There are three types of fan clutches:
• Viscous Drive
• Air Actuated
• Electric
All but the viscous type may have a fan override control as part of the AC
system. The viscous drive fan clutch has a high viscosity silicone fluid
that moves inside the clutch to increase or decrease fan speed. The fluid is
controlled by a temperature sensor, valve and centrifugal force.
Air actuated fan clutches are either on or off. Control is by a
thermostatic valve which measures engine coolant temperature. When
coolant is hot, the valve opens and air pressure enters the fan body
causing the clutch to engage. Some air actuated clutches use air pressure
for the off condition.
The electric fan clutch has a preset engine coolant temperature
sensor. When the set temperature is reached, the clutch is engaged for
increased air movement through the condenser and radiator. When coolant temperature drops the clutch disengages the fan.
Radiator shutters control air (outside air) flow through the radiator.
These shutters are opened and closed by thermal or air activated spring
loaded valves. Both types of valves sense and maintain engine coolant
within a narrow temperature range (4 to 6 degrees). The narrow 4 to 6
degree Fahrenheit temperature range selected may fall anywhere between 160 to 220 degrees Fahrenheit. Thus, override controls are required to bypass radiator shutter controls for efficient or safe condenser
function and AC system operation.
Chapter Review
• Basic system controls begin at a control panel inside the cab
or sleeper compartment. We can decide on heating or cooling
and where and how much air flow we want. We can select a
temperature range for the inside of the cab or sleeper.
• When a heater, air conditioner or HVAC system is turned on,
the automatic control devices take over system control. They
are designed to keep the system in balance and maintain the
operator selected temperature range inside the vehicle.
Go to Chapter Start - Table of Contents - Index
5-13
Chapter 5 – System Controls
• A balanced system is more efficient in moving heat energy
into or out of the air in the cab than an unbalanced one.
Balance means maintaining pressures and temperatures inside the system so that heat energy moves easily and efficiently from one area to another.
• In most systems one or more heat or pressure sensitive
switches may be installed. These usually protect the compressor if something goes wrong inside the system or the
refrigerant leaks out.
• The more advanced system designs use air pressure or
vacuum for system and component control. Electronic controls are also used. The advantages of advanced controls are
more even cab temperature and faster control response.
• The engine fan clutch and radiator shutter are controlled by
engine coolant temperature. In an AC system with an
underhood condenser, override controls are used to govern
fan clutch and radiator shutter operation.
5-14
Go to Chapter Start - Table of Contents - Index
Chapter
6
Click on any of these
subject headings to go
directly to the page
Service Tools and Their Use
• Safety & Safety Equipment
• Air Conditioning System Service Tools
• Other Equipment
• Chapter Review
The basic air conditioner and heater service tools include some special tools
and test equipment as well as normal tool chest items. In this section we
describe and explain the use of basic tools, test and other equipment, and
safety. Some of the special equipment described is expensive but is often
justified in a busy shop. Actual system test and service procedures are covered
in Chapter 8 and Chapter 10.
Safety is important to you as well as to others in your working environment.
The air conditioner and heater system are as safe or safer to work on as other
vehicle systems, engines, etc.—but they are a little different. We will stress
safety in this chapter and have used CAUTIONS and WARNINGS in bold
print all through the manual to alert you to potential hazards.
Safety & Safety Equipment
• In servicing HVAC systems you will be exposed to high pressures,
temperatures and several chemical hazards. Moving belts and pulleys
are normal shop hazards.
• In addition to exercising caution in your work, ALWAYS WEAR
SAFETY GOGGLES OR A FACE SHIELD when you are using
refrigerant or a Halide leak detector, adjusting service valves or the
manifold gauge set connectors. Safety goggles or a transparent face
shield are practical safety items. ONE OR THE OTHER IS ABSOLUTELY REQUIRED.
• Refrigerant inside a container and in parts of the AC system is a
liquid under pressure. When refrigerant escapes or is released to the
air, ITS TEMPERATURE DROPS INSTANTLY. If it spills on your
skin or in your eyes, flood the area with cool water and SEEK
MEDICAL ATTENTION IMMEDIATELY.
• The compressor creates pressure when it runs. If pressures get too
high in the system, the weakest point may separate or blow out. A
system restriction, too much refrigerant, or improper charging procedures are all potentially dangerous.
• Someone else may have serviced the system before you and put too
much refrigerant in the air conditioner. The only way to know how
much refrigerant is in the system is to take it all out. Then evacuate
the system and charge it with a weighed amount of refrigerant yourself, based on manufacturer specs. If too much refrigerant is in the
system for proper cooling, and you add more, you may have a potentially ruptured component and serious injury.
• Keep in mind the fact that R-12 refrigerant becomes a poison gas
when it burns. DO NOT SMOKE AROUND REFRIGERANT.
Go to Table of Contents - Index
6-1
Chapter 6 - Service Tools & Their Use
• Do not grab hold of a clutching fan to stop it when it is disengaged but
turning at low RPM. THE FAN CAN SERIOUSLY INJURE YOUR
HAND.
• Be sure the area you are working in has plenty of ventilation and that
no gas or other fumes are present. DO NOT USE A HALIDE LEAK
DETECTOR OR REFRIGERANT WITHOUT ADEQUATE VENTILATION. DO NOT RUN THE VEHICLE ENGINE DURING A
PERFORMANCE INSPECTION OR WHEN CHARGING THE
SYSTEM WITHOUT ADEQUATE VENTILATION.
WARNING
Fire or explosion hazards exist under certain conditions
with R-134a. A combustible mixture can form when air
pressures are above atmospheric pressure, and a mixture of air and R-134a exist. For this reason do not
pressure test air conditioning systems with compressed
air.
Air Conditioning System Service Tools
The basic AC tools that are discussed in this section include:
1. Recovery/Recycling Station
2. Refrigerant Dispensing Valves & Containers
3. Manifold Gauge Set
4. System Service Valves
5. System Service Valves
6. Vacuum Pumps
7. Leak Detectors
8. Flushing Kit
9. Heater System Service Tools
10. Other Equipment
1. Recovery/Recycling Station
The recovery/recycling station performs two closed loop processes. The
station removes the refrigerant from an AC system in the recovery
mode. The refrigerant is contained in an external cylinder for storing,
recycling, reclaiming, or transporting. Typically, the refrigerant is not
reusable until it is recycled. Contaminants in the refrigerant are reduced
in the recycle mode. The contaminants could include moisture, acidity,
and particulate matter. Chapter 9 contains more detailed information on
the recovery and recycle processes and necessary equipment.
Note:
6-2
Separate stations are required for R-12 and R-134a.
Go to Chapter Start - Table of Contents - Index
Air Conditioning System Service Tools
2. Refrigerant Dispensing Valves & Containers
Bulk containers should always be used with a scale or charging station
capable of measuring the refrigerant put into the system. Figure 6-1
illustrates the most common refrigerant container.
Figure 6-1
Refrigerant comes in a
standard size container and
may be dispensed with
single or dual dispensing
valves.
20 POUND CYLINDER
WARNING
All containers with refrigerant are under pressure (to
contain the refrigerant). Any heat will increase that
pressure. The containers are not designed to withstand excessive heat even when empty, and should
never be exposed to high heat or flame because they
can explode. Containers must be certified as meeting
DOT CFR Title 49 requirements.
There are several other tools that could be used when charging an AC
system with refrigerant. These are a charging meter (refrigerant scale) or
a charging station. They will be described later.
3. Manifold Gauge Set
The manifold gauge set is the tool used for internal system diagnosis and
service. A typical manifold has two screw type hand valves to control
access to the system, two gauges and three hoses. The gauges are used to
read system pressure or vacuum. The manifold and hoses are for access to
the inside of an air conditioner, to remove air and moisture, and to put in
or remove refrigerant from the system. Shutoff valves are required within
12 inches of the hose ends to minimize refrigerant loss.
Figure 6-2 illustrates a basic manifold gauge set and explains how it
works.
Manifold gauge sets are color coded. An R-12 gauge set normally has a
blue low side hose, a red high side hose, and a yellow or white utility
(center) hose. An R-134a gauge set will have a blue hose with a black
stripe for the low side, a red hose with a black stripe for the high side, and
a yellow hose with a black stripe for the utility (center) hose.
Different style end fittings are used on R-12 and R-134a hose sets. R-12
hose sets use a 1/4 female refrigeration flare (FFL) on all hose ends. A
shutoff valve is required on all three hoses within 12 inches of the end
connected to the AC system or service equipment. R-134a hose sets use a
1/2 ACME female nut on the gauge end. Special quick disconnect couplings are normally combined with a shutoff valve on the high and low
side hoses. The free end of the utility hose contains a 1/2 ACME female
nut and a shutoff device within 12 inches of the hose end.
Go to Chapter Start - Table of Contents - Index
6-3
Chapter 6 - Service Tools & Their Use
These special hoses and fittings are designed to minimize refrigerant loss
and to preclude putting the wrong refrigerant in a system.
Two hoses (left and right) connect to the low and high sides of the
system, usually at the compressor on R-12 systems. The center (utility)
hose is used to remove refrigerant from the system, evacuate air and
moisture, or add refrigerant. Gauges are calibrated for either high or low
pressure and vacuum. The term compound gauge set is often used because the low pressure gauge responds to pressure and vacuum. Separate
gauge sets are required for R-12 and R-134a.
LOW SIDE (SUCTION PRESSURE)
30
0
10
20
30
HIGH SIDE (DISCHARGE PRESSURE)
60
200
90
120
150
LOW
TEMPERATURE
300
100
400
0
500
HIGH
TEMPERATURE
VALVE CLOSED
VALVE OPEN
LOW SIDE
HAND VALVE
Figure 6-2
The basic manifold and
gauges are illustrated. The
low pressure gauge displays
pounds per square inch
(PSI) and inches of mercury
(in. Hg). Hg is the chemical
symbol for mercury. The
high pressure gauge reads
in pounds per square inch.
HIGH SIDE
HAND VALVE
TURN CLOCKWISE TO CLOSE
TURN COUNTER CLOCKWISE
TO OPEN
SERVICE HOSE & FITTING TO LOW SIDE
SERVICE HOSE & FITTING TO HIGH SIDE
UTILITY HOSE AND FITTING (FOR SYSTEM SERVICE)
CAUTION
Many gauges have dials with metric and US scales to
measure pressure. The more expensive manifold
gauge sets have liquid filled gauges and additional
valves and fittings incorporated in the manifold. All
gauges are breakable and should be handled with a
reasonable amount of care.
The high pressure gauge registers system pressure from 0 to 500 PSI. The
low pressure gauge registers pressure from 0 to 150 PSI clockwise, and
vacuum from 0 to 30 inches Hg counter-clockwise.
There are a few important rules and procedures you must follow
concerning gauge set hookup. Both the rules and procedure are for your
safety and to protect the AC system. The basic rules are covered briefly
here. Gauge set hookup should not be done until after you have made a
complete visual and performance inspection of all AC system components.
These inspections are described in detail in Chapter 7. In addition you
should inspect the engine, cooling system and other engine driven devices. Engine cooling system problems can cause false gauge readings and
incorrect AC system diagnosis. Worn drive belts or hoses are dangerous to
work around.
6-4
Go to Chapter Start - Table of Contents - Index
Air Conditioning System Service Tools
CAUTION
Never attempt to hook up the manifold gauge set with
the engine running. Never hookup the gauge set until
you have checked to be sure the hand valves on the
manifold are closed. Never hookup the gauges to the
AC system until you have made a visual and performance inspection.
Figure 6-3 shows the typical gauge set hookup location on a truck. Note
that the gauge set hoses are connected to system service valves.
Figure 6-3
This illustration shows the
typical manifold gauge set
hookup location.
COMPRESSOR SERVICE VALVE
(DISCHARGE SIDE)
COMPRESSOR SERVICE VALVE
(SUCTION SIDE)
MANIFOLD GAUGE SET
SUCTION HOSE
DISCHARGE HOSE
4. System Service Valves (R-12 Only)
System service valves allow safe access to the system inside of an AC
system through the manifold gauge set. There are usually two (2) service
ports mounted in an easily accessible area for access to the low and high
pressure sides of the system.
Two types of service valves are in common use today—stem type and
Schrader. The stem type valve stems screw in and out. They may be used
to isolate the compressor from the rest of the system for fast compressor
replacement. The Schrader type valve functions like a tire air valve. They
are easy to incorporate in other locations in the system. Figure 6-4 shows
both types of valves and how they work.
Note:
Many systems have extra service valves (Schrader) in
the system. These valves accommodate pressure
switches or provide another service port. The new
R-134a refrigerant uses special service fittings to prevent the mixing of refrigerants and oil.
Go to Chapter Start - Table of Contents - Index
6-5
Chapter 6 - Service Tools & Their Use
Figure 6-4
The valve drawings are
cutaway. The Schrader
valve in the upper portion of
the illustration (like a tire
air valve) is either closed or
open. The three illustrations
below show and describe
stem type valve positions.
SCHRADER TYPE VALVE
MANIFOLD GAUGE SET
HOSE CONNECTOR
VALVE
PIN IN CONNECTOR FORCES VALVE OPEN
BACK SEAT TYPE SERVICE VALVES
SERVICE PORT TO
GAUGE SET
AC SYSTEM PORT
TURN COUNTER CLOCKWISE TO OPEN
(BACKSEAT) FOR AC SYSTEM OPERATION
TURN CLOCKWISE TO CLOSE (FRONTSEAT)
TO ISOLATE THE COMPRESSOR
VALVE IN MID-SEATED POSITION
FOR SYSTEM SERVICE
5. System Service Valves (R-134a only)
New and unique service hose fittings have been specified for R-134a
systems. Their purpose is to avoid cross-mixing of refrigerants and lubricants with R-12-based systems. The service ports on the system are quick
disconnect type with no external threads. They do contain a Schrader type
valve as shown in figure 6-5. The low side fitting has a smaller diameter
than the high-side attachment.
QUICK CONNECT HOSE END FITTING
WITH INTEGRAL SHUTOFF VALVE
SERVICE HOSE CONNECTION
Figure 6-5
This illustration shows
R-134a service ports and
hose end fittings.
DEPRESSOR PIN
SYSTEM SERVICE PORT
VALVE ASSEMBLED TO SERVICE PORT WITH VALVE IN THE OPEN POSITION
6-6
Go to Chapter Start - Table of Contents - Index
Air Conditioning System Service Tools
6. Vacuum Pumps
Air and moisture inside an air conditioner contaminate the system. They
combine with refrigerant and refrigerant oil to form acid and sludge.
Moisture inside a system can freeze at the expansion valve orifice, blocking the flow of refrigerant temporarily. The result is erratic system function. A vacuum pump is used to remove air and moisture from the inside of
hoses and components of the air conditioner, but special care must be
taken to keep components clean and moisture free.
When the vacuum pump is hooked up to the system through the
manifold gauge set (and the service valves are open), the pump sucks air
out. The result is a negative pressure or vacuum. The air is removed
quickly, in just a few minutes. However, the humidity in the air may
condense inside the system and this moisture must be removed.
Moisture will vaporize in a vacuum when a sufficient vacuum level is
reached. Vacuum level is measured in inches of mercury. The vacuum
pump must operate long enough to cause any condensed moisture inside
to vaporize so the pump can suck it out of the system.
In truck and other heavy duty applications it is most difficult to remove
the moisture. The hoses used to connect the AC components in a truck
may be ten times longer than in a car AC system and may have more
bends and connections where moisture can hide. For this reason, vacuum
pump capacity and how long you use the pump are important. A higher
pump capacity and longer pumping time help insure that all moisture is
out of the system. There are two types of vacuum pumps, rotary vane and
piston type. They require an electrical source for power. Each is illustrated in Figure 6-6. The rotary vane pump is thought by many to be
superior because it is powerful and quiet. We will describe how to use a
vacuum pump to evacuate (remove air and moisture from) the system in
Chapter 8.
Figure 6-6
Two types of vacuum pumps
are illustrated and described. Both evacuate air
and moisture from the air
conditioning system through
the service valves, manifold
gauge set and hoses.
ROTARY VANE PUMP
TWO STAGE PISTON PUMP
7. Leak Detectors
There are two types of leak detectors in popular use. The least expensive
is called a Halide leak detector and is made from a propane torch. The
other is called an electronic leak detector. Electronic detectors operate on
one of two principals, positive ion or negative corona.
Go to Chapter Start - Table of Contents - Index
6-7
Chapter 6 - Service Tools & Their Use
Halide Leak Detector (R-12 Only)
A Halide propane torch leak detector can be used to find system
leaks as low as five ounces per year. It includes a propane tank and
torch assembly. The torch assembly includes a control valve and
tube, pickup hose, orifice at the top of the tube, and copper reactor
plate. A chimney surrounds the orifice and copper plate and has a
window cut out. The chimney shields the propane gas flame. You can
analyze flame color through the window.
In use, ignite the propane and adjust the flame to heat up the
reactor plate. The burning propane gas sucks air up the pickup tube
(the oxygen in the air also burns with the propane). To detect leaks,
move the pickup tube slowly about the AC system. Take care to move
the tube below potential leak points because R-12 is heavier than
the air. Any R-12 present is drawn up the tube and burned. When R12 is present in the flame, the copper reacts with it and the flame
changes color. Figure 6-7 illustrates this leak detector and method.
The flame colors are described.
HALIDE LEAK DETECTOR FLAME CONDITION (WAIT TILL REACTOR PLATE IS
CHERRY RED BEFORE CHECKING SYSTEM FOR LEAKS)
TORCH FLAME
AREA
CONTROL
VALVE
CLOSEUP OF CHIMNEY
COPPER REACTOR PLATE
PALE BLUE
NORMAL FLAME
Figure 6-7
The halide leak detector and
parts are described. You can
use it to detect R-12 leaks
as low as five ounces per
year. There are three drawings of chimney/reactor
plate/flame conditions to
show you how the detector
works to indicate a leak.
LIGHT GREEN/YELLOW
SMALL LEAK
PURPLE/BLUE/VIOLET
BIG LEAK
PICKUP HOSE
PROPANE TANK
WARNING
An open flame in your shop is dangerous. The Halide
leak detector should be used with care. Be sure there
is adequate ventilation to carry away any fumes from
the torch. Remember that refrigerant changes to a
poison gas when burned.
Electronic Leak Detector
Electronic leak detectors are safer than the Halide system and about
ten times more sensitive. Some designs can detect an R-12 or R-134a
leak as low as one half ounce per year. There are two types of
electronic detectors, positive ion and negative corona. These technical terms, positive ion and negative corona, are used in describing
the electronic elements and their function in these detectors. The
negative corona type detector has a longer service life and requires
less power.
6-8
Go to Chapter Start - Table of Contents - Index
Air Conditioning System Service Tools
Electronic detectors have a probe that is moved around the AC
system. Where refrigerant is present, a change in current flow inside
the probe is sensed by an electrical circuit. This activates a buzzer
which signals the user about the presence of a refrigerant leak.
Figure 6-8 shows an electronic leak detector of the negative corona
type.
Figure 6-8
The electronic leak detector
is a small hand held device
that is easy to use. It detects R-12 and R-134a leaks
as small as one half ounce
per year.
8. Flushing Kit
A flushing kit is used to remove contaminants from AC system hoses,
evaporator and condenser. Any other components should be bench
checked or replaced as flushing is either not effective or will cause damage. Flushing these components is recommended when you replace the
compressor or find contamination in other system components (receiverdrier, expansion valve, or at connections). Flushing must be done with a
"closed-loop" flushing kit using the Recovery/Recycle station.
Figure 6-9
Flushing kit to use with one
brand of recycling station
(Sercon).
9. Heater System Service Tools
In addition to normal tool box items, several test devices are required for
effective cooling system service. These are a pressure tester, hydrometer
and thermostat tester. The pressure tester is a simple hand pump with
a pressure gauge, hose, and adapters. The adapters are used to connect
the tester to the radiator filler neck or to the pressure cap. You use the
pump to apply pressure to the cooling system or cap. Then you check for
system leaks or for cap function.
A special cooling system hydrometer is used to draw coolant from
the radiator into a clear tube containing a float. The float has a scale you
read and relate to a scale on the hydrometer. The hydrometer scale
corresponds to a temperature level at which the coolant will freeze.
Go to Chapter Start - Table of Contents - Index
6-9
Chapter 6 - Service Tools & Their Use
A thermostat tester has a built in thermometer and a heating element.
You put water and the thermostat in the tester, turn on the heating
element and observe the thermostat to see if it functions. The thermostat
should begin to open at from three to nine degrees Fahrenheit below it’s
rated temperature and should be fully open at the rated temperature.
Other Equipment
The pulley alignment bar and belt tension gauge may already be a part of your
normal tool chest items. They are good tools to have for other service work. In
AC systems, belt alignment and tension are important for efficient compressor
clutch operation and belt and clutch bearing service life.
A fin comb is used to clean bugs and debris from the condenser and evaporator fins and straighten them if they are bent. These combs are made of molded
plastic with a series of grooves to correspond with condenser and evaporator fin
spacing.
The dial-type or digital thermometer is used to measure the temperature at
evaporator fins or the air coming out of ducts. Figure 1-6 in Chapter 1 illustrates and describes a typical dial type thermometer.
A variety of compressor service tool kits are available. These contain special
tools needed for clutch removal, compressor tear down, service and repair. To
check compressor oil level you can make your own oil dipsticks or purchase one
for each type of compressor. Three of these and their uses are illustrated in
Figure 6-10.
REAR OIL HOLE - TECUMSEH
Figure 6-10
3/16"
Refrigeration oil dipsticks
for checking compressor oil
levels are described in these
illustrations.
1"
30°
30°
/4"
3-1
OIL DIP STICK
3-1
/4"
6"
1/1
1/2" RAD
SIDE OIL HOLE – TECUMSEH
FINGER RING
NOTCH WIRE AS SHOWN
1/32 WIDE. (4) PLACES
YORK SIDE HOLE
50°
30°
4"
5-5/
8 RA
D
RA
D
3/
4-
COMPRESSOR POSITION
FOR SIDE HOLE OIL CHECK
5/
1"
16
78°
12 NOTCHES
1/8" APART
6-10
1-1/2"
Go to Chapter Start - Table of Contents - Index
" 8"
" 2" /8 -1/
32 /3 -7 1
9/ -7 1
2- 2
90°
45°
1-1/8"
Other Equipment
Compressor oil injectors are available that connect to the manifold gauge set or
charging station to dispense refrigeration oil.
It’s a good idea to have a torque wrench, a vacuum tester, a Schrader valve
core remover/installer and any other special system testers you would need if
you are going to service specific systems.
Earlier we mentioned refrigerant scales or charging meters and charging
stations. They are all designed to provide an accurate measure of the refrigerant you use when charging the AC system. The more elaborate charging
stations combine the refrigerant supply, manifold, gauges, a heated charging
cylinder, hoses and vacuum pump on an easily moved cart or stand. Some even
have refrigeration oil dispensing and leak detection capability built in. The
more expensive units have electronic controls. Figure 6-11 illustrates some of
these devices.
Charging Stations, Basic Description of Use
(Refer to Fig. 6-11.)
a. After repairing the AC system use this station to evacuate air
and moisture from it. The station adds the recovered/recycled
refrigerant to the AC system. A metering device is used in
conjunction with this station to monitor the amount of refrigerant added.
b. This all purpose recovery/recycling/recharging station provides all necessary service features in one package. This station recycles the refrigerant during the evacuation cycle. A
microprocessor control allows automatic recovery shutoff,
programmable evacuation and charging cycles.
Figure 6-11
Basic and electronically
controlled charging stations
and a charging meter are
pictured.
a.) CHARGING STATION WITH A
VACUUM PUMP AND CHARGING
CYLINDER
b.) ALL PURPOSE CHARGING STATION
INCLUDES AUTOMATIC EVACUATION,
OIL INJECTION, RECHARGING,
ELECTRONIC CONTROLS TO ADJUST
VACUUM PUMPING TIME AND LEAK
DETECTION
Other electronic devices you may want to consider are an electronic digital
thermometer or electronic sight glass. The advantage of the electronic thermometer is reading speed (it will give you a reading in a few seconds or less),
accuracy, and temperature range, all in one unit.
Note:
Separate charging stations are required for R-12 and
R-134a.
Go to Chapter Start - Table of Contents - Index
6-11
Chapter 6 - Service Tools & Their Use
The electronic sight glass is an ultrasonic device with two sensors. The sensors
are clamped to a metallic tube (not a hose) carrying refrigerant inside the
system, and connected to an electronic signaling device. The type of refrigerant
metering device used in the system and where you clamp the electronic sight
glass affect how the tester signals to tell you system charge condition.
Chapter Review
• Before servicing an HVAC system, safety must be taken into
account. Be aware of what safety precautions must be followed at
any time during the servicing of an HVAC system.
• Basic AC tools consist of a recovery/recycle station, refrigerant
dispensing valves and containers, a manifold gauge set, system
service valves, vacuum pumps, leak detectors, a flushing kit, and
heater system service tools.
• Other equipment used to service air conditioners includes a pulley
alignment bar, a belt tension gauge, a fin comb, a dial-type or
digital thermometer, a compressor service tool kit, a compressor
oil injector, a torque wrench, a vacuum tester, other special system testers, a refrigerant scale, a charging meter, a charging
station, and electronic devices such as electronic digital thermometers/pyrometers, and an electronic sight glass.
6-12
Go to Chapter Start - Table of Contents - Index
Chapter
7
Click on any of these
subject headings to go
directly to the page
Inspection and Maintenance–
without gauges
• Discussion of Inspection & Maintenance Survey Results
• Visual Inspection - System Off
• Electrical System Inspection
• Performance Inspection - Engine Running
• Heater System Inspection
• Preventive Maintenance Worksheet
• Chapter Review
Discussion of Inspection & Maintenance Survey Results
There are three reasons for regular inspection and maintenance procedures:
1. They save money in the long run by reducing down time and often
prevent more costly repairs.
2. They help to insure driver comfort and safety.
3. They add to your store of knowledge about these systems and
maintain your level of efficiency.
About half of all heavy duty vehicles have air conditioners. Surveys of AC
system owners find that over 30% of the systems are serviced every six months
or less, and another 62% are serviced at least once a year.
The survey also covered how often the different components required maintenance. Figure 7.1 below shows survey finding percentages. Failure of any of
the AC components listed in the survey could cause a system to malfunction or
stop cooling.
INSPECTION & MAINTENANCE SURVEY
Figure 7-1
This chart shows maintenance frequency, lists key
parts and how often they
require maintenance.
How often are your air conditioners serviced?
1 to 6 months
30%
Average
7 to 12 months
62%
More than 12 months
6%
Never
2%
Which AC components require frequent maintenance?
Belts
32%
Compressor Clutch
26%
Note:
Condenser
12%
Add Refrigerant
12%
Refrigerant Lines
11%
Valves
7%
The above survey results may not apply to your situation. Actual operating conditions for the vehicles you
service will determine or influence maintenance frequency and requirements.
The following inspection procedures should take about 15 to 20 minutes, longer
if corrective steps, part replacement or adding refrigerant is necessary. There is
a “Preventive Maintenance Worksheet” you may use at the end of this chapter,
Figure 7-9.
Go to Table of Contents - Index
7-1
Chapter 7 – Inspection & Maintenance
Visual Inspection - System Off
Your observations and the corrective measures you take may be different
depending on circumstances. The following inspection procedures are explained in more detail below:
1. Observe the System
2. Inspect Parts
3. Check Hoses and Fittings
4. Check for Refrigerant Leaks
Use the following procedures as a general rule in performing a visual inspection with the AC system off:
1. Observe the System
Your first inspection step is to answer the following question if you can:
• Has the vehicle just come in off the road and has the HVAC
system been in use?
• Did the operator or work order explain or describe any problems about the system?
• Did someone else work on the system yesterday, 700 miles
down the road? Your first inspection step is to answer these
questions if you can.
CAUTION
Even when someone has told you what is wrong with
an HVAC system, you should perform a visual inspection. Always make a visual inspection before you hook
up the manifold gauge set. Never add refrigerant to a
system until you have made a complete visual and
performance inspection.
2. Inspect Parts
Look at the system for what might come loose, leak, wear out or become
dirty and not function the way it should. The main points for visual
inspection of the system are emphasized in Figure 7-2.
7-2
Go to Chapter Start - Table of Contents - Index
Visual Inspection
Figure 7-2
This system illustration
notes the main points for
visual inspection.
CHECK ALL FITTINGS
& BENDS IN LINES FOR
LEAKS OR DAMAGE
CHECK COMPRESSOR
SHAFT SEAL AREA
FOR LEAKS (OIL)
CHECK COMPRESSOR
CLUTCH BRACKET &
MOUNTING BOLT
TENSION
CHECK BELT &
PULLEY ALIGNMENT
AND TENSION
CLEAN CONDENSER,
STRAIGHTEN FINS
CLEAN SIGHT GLASS
FOR VISUAL INSPECTION
A. Condenser – Is it free of leaves, bugs, bird feathers or mud? The
condenser must be relatively clean to work well as a heat exchanger.
How you clean the condenser depends on where it is mounted. The
condenser fin comb, air hose and nozzle, or soap and water may be
used. Where possible, check condenser mounting bolts or screws and
tighten them if necessary.
Condenser failure often results from loose hoses. Hose movement
will cause fatigue failure of condenser tubing adjacent to the fittings.
Make sure the hoses are securely clamped.
While inspecting the condenser check the receiver-drier sight
glass and connections. Look to see if the sight glass has a moisture
indicator that is showing moisture in the system.
B. Components Under the Hood – Tip the cab or raise the hood.
Look at the compressor mounting bracket, compressor clutch assembly, drive belt and pulley alignment. The mounting bracket, compressor, clutch and drive pulley should be fastened securely, and a
clutch groove (there may be two groves) should be in line with the
drive pulley. Tighten all bolts shown in Figure 7-3, as you inspect.
Figure 7-3
Engine and compressor
vibration can work mounting bolts loose. Tighten all
mounting bolts as you inspect the system. Slots in
the mounting bracket are
used to move the compressor clutch assembly in order
to adjust belt tension or
alignment.
Go to Chapter Start - Table of Contents - Index
7-3
Chapter 7 – Inspection & Maintenance
C. Drive Belt – The drive belt should be tight and in good condition.
Use a belt tension gauge to check tension (120 pounds maximum).
With experience, you can feel belt tension by twisting the belt. Try
feeling belt tension after using the gauge, when you know the
tension is correct. Replace belts if they are frayed or look worn.
If the clutch pulley/belt alignment is obviously off, you need to
loosen the compressor or mounting bracket, or both—and use the
alignment bar to line up the clutch pulley with the drive pulley.
Tighten compressor mounting bolts first, then the bolts holding the
bracket. The mounting bracket should have slots or other means of
adjustment to allow you to adjust the tension of the drive belt. When
you use a pry bar to apply tension, be sure you do not pry against the
compressor. Pry against the mounting bracket.
3. Check Hoses and Fittings
Check all hoses and fittings. Look for places where hoses flex when the
cab is tilted. Any places the hoses or fittings are fastened, clamped,
connected, bent or secured are potential wear points. This also applies to
places where hoses are not clamped or supported but should be (often
near the condenser). All of these spots are potential leak or damage
points. Tighten, re-fasten, add, or replace as indicated by your inspection.
4. Check for Refrigerant Leaks
System refrigerant leaks can be anywhere but there are obvious places.
You can spot some by looking for signs of refrigerant oil forced out with
refrigerant leakage. One location leaks frequently occur is the compressor
shaft seal. The shaft and seal are hidden behind the clutch assembly, but
centrifugal force will throw the oil off the shaft and against the engine,
bracket or whatever is close. Check these points when you examine the
compressor clutch and mounting bracket. A solution of soap and water
applied around potential leak points works well for detecting leaks. A leak
in the evaporator may be indicated if you feel around the condensate
drain hole and find oil present.
7-4
Note:
You can add inexpensive dry nitrogen gas to the system instead of R-12 if system pressures are low. Dispense the gas at no more than 200-250 PSI as this is
sufficient pressure to cause or indicate a leak point in
the AC system. AC service procedures for complete
system recovering of refrigerant, evacuating, and recharging are covered and illustrated in Chapter 9.
Note:
A leaking heater core could also result in coolant at
the condensate drain.
Go to Chapter Start - Table of Contents - Index
Electrical System Inspection
You can feel for oil at the bottom of all connections (see Figure 7-4) if the
system is not too hot. Of course, a few minutes with an electronic leak
detector is the best way to check for leaks. Keep in mind that pressure is
different in a system at rest, so small leaks may be hard to find. Pressure
in a system at rest, will equalize at from 60 to 95 PSI, depending on
outside air temperature. This means there is more pressure in the low
side of the system at rest than during normal system operation. Just the
opposite is true of the high side; at rest, high side pressure is lower. You
may want to use the detector to check for leaks in the high side when the
air conditioner is operating, if you suspect a leak and can’t find it when
the system is at rest.
Figure 7-4
This illustration shows a
potential refrigerant leak
point at the condenser
fitting.
Electrical System Inspection
The two stages of an electrical inspection are explained in more detail below:
1. Inspect Electrical Connections
2. Check Electrical Current Flow and Device Functions
Use the following procedures to perform an electrical system inspection:
1. Inspect Electrical Connections
First, while you are making your visual inspection under the hood (cab)
and/or at the roof top condenser, take a moment and check all electrical
connections visually and by feel. Look for any corrosion on leads or
connectors and clean them. Make sure all leads and wires are properly
supported and securely connected.
2. Check Electrical Current Flow and Device Functions
Perform the following steps to check current flow and electrical device
functions:
A. Turn the Ignition On – To check current flow the ignition must
be on.
Go to Chapter Start - Table of Contents - Index
7-5
Chapter 7 – Inspection & Maintenance
B. Turn the AC System On – This will power the thermostat and
clutch. If it does not come on, use the AC mode switch to check the
leads to the switch. You should be able to hear a “click” from the
thermostat and hear the clutch drive plate “snap” against the clutch
pulley. You can not check thermostat cycling on and off until you do
the performance inspection. Figure 7-5 illustrates a typical AC electrical system and the places you should inspect.
CONDENSER
FAN MOTOR
TXV
TRINARY™
SWITCH
BLOWER/
MOTOR
ASSEMBLY
RELAY
COMPRESSOR
CLUTCH
Figure 7-5
EVAPORATOR
CONDENSER
MOTOR
The electrical system inspection points are noted
with check marks (✔) on
this wiring diagram (electrical schematic).
RESISTOR
RECEIVERDRiER
ROTARY
SWITCH
30 AMP
FUSED
CIRCUIT
THERMOSTAT
POWER IN
IGNITION
C. Check Fuses – If there is a failure and you have made sure all
connections are clean and tight, you need to check fuses—in-cab as
well as in-line.
D. Check Clutch Engagement – Since you can’t see and may not
hear the clutch engage, get out and look at the clutch. If it’s engaged,
you will see that the drive plate is against the pulley and not slightly
spaced from it. If you are not sure the clutch is engaged, look for the
lead wire connector near the clutch. Break and close that connection.
The clutch will disengage and engage again.
E. Test Blower Speed Operation – Some systems have a common
switch that turns on the air conditioner and powers the blower
motor. Test blower speed operation by adjusting this or the separate
blower control switch. Feeling the air flow from the ducts or note
blower sound (speed) changes.
F. Inspect Roof Mounted Condensers – Don’t forget to inspect
roof mounted condensers and AC systems for dirt and debris. Be sure
the condenser fan(s) are working properly and all parts and electrical connections are securely fastened. The roof mounted condenser
fans may come on when the system is turned on. Like the thermostat
and most clutches, the normal on-off cycling action can not be
observed until the engine is running with the AC system on.
7-6
Go to Chapter Start - Table of Contents - Index
Electrical System Inspection
Performance Inspection – Engine Running
The purpose of visual and electrical inspection is to detect obvious problems
and assure AC system function for an accurate performance inspection. If you
do the performance inspection first, you could be mislead. Problem areas
discovered during the performance inspection can give you false clues or
symptoms, and result in repair errors and come-backs. The following performance inspection procedures are explained in more detail below:
1. Inspect System Component Cycling and Cab
Temperature Levels
2. Check Clutch Cycling Under Load
3. Check Sight Glass
The performance inspection does not cover pressure and temperature sensitive
safety devices (cutout switches, fan control, Trinary etc.). Testing these devices
requires the use of the manifold gauge set for observation of internal system
pressures during tests. These are explained in Chapter 8.
Use the following procedures as a general rule in a performance inspection:
1. Inspect System Component Cycling and Cab
Temperature Levels
A. Turn On the Engine and Air Conditioner – Inspect for system
component cycling and cab temperature levels.
Note:
System performance testing will be much faster
if all doors and windows in the cab are closed.
The cab air must cool down to thermostat control
setting levels before system components will cycle on
and off, indicating correct function. This is called
‘stabilizing the system’ and takes about five minutes
of operation. In very hot weather the system may not
cycle.
B. Check Thermometer Readings – In the cab you can use your
thermometer to measure air temperature at the vents. When the
evaporator is easy to reach with a thermometer probe without removing some of the dash or duct work, use the probe to measure
evaporator temperature. When the AC unit is on and working correctly, you can see the thermometer dial needle move down to about
32 degrees, then rise six to ten degrees and move back down again.
The movement up and down indicates that the cycling clutch and
thermostat, or orifice tube and accumulator pressure switch (to the
clutch) are functioning correctly. In systems with a non-cycling
clutch, this movement indicates correct function of the refrigerant
metering device.
The needle movement is called “temperature swing.” When you
can adjust the thermostat setting, the range of swing should change.
For example, from full cooling (cold) to moderate (between cold and
warm), the swing may change from 32-38 to 32-42 degrees.
Go to Chapter Start - Table of Contents - Index
7-7
Chapter 7 – Inspection & Maintenance
These readings at the vents will be higher and temperature swing
slower and not as obvious. Also blower speed will cause the temperature, levels to read higher (high air speed) or lower (low air speed) at
the same thermostat setting. When you measure air temperature, an
electronic thermometer/pyrometer is a great tool to have. You can
easily measure cab air temperature at several locations quickly.
Swing temperatures vary depending on where you measure temperature, and on outside temperature, humidity and altitude. The chart in
Figure 7-6, shows some examples of typical temperature variables. Don’t
forget that cab and sleeper area temperatures can vary within the same
vehicle. Also, electronic controls used in newer HVAC systems often keep
the temperature spread within a narrower range.
AIR TEMP.
DEGREES F.
AIR QUALITY
CENTER OUTLET
AIR TEMP.
DEGREES F.
70°
80°
90°
HUMID
DRY
HUMID
DRY
HUMID
43°
to
47°
40°
to
44°
44°
to
48°
40°
to
44°
47°
to
51°
Figure 7-6
100°
DRY
HUMID
40°
to
44°
DRY
52°
to
56°
41°
to
45°
LEFT
RIGHT
48°
to
55°
50°
to
56°
The chart of AC system and
cab temperature range
shows you typical variables.
LEFT & RIGHT AIR OUTLET TEMPERATURE WILL VARY
OUTLET AIR TEMP.
RANGE DEGREES F.
LEFT
RIGHT
LEFT
RIGHT
LEFT
40°
to
41°
41°
to
44°
41°
to
45°
43°
to
47°
46°
to
52°
RIGHT
47°
to
54°
2. Check Clutch Cycling Under Load
The following operating inspections, visual and by feel, are done outside
the cab while you wait for the system to stabilize.
A. Lift hood – With the hood up (or cab tilted) observe the clutch
cycling under load.
Note:
If the condenser is hood mounted you may not have
adequate air flow through it.
B. Touch suction and discharge lines – Soon after system start
up you can safely feel the suction and discharge lines and note their
change in temperature. The discharge line will get hot (after a while
it may be to hot to touch) and the suction line will get cooler.
3. Check Sight Glass
The sight glass is the only point where you can actually see inside the air
conditioner during operation. Check the sight glass through the window
on the top of the receiver-drier (or the separate in-line sight glass). If the
system is functioning properly and cooling the cab adequately, the sight
glass should be clear (you will not see anything in it). If it is not clear
when the system is first turned on, wait a few minutes for the system to
stabilize, then look again. Figure 7-7 illustrates and explains what you
may observe in the sight glass. Roof mounted condenser fans may run
continuously or cycle on and off. If you can’t tell by sound you may have to
climb a ladder and observe the fan blades.
7-8
Go to Chapter Start - Table of Contents - Index
Performance Inspection
SIGHT GLASS
Figure 7-7
• SYSTEM OK
These drawings illustrate
conditions you may observe
in the sight glass window.
CLEAR
• OVERCHARGE
• NO REFRIGERANT
• LOW ON
REFRIGERANT
FOAM, BUBBLES
OR MIST
• MAY BE AIR
IN SYSTEM
• A FEW INTERMITTENT
BUBBLES DURING
CLUTCH CYCLING
IS OK
• MAY BE LOW ON
REFRIGERANT
STREAKED
• MAY BE OIL STREAKS
AS OIL CIRCULATES
• DESSICANT
BREAKDOWN
CLOUDED
• CONTAMINATED
SYSTEM
Note:
A roof mounted condenser or AC unit assembly often
includes a roof mounted receiver-drier (and sight
glass) close to the condenser.
Heater System Inspection
A heater system inspection is really a combination engine cooling system and
heater inspection. All heater/cooling system rubber parts deteriorate due to the
air (ozone), heat, coolant and oils. They should be replaced at regular intervals
to prevent breakdown on the road. Metal parts and gaskets are subject to
malfunction or breakdown due to fatigue and corrosion.
Coolant has a limited life and should be replaced regularly. If it is dirty, the
cooling system should be drained and flushed or back flushed (using special
equipment) before refilling with clean water and anti-freeze. Coolant must be
hot when using the hydrometer to check protection (freeze-up) level. The
following inspection procedures are explained in more detail below:
1. Check Heater Control Valve Function
2. Inspect Other Functions
1. Check Heater Control Valve Function
Many air conditioner/heater systems depend on the heater control valve
for temperature control and positive closure. You can easily check heater
control valve function as follows.
A. Cool engine – Start with the engine cool, set the temperature to
cold and leave the fan off. As the engine warms up, feel the heater
return hose. If the hose feels warm or hot, the heater control valve is
leaking internally. This type of leak can seriously reduce air conditioning performance.
Go to Chapter Start - Table of Contents - Index
7-9
Chapter 7 – Inspection & Maintenance
B. Warm up engine – Next, let the engine warm up to normal
operating temperature and set both fan and temperature on high.
Feel both heater supply and return hoses. If there is a noticeable
difference in their temperature, it indicates a low flow of coolant
through the heater core (a partially closed or blocked heater control
valve). This could result in poor heating performance during cold
weather conditions.
HEATER SYSTEM CONTROL PANEL
HOT
TEMPERATURE
Figure 7-8
COOL
Heater/cooling system potential problem areas and
checks are indicated in this
drawing.
OFF
HEATER SYSTEM IN
CAB CONTROL
DEF
CAB
AIR DIRECTION
FAN
CHECK ALL HOSES
AND CONNECTIONS
FOR LEAKS, FRAYS,
AND WEAR
DEFROSTER VENTS
RADIATOR HOSE
HEATER CORE
TEST PRESSURE
RADIATOR CAP
CHECK COOLANT
LEVEL AND
APPEARANCE
BLOWER
ASSEMBLY
CHECK WATER
VALVE FUNCTION
FAN CLUTCH
WATER PUMP
CLEAN RADIATOR
OF DEBRIS
2. Inspect Other Functions
There are some things you can’t see or feel when you inspect the thermostat, heater core, radiator pressure cap, electrical switch and control valve
functions. Some of these can be checked with the pressure and thermostat
testers as described in Chapter 6. A hand pump pressure tester can also be
used to check for coolant leaks. This is done by using the pump to raise the
pressure inside the system above normal operating pressure to force
small suspected leaks to show up.
Heater/cooling electrical and valve component inspection is the same
as air conditioner inspection. The controls are operated to see if they
function correctly to maintain or vary cab temperature and air flow.
Preventive Maintenance Worksheet
Please feel free to modify or copy the worksheet in Figure 7-9. Actual vehicle
use, mileage, operating conditions and maintenance budget may influence
service frequency.
7-10
Go to Chapter Start - Table of Contents - Index
Chapter Review
Chapter Review
The purpose of these brief inspection procedures is for vehicle system maintenance and to determine if further, more detailed service is required. The uses of
a manifold gauge set, system troubleshooting, recovery, flushing, evacuating
and charging are explained in the next chapter.
High usage and operating condition variations are tough on air conditioning
and heater components. You should establish and follow regular inspection and
maintenance procedures to improve overall system function and component
service life.
The typical inspection should not take more than 15 to 20 minutes unless
component replacement and/or complete system evacuation and recharging is
warranted. The survey results shown in Figure 7-1, indicate belts, compressor
clutch assembly, condenser and the refrigerant lines are the most frequent
problem areas. However, your own experience with service and maintenance
may vary from survey results.
Inspection should first be visual and by feel. Some of your electrical system
inspection will be done as you inspect other components (checking leads,
connections and for loose wires). When you check the electrical circuit, begin
with the engine off but ignition on. A system performance inspection with the
engine running and system on really combines electrical and AC or heater
system function.
Go to Chapter Start - Table of Contents - Index
7-11
Figure 7-9 Preventive Maintenance Schedule.
PREVENTIVE MAINTENANCE SCHEDULE
FOR AIR CONDITIONING SYSTEMS
HEATERS AND
AIR CONDITIONERS
®
NOTE: Typical Maintenance Schedule: 3 months or 15,000 miles, 6 Months or 30,000 miles, 12 Months or 60,000 miles
Installation Date:
Mileage:
Last Maintenance Check:
Mileage:
Checked by
Mileage:
COMPONENT
MAINTENANCE
INTERVAL (months)
3*
6*
12*
COMPONENT
MAINTENANCE
INTERVAL (months)
DONE
1. COMPRESSOR
3*
6*
12*
DONE
•
❏
•
❏
•
❏
•
❏
4. EXPANSION VALVE
❏
❏
❏
❏
❏
•
•
•
•
•
Check noise level
Check clutch pulley
Check oil level
Run system 5 minutes
Check belts for tension
Inspect capillary tube
(leakage/damage/looseness)
5. EVAPORATOR
Clean dirt/bugs/leaves form
fins/tubes (w/compressed air)
(120 lb max.)
❏
❏
•
•
Inspect shaft seal (leakage)
Check mounting bracket
(tighten bolts)
Check solder joints on
inlet/outlet tubes (leakage)
Inspect condensate drain
❏
•
Check alignment to clutch
(R-12 or oil leak)
w/crankshaft drive pulley
•
•
Perform manifold gauge check
Verify clutch is engaging
❏
❏
6. OTHER COMPONENTS
Check discharge lines
•
❏
•
❏
(hot to touch)
Check suction lines
CONDENSER
2. Clean dirt/bugs/leaves from
❏
•
•
Inspect fittings/clamps/hoses
coils (w/compressed air)
Check inlet/outlet for
(cold to touch)
❏
•
obstructions/damage
•
Check thermostatic switch
(proper operation)
Outlets in cab (temperature
❏
•
condenser (hot to touch)
Check sight glass
•
❏
•
❏
•
❏
check; 40 to 50°F)
RECEIVER-DRIER
3. Check inlet line from
Check fan clutch (proper
operation)
•
❏
Inspect all wiring
❏
Operate manual controls
connections
(streaks or cloudiness)
•
Replace if system is opened
•
through full functions
The following require monthly maintenance:
*Compressor – run system at least 5 minutes (40 degrees Fahrenheit minimum outside temp.) in order to circulate oil and lubricate components.
Maintenance notes:
7-12
❏
❏
Go to Chapter Start - Table of Contents - Index
❏
Chapter
8
Click on any of these
subject headings to go
directly to the page
Troubleshooting
& Service Procedures
• Troubleshooting Overview
• Understanding System Function
• A Troubleshooting Example
• Manifold Gauge Set Installation
• Troubleshooting by Manifold Gauge Set Readings
• Review of Frequent Problem Areas
• Conclusion
Can you fix an air conditioner or heater system without finding and
correcting the cause of the problem? You bet you can! It happens every
day and it’s not good for business. Here is an example. A truck pulls in off the
road and the operator asks to have his rig serviced in a hurry. He tells you the
air conditioner isn’t cooling like it should and dashes into the restaurant for
lunch.
You tip the hood, and check the sight glass on top of the receiver-drier. You
see bubbles, not a lot but a fairly constant stream of them. It is obvious the
system is low on refrigerant so you hook up the manifold gauge set, purge the
gauge set hoses of air, and add refrigerant until the sight glass clears. Then you
check evaporator temperature and it’s OK. The air conditioner is repaired
right? Wrong! What you did is add refrigerant and the problem went away. You
did not find and fix the cause of the problem.
Component failure in an air conditioning system may be the result of a
problem elsewhere in the system. For example, a belt or clutch failure might be
caused by a dirty condenser restricting air flow and increasing head pressures.
High head pressures commonly create problems with other system components. Take time to look beyond the obvious for a potential hidden
problem.
Troubleshooting Overview
Troubleshooting includes collecting enough information to locate the cause of
the problem, then correcting the problem and its cause by replacement, adjustment, and/or repairing. You begin by gathering information from the most to
the least important sources.
Starting with the most important:
1.
2.
3.
4.
Your personal knowledge and experience with AC systems.
The vehicle operator's knowledge and experience—question him or her.
The work order.
Good test equipment and the HVAC system
The routine you follow when troubleshooting should proceed from the most to
least productive way of locating the problem and fixing the cause.
Go to Table of Contents - Index
8-1
Chapter 8 – Troubleshooting & Service Procedures
Experienced troubleshooters talk to the operator if they can, then personally
verify the symptoms of the problem whenever possible. They attempt quick
fixes on the basis of their knowledge of common system problems and causes
when appropriate. They know where components are located, and make repairs when they have a good idea of what the problem is. They fix the cause or
causes as well as the problem. They are confident of their knowledge and
ability.
Note:
The best troubleshooters all know who to call
when they get stuck. They know someone who
knows more than they do and are not too proud to ask
for help or suggestions when needed. The key—understanding system function
The Key–Understanding System Function
Your complete understanding of AC and heater systems and how they
work, plus what can go wrong, is the key to troubleshooting and
repair. We have talked about components and system function before. Now
let’s take a little different approach in describing what happens when the air
conditioner is turned on. In Figure 8-1 we have used numbers on the illustration to track normal air conditioner function.
Figure 8-1
An illustration of the typical
HVAC system. The numbers
follow the action when the
AC part of the system is
working properly (moving
heat out of the cab and into
the outside air).
CONTROL PANEL
1
BLOWER AND MOTOR
2A
3
5
EVAPORATOR COIL
AND THERMOSTAT
2
4
FAN CLUTCH
11
AC EXPANSION VALVE
AND CAPILLARY TUBE
10
COMPRESSOR &
CLUTCH ASSEMBLY
7
6
SIGHT GLASS
RECEIVER-DRIER
9
8-2
RADIATOR MOUNTED
CONDENSER
8
Go to Chapter Start - Table of Contents - Index
Understanding System Function
When you turn on the air conditioner at the control panel (1), the thermostat
(2), is supposed to sense a warm temperature at the evaporator. A circuit in the
thermostat should close, allowing current to flow through the thermostat to the
compressor clutch field coil (3). When this happens, the clutch field coil becomes an electromagnet and pulls the clutch drive plate (4) tight against the
clutch pulley (5).
Note:
The same AC switch (1) may also turn on the fan or
blower motor (2a) to circulate air in the cab. The air
feels warm at first but will cool quickly.
A belt connects the clutch pulley to a drive pulley (6) on the engine. The engine
provides the power to turn the clutch pulley and drive the compressor (7) when
the clutch is engaged. When operating, the compressor compresses and pushes
refrigerant gas to the condenser (8), through the receiver-drier (9), and to the
expansion valve (10) orifice. When it does, it puts a lot of pressure on the gas.
The compressor raises the temperature and pressure of the refrigerant inside
the high side of the system.
At the same time, the compressor is also sucking in low pressure refrigerant
gas from the expansion valve orifice, evaporator and through the low side of the
system. The movement of the refrigerant inside the system transfers heat
energy from the cab to the outside air for occupant comfort.
The automatic functions of the thermostat (or the pressure valve on some
accumulators), and the expansion valve, help maintain pressures and temperatures inside the system at safe and efficient operating levels. Pressure and
temperature are constantly changing due to compressor and expansion valve
action, the amount of heat energy being moved and the environment or
weather conditions.
The engine cooling system fan and clutch (11), and the evaporator blower
motor (2a), move a sufficient amount of air through the condenser and evaporator. On the road, vehicle speed provides most of the (ram) air required for the
condenser to work right. In a parked or slow moving vehicle the engine fan (or
roof or remote mounted condenser and fans) moves sufficient air through the
condenser fins.
Note:
Clean refrigerant and refrigeration oil should be inside the system in the amount specified by the manufacturer. Moisture, sludge (moisture combined with
refrigerant oil or desiccant), or desiccant particles
will prevent the correct performance of the system
and may cause component damage.
A Troubleshooting Example
Remember the story at the beginning of this chapter? The vehicle operator
pulled in off the road and asked you to repair the rig. He was in such a hurry he
didn’t tell you anything except that the air conditioner wasn’t cooling. Here is
the best way to handle that kind of situation.
Go to Chapter Start - Table of Contents - Index
8-3
Chapter 8 – Troubleshooting & Service Procedures
Use your knowledge and experience. Ask yourself what could have caused a
lack of cooling in that rig! Did the compressor drive belt break? Did a pressure
switch or relief valve cutout the compressor because of high or low system
pressure? Does the switch or valve in this type of system reset itself? Could
there be a superheat switch and thermal limiter with a melted fuse. Did
someone else service the system recently and put in too much refrigerant?
Could there be contaminants in the system blocking the expansion valve
(expansion tube)? If there is a leak, why and how did refrigerant get out of the
system? You know if refrigerant can get out, air and moisture may get inside as
well, especially if the leak is on the suction side of the system. Could there be a
restriction to refrigerant flow in one of the high pressure lines because of a
kink? From your knowledge and experience, you already know about these
possibilities and others when you talk to the operator (before he has the chance
to leave).
The right kind of questions can speed up troubleshooting and your service
work by pinpointing the problem(s) that needs fixing. Your conversation with
the operator might be as follows:
• How long ago did the AC system stop cooling?
Answer: About an hour ago.
• What steps did you take when you noticed the lack of
cooling?
Answer: I put it on maximum cool.
• Then what did you do?
Answer: When it wouldn’t cool, I opened the window and
turned the air conditioner off.
• Is this problem new or has it happened before, and when?
Answer: In the last few days I’ve had problems with
cooling off and on—this is the first time it’s happened when
I was close to a place that did AC service.
• Do you get any cooling at all?
Answer: Yes but it seems to quit after a while.
• Do you still get air flow at the vents from the blower?
Answer: Yes.
• When was your air conditioner checked thoroughly?
Answer: Before I bought the rig last May (a year ago).
• Has the heater been used recently and did it work OK?
Answer: Yes.
8-4
Go to Chapter Start - Table of Contents - Index
A Troubleshooting Example
• Have you had other service problems in the last few
months?
Answer: No.
• (If the answer was yes, you should ask—When? Where?
What was fixed or replaced?).
• Finally, ask the operator if he or she has a wiring diagram
for the system.
Now let’s look at the information you have gathered from the operator and
what you know from experience. He believes the problem is that the AC system
quits cooling after it has been on for a while! You know that the AC system has
not been maintained since the rig was purchased a year ago. Because of that,
there could be several causes for the problem (lack of cooling) and there may be
other potential problems about to develop.
It is possible that some refrigerant has leaked. Moisture and other contamination may be inside the system. You have been told there are no heater
problems, but that doesn’t mean there are none that might affect AC system
operation. The AC system has quit cooling several times in the last few days.
The problem may have become more severe than when it quit cooling the first
time.
If enough refrigerant or oil has leaked out, a low pressure cutout switch may
have cut the circuit to the clutch, protecting the compressor. Because the
system has not been maintained in a year, there may be other components that
should be serviced. You could fix the probable causes, and the system might
work and then break down again as the rig drives out of your place. From your
knowledge and what the operator has just told you, you know this may not be a
quick fix problem.
It’s up to you to describe the service situation to the operator. Tell him you
need to do a complete system maintenance inspection to find and correct the
problem or other potential problems. He can give you the go ahead for full
service and repair now, wait till you have inspected the system to determine
cause and cost, or delay repair until he has some down time available.
Normally when the operator can tell you what the problem is, you would first
operate the system to verify the problem. In this situation your troubleshooting
(your own knowledge added to what the operator told you), indicates the next
step. You need to do a complete maintenance inspection instead! Proceed as
described in Chapter 7. Correct any obvious problems and check carefully for
leaks. Leak testing should be visual, by feel and with a leak detector. Next, do
your performance test with the engine running and the AC system on.
Note:
Don’t forget to check the heater system too! If the
water valve is not closed, then hot engine coolant
flowing through the heater core would warm the air
at the same time the evaporator was trying to cool it.
The result would be the appearance of an AC problem.
Go to Chapter Start - Table of Contents - Index
8-5
Chapter 8 – Troubleshooting & Service Procedures
If your AC and heater visual, electrical and leak inspections don’t turn up any
problems, save time by hooking up the manifold gauge set before you make the
performance test. If you find a leak and can correct it easily by tightening a
connection, do so. But if too much refrigerant leaked out, you may have to add
some refrigerant to the system for an effective performance test. We will get
into detail on troubleshooting with gauges after we explain manifold gauge set
installation and adding refrigerant.
Manifold Gauge Set Installation
CAUTION
Never hook up the gauge set when the engine and air
conditioner are running. Be sure all the valves on the
manifold are closed all the way (turn them clockwise).
Check the hose connections on the manifold for tightness.
Locate the low and high side system service fittings and remove their protective caps. Position or hang the manifold gauge set in a convenient location.
Figure 8-2 illustrates a good example of manifold gauge set hookup in one
service situation.
Figure 8-2
A typical manifold gauge set
hookup is shown in this
illustration. The center hose
on the gauge set is connected to the vacuum pump.
The manifold gauge set is a necessary tool in troubleshooting AC system
problems. The following steps are performed during and after installing the
manifold gauge set:
1. Purging Air from the Gauge Set Hoses
2. Adding Refrigerant to the System
3. Stabilizing the AC System.
8-6
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Installation
1. Purging Air From Gauge Set Hoses
Environmental regulations require that all service hoses have a shutoff
valve within 12 inches of the service end. These valves are required to
ensure only a minimal amount of refrigerant is lost to the atmosphere. R12 gauge set hoses have a valve near the end of all three hoses. R-134a
gauge sets have a combination quick disconnect and shutoff valve on the
high and low sides. The utility (center) hose also requires a valve.
The initial purging is best accomplished when connected to recovery or
recycle equipment. Figure 8-3 illustrates the gauge set connections for
purging and refrigeration recovery.
LOW SIDE
Figure 8-3
HIGH SIDE
30
0
10
20
30
The purging setup for manifold gauge set and compressor service valves are shown
here.
60
90
120
150
LOW
TEMPERATURE
200
300
0
500
100
400
HIGH
TEMPERATURE
FROM EVAPORATOR
TO RECOVERY
STATION
TO CONDENSER
SHUTOFF
VALVE
OPEN 1 1/2 TURNS
(IF EQUIPPED WITH
STEM-TYPE SERVICE
VALVES)
COMPRESSOR
Note:
The manifold gauges read system pressure when the
hand valves are closed if the hose end valves, and the
stem type service valves (if included) are open.
2. Adding Refrigerant to the System
Now that the gauges are connected, you may need to add some refrigerant
to the AC system before you can do an effective performance inspection.
However, if leaks are obvious they should be repaired prior to adding
refrigerant.
Note:
Loss of some refrigerant is not unusual over an extended period of time. Adding refrigerant is a typical
procedure when the AC system is maintained on a
regular basis.
When adding refrigerant to the system, connect the center hose from the
manifold gauge set to the refrigerant dispensing valve on the container.
Figure 8-4 illustrates this connection.
Go to Chapter Start - Table of Contents - Index
8-7
Chapter 8 – Troubleshooting & Service Procedures
LOW SIDE
GAUGE
30
0
10
20
30
60
120
150
LOW
TEMPERATURE
SHUTOFF
VALVE
OPEN
200
90
HIGH SIDE
GAUGE
300
100
400
0
500
HIGH
TEMPERATURE
HIGH SIDE:
KEEP HAND
VALVES CLOSED
LOW SIDE:
KEEP HAND
VALVES CLOSED
Figure 8-4
In this illustration we have
noted how refrigerant is
added to the air conditioner.
LOW SIDE HOSE
(FROM EVAPORATOR)
HIGH SIDE HOSE
(TO CONDENSER)
STEM-TYPE VALVES
(IF USED)
MID-POSITION
TANK
VALVE
OPEN
REFRIGERANT TANK
COMPRESSOR
Before adding refrigerant to the system you should study the sight glass
while the engine is running and the air conditioner is on. Even if you
found a leak during the system inspection and corrected it, you have no
way of knowing how much refrigerant has leaked. You will not be able to
tell how much refrigerant is in there, but you can see if bubbles are
present.
Then check the gauges for unusually high or low readings, or a lack of
pressure. Following this procedure, and using your knowledge and experience, decide if it is safe and makes sense to add refrigerant in order to
make your full performance inspection.
You are now ready to add refrigerant to the system. For your safety and
to prevent system damage use the following procedure.
1. Turn on the engine and set the idle at 1200 to 1500 RPM and
then turn on the air conditioner.
CAUTION
Do not open the high pressure hand valve on the
manifold gauge set. The compressor could pump refrigerant into the container and cause it to BURST.
Be sure to keep the refrigerant container upright to
prevent liquid refrigerant from entering the compressor.
2. Open the refrigerant dispensing valve on the container and
then the low pressure hand valve on the manifold. This allows
refrigerant to enter the system as a gas on the low pressure or
suction side of the compressor. The compressor will pull refrigerant into the system.
8-8
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Installation
3. Add refrigerant until the gauges read in the normal range and
the sight glass appears clear. The sight glass may not be clear
for a moment just before or after the clutch cycles on and off
but should generally be clear. Gauge readings will fluctuate
as the compressor cycles on and off.
Note:
CAUTION
Pressures within the air conditioning system vary
with ambient temperature. A normal pressure range
is defined as follows:
Low side
15–30 PSIG
High side
150–280 PSIG
If R-134a is used in place of R-12 the high side readings
will be about 20 PSI higher. For this reason many
OEMs are recommending an increase in condenser capacity when retrofitting to the new refrigerant, R-134a.
If the gauges show any abnormally high or low pressures as you are adding refrigerant, stop and investigate for probable cause. Never add more than one
pound of refrigerant. If the system is low enough on
refrigerant to require more than that amount you
should stop and check again for leaks. Then recover
all of the refrigerant, repair, evacuate and recharge
the air conditioner. (See Chapter 9). You may want to
add dry nitrogen gas to the AC system instead of R-12
if pressures are below normal and a leak is suspected.
Nitrogen gas is sold in cylinders under high pressure,
1800 to 2000 PSI. Be sure the cylinder has a pressure
regulating valve to control the pressure when dispensing nitrogen gas. Dispose the gas at no more than
200-250 psi, as this is sufficient pressure to cause or
indicate a leak point. See note under Troubleshooting
by Manifold Gauge Set Readings in this chapter.
4. When the gauges show normal, close the hand valve on the
manifold, the hose end shutoff valve, and the valve on the
refrigerant container. You can now proceed with the performance inspection.
3. Stabilizing The AC System
For reliable gauge readings as an aid in troubleshooting, the AC system
must be stabilized.
CAUTION
Be sure your tools and test equipment are clear of all
moving parts of the engine and air conditioner.
Go to Chapter Start - Table of Contents - Index
8-9
Chapter 8 – Troubleshooting & Service Procedures
Start the engine and set to a fast idle of 1200 to 1500 RPM. Turn on the air
conditioner. After a quick in-cab performance test of control function,
blower speeds and air flow, set the AC system controls to maximum
cooling and blower speed on high. All windows must be closed. If cab
temperature is hot (rig has been sitting in the sun with the windows
closed), open the windows for a minute or so to let the hot air out. Run the
engine and air conditioner about five minutes for the system to stabilize.
In hot humid weather or where the AC condenser can’t receive adequate
air flow from the engine fan you may have to use a floor mounted fan to
force sufficient air flow through condenser fins. This helps to stabilize the
system by simulating ram air flow found under normal operating conditions.
When a vehicle has a tilt cab or hood and the condenser is part of the
grill, you must use the floor fan to get air to the condenser. You could tilt
the cab or hood back to normal position, carefully routing the manifold
gauge set and hoses away from moving parts. Then place the gauges so
you can read system pressure.
Troubleshooting by Manifold Gauge Set Readings
The series of figures that follow (Figures 8-6 through 8-15) show gauges with
typical readings indicating AC system problems. Each figure is followed by
troubleshooting tips, probable causes for the gauge readings shown, and appropriate service and repair procedures.
Low Refrigerant Charge in the System
30
LOW SIDE LOW
0
10
20
30
Figure 8-5
Gauge reading, low refrigerant charge in the system.
60
200
90
120
150
LOW
TEMPERATURE
300
100
400
0
HIGH SIDE LOW
500
HIGH
TEMPERATURE
Tip:
You see bubbles in the sight glass. The air from
vents in the cab is only slightly cool.
Cause:
Insufficient refrigerant (charge) in the system.
8-10
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Readings
Repair Procedure:
Check for leaks with your leak detector. If you
find a leak at a connection, tighten it then add
refrigerant as necessary. If a component or line
is leaking (defective), recover all refrigerant
from the system. Replace the defective part and
then check the compressor oil level and replace
missing oil. Evacuate and recharge with refrigerant, then check AC operation and performance.
Figure 8-6
Gauge reading, extremely
low refrigerant charge in
system.
Extremely Low Refrigerant Charge in the System
30
LOW SIDE LOW
0
10
20
30
60
200
90
120
150
LOW
TEMPERATURE
300
100
400
0
HIGH SIDE LOW
500
HIGH
TEMPERATURE
Tip:
The sight glass is clear or shows oil streaks. The
air from vents in the cab seems warm. If there is
a low pressure or Trinary™ switch in the system
it may have shut off the compressor (clutch).
Cause:
Extremely low or no refrigerant in the system.
There is a leak in the system.
Repair Procedure:
Add refrigerant to the system, at least half of the
normal full charge amount. Then perform your
leak test. As an alternative to a refrigerant, add
dry nitrogen gas to the system and then test for
leaks.
Note:
It may be necessary to use a jumper wire to
bypass some types of low pressure cutout
switches to operate the compressor (clutch)
when you add refrigerant to the system.
Go to Chapter Start - Table of Contents - Index
8-11
Chapter 8 – Troubleshooting & Service Procedures
After finding a leak, recover all refrigerant from
the system and repair the leak. Check the compressor and replace any refrigeration oil lost due
to leakage. Evacuate and recharge the system
with refrigerant, then check AC operation and
performance.
Air and/or Moisture in the System
30
0
10
20
30
LOW SIDE NORMAL
Figure 8-7
Gauge reading, air and/or
moisture in the system.
60
90
120
150
LOW
TEMPERATURE
200
300
0
500
100
400
HIGH SIDE NORMAL
HIGH
TEMPERATURE
Tip:
The sight glass may be clear or show some bubbles.
The air from vents in the cab is only slightly cool.
In a cycling clutch type system with a thermostatic
switch, the switch may not cycle the clutch on and
off, so the low pressure gauge will not fluctuate.
Cause:
Air and/or moisture in the system.
RepairProcedure:
Test for leaks, especially around the compressor
shaft seal area. When the leak is found, recover
refrigerant from the system and repair the leak.
Replace the receiver-drier or accumulator because
the desiccant may be saturated with moisture
(there is no way to tell). Check the compressor and
replace any refrigeration oil lost due to leakage.
Evacuate and recharge the system with refrigerant, then check AC operation and performance.
8-12
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Readings
Excessive Air and/or Moisture in the System
Figure 8-8
Gauge reading, excessive air
and/or moisture in the
system.
30
LOW SIDE HIGH
60
200
90
0
10
20
30
120
300
100
150
400
0
LOW
TEMPERATURE
HIGH SIDE HIGH
500
HIGH
TEMPERATURE
Tip:
There may be occasional bubbles in the sight glass.
Air from vents in the cab is only slightly cool.
Cause:
System contains excessive air and/or moisture.
Repair Procedure:
Test for leaks, recover refrigerant from the system and repair the leak. Depending on the type
of system, replace the receiver-drier or accumulator. The desiccant is saturated with moisture.
Check and replace any compressor oil lost due to
leakage. Evacuate and recharge the system,
then check AC operation and performance.
Expansion Valve (TXV) Stuck Closed or Plugged
Figure 8-9
Gauge reading, expansion
valve (TXV) stuck closed.
30
LOW SIDE LOW OR VACUUM
0
10
20
30
60
120
150
LOW
TEMPERATURE
Tip:
200
90
300
100
400
0
HIGH SIDE HIGH
500
HIGH
TEMPERATURE
Air from vents in the cab is only slightly cool.
The expansion valve body is frosted or sweating.
Go to Chapter Start - Table of Contents - Index
8-13
Chapter 8 – Troubleshooting & Service Procedures
Cause:
Test:
An expansion valve malfunction could mean the
valve is stuck in the closed position, the filter
screen is clogged (block type expansion valves do
not have filter screens), moisture in the system
has frozen at the expansion valve orifice, or the
sensing bulb is not operating. In vehicles where
the TXV and sensing bulb are accessible, perform the following test. If not accessible, then
proceed to Repair Procedure.
1. Warm diaphragm and valve body in your hand or
carefully with a heat gun. Activate system and
watch to see if the low pressure gauge rises.
2. Next, carefully spray a little nitrogen, or any
substance below 32 degrees Fahrenheit, on the
capillary coil (bulb) or valve diaphragm. The low
side gauge needle should drop and read at a
lower (suction) pressure on the gauge. This indicates the valve was part way open and that your
action closed it. Repeat the test, but first warm
the valve diaphragm or capillary with your
hand. If the low side gauge drops again, the
valve is not stuck.
3. Clean the surfaces of the evaporator outlet and
the capillary coil or bulb. Make sure the coil or
bulb is securely clamped to the evaporator outlet
tube and the insulation is in place. Next proceed
with recovering refrigerant from the system.
Repair Procedure:
Inspect the expansion valve screen (except block
type valves). To do this you must recover all
refrigerant from the system. Disconnect the inlet
hose fitting from the expansion valve. Remove,
clean and replace the screen, then reconnect the
hose. Any signs of contamination will require
flushing the system. Next, replace the receiverdrier. Then evacuate and recharge the system
with refrigerant, and check AC operation and
performance.
8-14
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Readings
Note:
If the expansion valve tests did not cause the
low pressure gauge needle to rise and drop,
and if the other procedures described did not
correct the problem, the expansion valve is
defective. You must recover all refrigerant
from the system again, and replace the expansion valve and receiver-drier. Evacuate and
recharge the system with refrigerant, then
check AC operation and performance.
Expansion Valve (TXV) Stuck Open
Figure 8-10
Gauge reading, expansion
valve (TXV) stuck open.
30
LOW SIDE HIGH
0
10
20
30
60
90
120
150
LOW
TEMPERATURE
200
300
0
500
100
400
HIGH SIDE NORMAL
HIGH
TEMPERATURE
Tip:
Air from vents in the cab is warm or only slightly
cool.
Cause:
The expansion valve is stuck open and/or the capillary tube (bulb) is not making proper contact with
the evaporator outlet tube. Liquid refrigerant may
be flooding the evaporator making it impossible for
the refrigerant to vaporize and absorb heat normally. In vehicles where the TXV and sensing bulb
are accessible, check the capillary tube for proper
mounting and contact with the evaporator outlet
tube. Then perform the following test. If the TXV is
not accessible, then proceed to Repair Procedure.
Test:
1. Operate the AC system on it’s coldest setting for
a few minutes. Carefully spray a little nitrogen
or other cold substance, on to the capillary tube
coil (bulb) or head of the valve.
2. The low pressure (suction) side gauge needle
should now drop on the gauge. This indicates the
valve has closed and is not stuck open. Repeat
the test, but first warm the valve diaphragm
with your hand.
Go to Chapter Start - Table of Contents - Index
8-15
Chapter 8 – Troubleshooting & Service Procedures
3. If the low side gauge shows a drop again, the
valve is not stuck. Clean the surfaces of the
evaporator outlet and the capillary coil or bulb.
Make sure the coil or bulb is securely fastened to
the evaporator outlet and covered with insulation material. Operate the system and check performance.
Repair Procedure:
If the test did not result in proper operation of
the expansion valve, the valve is defective and
must be replaced. Recover all refrigerant from
the system and replace the expansion valve and
the receiver-drier. Evacuate and recharge the
system with refrigerant, then check AC operation and performance.
Figure 8-11
System High Pressure Side Restriction
30
LOW SIDE LOW
0
10
20
30
Gauge reading, system high
pressure side restriction.
60
90
120
150
LOW
TEMPERATURE
200
300
0
500
100
400
HIGH SIDE NORMAL-TO-HIGH
HIGH
TEMPERATURE
Tip:
Air from vents in the cab is only slightly cool.
Look for sweat or frost on high side hoses and
tubing, and frost appearing right after the point
of restriction. The hose or line may be cool to the
touch near the restriction.
Cause:
There could be a kink in a line, or other restriction in the high side of the system.
8-16
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Readings
Repair Procedure:
After you locate the defective component containing the restriction, recover all of the refrigerant. Replace the defective component and the
receiver-drier. Evacuate and recharge the system with refrigerant, then check AC operation
and performance.
Compressor Malfunction
Figure 8-12
Gauge reading, compressor
malfunction.
30
LOW SIDE HIGH
0
10
20
30
60
90
120
150
LOW
TEMPERATURE
200
300
0
500
100
400
HIGH SIDE LOW
HIGH
TEMPERATURE
Tip:
The compressor may be noisy when it operates.
Cause:
Defective reed valves or other compressor components. If the compressor is not noisy, there
may be a worn or loose compressor clutch drive
belt.
Repair Procedure:
If you find the belt worn or loose, replace or
tighten it and recheck system performance and
gauge readings. To inspect and service the compressor, you must isolate (front seat the stem
type compressor service valves) and recover refrigerant, or fully recover R-12 from systems
containing Schrader valves. Remove the compressor cylinder head and check the appearance
of the reed valve plate assembly. If defective,
replace the valve plate and install with new gaskets, or replace the compressor assembly.
Go to Chapter Start - Table of Contents - Index
8-17
Chapter 8 – Troubleshooting & Service Procedures
If you find particles of desiccant in the compressor, remove and replace it and the receiver-drier.
Before doing so, back flush other system components (except the expansion valve) using a flushing kit. If there are stem type valves and you
isolate the compressor, the rest of the system
must be purged of refrigerant before you can
disconnect and flush system components (Chapter 9 describes the flushing procedure). After
flushing, reassemble the components. Always
check the oil level in the compressor, even if you
install a new or rebuilt unit. Tighten all connections and evacuate the system. Recharge the air
conditioner with refrigerant and check system
operation and performance.
Note:
Rotary compressors have a limited oil reservoir. Extra oil must be added for all truck
installations
Figure 8-13
Condenser Malfunction or System Overcharge
30
LOW SIDE HIGH
0
10
20
30
60
120
150
LOW
TEMPERATURE
Tip:
8-18
200
90
300
100
400
0
Gauge reading, condenser
malfunction or system
overcharge.
HIGH SIDE HIGH
500
HIGH
TEMPERATURE
The air from vents in the cab may be warm. In R12 systems there can be bubbles in the sight
glass. The high pressure hoses and lines will be
very hot. Don’t forget to check the engine cooling
system components—fan and drive belt, fan
clutch operation, and the radiator shutter.
Go to Chapter Start - Table of Contents - Index
Manifold Gauge Set Readings
Cause:
The condenser is not functioning correctly or
there may be an overcharge of refrigerant inside
the system. Another possibility is lack of (ram)
air flow through the condenser fins during testing. Engine cooling system component malfunction can cause high pressure by blocking air flow
(radiator shutter) or not providing air flow (fan
clutch) in sufficient quantity.
Repair Procedure:
Inspect the condenser for dirt, bugs or other debris and clean if necessary. Be sure the condenser is securely mounted and there is adequate clearance (about 1-1/2 inches) between it
and the radiator. Check the radiator pressure
cap and cooling system, including the fan, fan
clutch, drive belts and radiator shutter assembly. Replace any defective parts and then recheck AC system operation, gauge readings and
performance.
If the problem continues, the system may be
over- charged (have too much refrigerant inside).
Recover the system slowly until low and high
pressure gauges read below normal, and bubbles
appear in the sight glass. Then add refrigerant
(charge the system) until pressures are normal
and the bubbles disappear. Add another quarter
to half pound of refrigerant and recheck AC system operation, gauge readings and performance.
If the high gauge readings do not change, you
should recover all of the refrigerant and flush (it
may be partially plugged) or replace the condenser. Also replace the receiver-drier or accumulator. Then connect the components and
evacuate the system. Recharge the air conditioner with refrigerant and check system operation and performance.
Go to Chapter Start - Table of Contents - Index
8-19
Chapter 8 – Troubleshooting & Service Procedures
Thermostatic Switch Malfunction
30
LOW SIDE NORMAL
0
10
20
30
Gauge reading, thermostatic
switch malfunction.
60
90
120
150
LOW
TEMPERATURE
Tip:
Figure 8-14
200
300
0
500
100
400
HIGH SIDE NORMAL
HIGH
TEMPERATURE
The low side gauge needle may fluctuate in a
very narrow range compared to a normal range.
The compressor clutch may be cycling on and off
more frequently than it should.
The low side gauge needle may fluctuate in an
above normal range as the clutch cycles. This
may be an indication that the thermostat is set
too high (someone may have attempted to adjust
the factory setting). A new thermostat may have
been installed incorrectly (capillary tube not inserted between the evaporator fins in the proper
position).
Cause:
The thermostatic switch is not functioning properly or at all.
Repair Procedure:
Replace the thermostatic switch. When you remove the old thermostat, replace it with one of
the same type. (They operate in a factory preset
temperature range.) Take care in removing and
handling the thermostat and thin capillary tube
attached to it. Don’t kink or break the tube.
Position the new thermostat capillary tube at or
close to the same location and seating depth between the evaporator coil fins as the old one.
Connect the electrical leads.
8-20
Go to Chapter Start - Table of Contents - Index
Review of Frequent Problem Areas
Note:
See the Thermostat section in Chapter 10. Fan
clutch, radiator shutter, condenser, compressor, and the newer air and water valve control
systems are covered in Chapter 10.
Review of Frequent Problem Areas
In HVAC systems a limited number of things can go wrong. Moving parts of the
compressor, clutch, and expansion valve or refrigerant metering device can
malfunction or break down from metal fatigue, contamination, abnormal pressure or lack of lubrication. Electrical connections may corrode, become disconnected or break. Fuses blow from shorts or overload. Belts slip or break.
Vibration from the engine or road surface can work bolts and air or vacuum
lines loose, or rub and break or wear parts out. Motors may burn out. The
inside of the system can become contaminated from moisture, air or desiccant
material breakdown. Refrigerant may leak out of the system quickly or very
slowly. Moisture in the system can combine with refrigerant to form acid and
attack (corrode) metal parts from the inside. Moisture and refrigeration oil can
combine to form sludge that may block refrigerant flow.
The following problems are discussed in more detail in this section:
1. Belts and Compressor Clutch
2. Condenser
3. Refrigerant Lines, Hoses, and Fittings
4. Refrigerant Metering Valves
5. Other Problems
1. Belts and Compressor Clutch
Let’s review problem areas listed at the beginning of Chapter 7. The most
frequent repairs are replacing belts and servicing or replacing the compressor or clutch. Heavy duty vehicle operation puts a lot of stress on
these parts. There are several main reasons.
There is often continuous operation for long periods of time. There may
be frequent sudden RPM variations when shifting gears up or down. For
this reason the AC clutches used in heavy duty systems usually have
double row ball bearings. Vibration and road shock contribute to loose or
broken mounting brackets, electrical connections and fittings. Belts, bearings and compressor reed valves wear out.
Various compressor clutch cutout switches are used because the AC
designers know about compressor operating conditions. System leaks,
high operating pressures, malfunctioning engine cooling system components—all cause compressor problems and failures. When refrigerant and
refrigeration oil leaks out of a system or there is contamination blocking
oil flow, the compressor will be starved for oil and seize.
Go to Chapter Start - Table of Contents - Index
8-21
Chapter 8 – Troubleshooting & Service Procedures
2. Condenser
Condensers get dirty and the dirt reduces heat movement by insulating
the condenser. The fittings come loose or break from stress if the condenser or connecting hoses are not secured properly to keep the effects of
vibration at a minimum.
Heat transfer efficiency and pressure in the condenser are affected by
the amount of outside air flowing through condenser fins. A lack of air flow
can mean the refrigerant doesn’t give up enough heat energy to the
outside air (it doesn’t change state). The refrigerant arrives at the evaporator as a gas and can’t pick up any heat energy from cab air. In the cab,
air from the vents is only slightly cool or warm.
One possible cause of condenser malfunction could be the engine cooling system. This is why fan clutches and radiator shutters are often
controlled or overridden by AC switch function. In fact, we can add fan
clutch, radiator shutters and also fan motors to condenser problems. If
they don’t function to allow sufficient air through the condenser, pressure
inside the system may become dangerously high. A lack of air through the
condenser fins can raise high side pressure and blow out the weakest
point in a system, or damage the compressor.
3. Refrigerant Lines, Hoses and Fittings
Problems with these parts may be caused by normal deterioration, vibration damage, lack of maintenance or human error (improper installation
or replacement). All rubber parts are attacked by ozone (oxygen) in the
air. Rubber parts break down slowly and become more vulnerable to the
effects of vibration with the passage of time.
Heavy duty vehicle vibration causes stress on all lines, fittings and
connections. Regular maintenance includes checking and tightening any
suspect line, or hose retainers, or grommet position where the grommet is
protecting a line or hose from abrasion. Any insulating material wrapped
around hoses must be in place and securely fastened.
4. Refrigerant Metering Valves
When you consider valve problems there are obvious differences in valve
construction and what can go wrong. If a valve is clogged with sludge or
other obstruction, the result is a valve problem but the cause is contamination in the system. Valves get stuck open or closed, although most often
closed when the gas charge is lost from the diaphragm housing in a
traditional TXV. The capillary tube can vibrate loose from the evaporator
outlet tube. The capillary can break and the small quantity of temperature sensitive gas can escape. The diagnosis of a valve as defective calls
for replacement.
5. Other Problems—Leaks, Moisture, and Adding
Refrigerant
Before any refrigerant was put inside the AC system, someone used a
vacuum pump to evacuate any air and moisture. Vacuum is really a force
pulling against all hoses, fittings and components from the inside. When
the system is charged with refrigerant, the pressure goes from minus (a
8-22
Go to Chapter Start - Table of Contents - Index
Conclusion
vacuum) to plus pressure inside the hoses and all components. The
refrigerant and refrigeration oil are trying to escape from the system at
all times.
Technicians frequently add refrigerant to a system, replacing refrigerant seepage through system connections or fittings. If the system has
been maintained regularly (every three to six months), adding a small
amount of refrigerant may result in normal system function. However,
the best procedure is to check all connections and look for, find and repair
any leaks before adding refrigerant.
When your leak detector indicates the presence of a leak, you can’t tell
how long the system has been leaking. Finding one leak doesn’t mean
there are not others. Until you have some AC system work experience, it
will be hard to guess how much refrigerant may have leaked. If you have
to top a system off with a half pound of refrigerant or more, adding
refrigerant is not the answer.
Find the leak. Recover all of the refrigerant and repair the system. The
moisture absorbing capacity of any desiccant material is limited and
cannot be measured. For that reason, replace the receiver-drier or accumulator. Then evacuate the system for an hour and recharge with refrigerant.
When a compressor shaft seal has leaked oil and the refrigerant charge
is a little low, the shaft seal may have leaked because the air conditioner
was not used. The seal can get a little out of round from the weight of the
crankshaft and leak above the shaft. Running the compressor may cause
the seal to swell and close up the leak. The shaft rotation exerts force all
around the seal and puts life back into it. To prevent this from happening,
manufacturers recommend regular AC system operation a minimum of
every couple of weeks even in cool weather.
Keep in mind that the compressor can cause a vacuum inside the system if
there is a restriction in the system. That means it can suck air and
moisture inside under some conditions. It will pull these contaminants in
through the same space where refrigerant and refrigerant oil has leaked
out.
Conclusion
What could the air conditioning problem and it’s cause have been at the
beginning of this chapter? The operator was in a hurry, but you were able to
start your troubleshooting with the answers he gave you. Problems your
inspection may have turned up are a very low refrigerant charge, a contaminated system or defective compressor. Those are not quick fix jobs.
On the other hand, you might have found enough debris on the condenser fin
surface to boost high side pressures to an abnormal level during the hottest
part of the day. So the Trinary™ or high pressure switch would cut out from
high pressure—but reset itself. You cleaned the condenser, added a half pound
of refrigerant and AC system pressures and function returned to normal.
Service and repair took a half hour. But there was no way to tell without using
your knowledge and experience. By now you are pretty familiar with AC
system problems, the reasons for some of them, troubleshooting and repair. In
Chapter 9 we will describe complete system purging, evacuation, flushing and
recharging.
Go to Chapter Start - Table of Contents - Index
8-23
• Description and Properties of Refrigerants
• Changes in Service Procedures
• Recovering and Recycling the Refrigerant
• Flushing the AC System
• Evacuating and Charging the AC System
• Reclaiming a Refrigerant
• Chapter Review
Description and Properties of Refrigerants
Refrigerants are contained in the closed system of an air conditioner and
circulate under pressure, moving heat energy from the cab to the outside air.
Different refrigerants require different operating pressures, causing the refrigerant to undergo a “change of state” (refer to Chapter 1 — HVAC Function).
Changes in Service Procedures
RE
R
Since the beginning of 1992, the EPA has required that any refrigerant removed from an AC system be recovered and recycled before reuse. Unlike the
purging process which releases ozone depleting refrigerant into the atmosphere, the recovery processes allow us to use the same refrigerant over and
over.
CY
VE
Click on any of these
subject headings to go
directly to the page
CL
CO
9
E
RE
Chapter
Refrigerants
RECLAIM
A major difference between purge and recovery/recycle procedures is the refrigerant is contained in an externally sealed container when undergoing recovery/
recycle procedures in order to ensure environmentally safe processing.
In order to reuse a refrigerant in an AC system, the following steps are
required:
1.
2.
3.
4.
5.
6.
7.
Prepare the station for the recovery process
Recover refrigerant from the AC system
Recycle the recovered refrigerant
Perform the maintenance or repair the system
Flush the AC system when necessary
Evacuate the AC system
Charge the AC system with recycled refrigerant
Go to Table of Contents - Index
9-1
Chapter 9 - Refrigerants
Recycling the refrigerant involves the following processes:
• Recovery — You recover a refrigerant when you remove it from
an AC system (in order to repair or replace a component) and then
store, transport, recycle, or reclaim it. This is a closed loop process. The recovered refrigerant may vary in quality. Refer to the
Recovering and Recycling the Refrigerant section for a complete
description of the recovery process.
• Recycle — You recycle a refrigerant when you remove contaminants such as moisture, acidity, and particulate matter. Many
refrigerants are reusable at this stage. Refer to the Recovering
and Recycling the Refrigerant section for a complete description of
the recycle process.
• Reclaim — You reclaim a refrigerant when you send it to an
outside facility which can restore it to a new product specification.
This reprocessing usually includes both a chemical analysis and
distillation of the recycled refrigerant. Refer to the Reclaiming the
Refrigerant section for a complete description of the recycle process.
Recharging an AC system requires the following procedures:
• Flush — You flush certain AC system components and hoses to
remove contaminants within them. Flushing prepares the AC
system for the new refrigerant. Refer to Flushing the AC System
section below.
• Evacuate — You evacuate the AC system to remove moisture and
air. Refer to the Evacuating and Charging the AC System section
below.
• Charge — You charge the AC system by adding new refrigerant
to the system.
Recovering and Recycling the Refrigerant
Recovery/Recycle Station
When troubleshooting indicates that a component in a closed AC system
be replaced or removed for service, refrigerant must be removed from the
system. A handy, dual purpose station performs both recovery and recycle
procedures allowing us to follow the new guidelines for handling used
refrigerant. The recovered refrigerant can then be recycled to reduce
contaminants, and reused.
Equipment is also available to just remove or extract the refrigerant.
Extraction equipment does not clean the refrigerant. It is used to recover
the refrigerant from an AC system prior to servicing.
To accomplish this, the recovery/recycle station separates the oil from
the refrigerant and filters the refrigerant multiple times to reduce moisture, acidity, and particulate matter found in a used refrigerant.
CAUTION
9-2
Mixing refrigerant types damages equipment. Dedicate one recovery/recycle station to each type of refrigerant processing to avoid equipment damage.
Go to Chapter Start - Table of Contents - Index
Recovering and Recycling the Refrigerant
Figure 9-1 shows a recovery/recycle machine. Recycle equipment must
meet certain standards as published by the Society of Automotive Engineers and carry a UL approved label. The basic principals of operation
remain the same for all machines, even if the details of operation differ
somewhat.
Figure 9-1
Recycle station.
A full system recovery is not necessary when you service or replace a
compressor with stem type service valves. These valves may be front
seated to isolate the rest of the AC system from the compressor. The
refrigerant stays in the system and only the refrigerant in the compressor
is recovered, recycled and replaced.
Note:
Keep the collection cylinder in an upright position for
the duration of the recovery/recycle cycle to ensure no
liquid is drawn back into the system.
Draining the Oil from the Previous Recovery Cycle
In preparation for recovery, do the following:
1. Place the power switch and the controller on the recovery unit
in the OFF position.
2. Plug in the recovery station to the correct power source.
3. Drain the recovered oil through valve marked OIL DRAIN on
the front of the machine.
4. Place the controller knob in the ON position. The low pressure
gauge will show a rise.
5. Immediately switch to the OFF position and allow the pressure to stabilize. If the pressure does not rise to between 5
psig and 10 psig, switch the controller ON and OFF again.
With practice, this procedure should become easier.
Go to Chapter Start - Table of Contents - Index
9-3
Chapter 9 - Refrigerants
6. When the pressure reaches 5 to 10 psig, open the OIL DRAIN
valve, collect oil in an appropriate container, and dispose of
container as indicated by local, state, or Federal Regulation.
THE OIL IS NOT REUSABLE, DUE TO CONTAMINANTS
ABSORBED DURING ITS PREVIOUS USE.
Performing the Recovery Cycle
You are now ready to recover. Follow these steps:
1. Be sure the equipment you are using is designated for the
refrigerant you intend to recover.
2. Record the sight glass oil level. Having drained it, it should be
zero.
3. Check the cylinder refrigerant level before beginning recovery
to make sure you have enough capacity.
4. Confirm that all shut-off valves are closed before connecting
to the AC system.
5. Attach the appropriate hoses to the system being recovered.
6. Start the recovery process by operating the equipment as per
the manufacturer’s instructions.
7. Continue extraction until a vacuum exists in the AC system.
8. If an abnormal amount of time elapses after the system
reaches 0 psig and does not drop steadily into the vacuum
range, close the manifold valves and check the system pressure. If it rises to 0 psig and stops, there is a major leak. Refer
to Chapter 8 for troubleshooting leak procedures.
9. Check the system pressure after the recovery equipment
stops. After five minutes, system pressure should not rise
above “0” gauge pressure. If the pressure continues to rise,
restart and begin the recovery sequence again. This cycle
should continue until the system is void of refrigerant.
10. Check the sight glass oil level to determine the amount of oil
that needs to be replaced.
11. Mark the cylinder with a RECOVERED (red) magnetic label
to reduce the chance of charging a system with contaminated
refrigerant. Keep a record of the amount of refrigerant recovered, if you have the capability.
WARNING
Check the sight glass oil level to determine the
amount lost during recovery. You must add this
amount of oil back into the system.
Performing the Recycling Procedure
The recovered refrigerant contained in the cylinder must undergo the
recycle procedure before it can be reused. The recycle or clean mode is a
continuous loop design and cleans the refrigerant rapidly. Follow equipment manufacturer’s instructions for this procedure.
9-4
Go to Chapter Start - Table of Contents - Index
Recovering and Recycling the Refrigerant
Purging Non-Condensable Gases (Air)
During purging and refrigerant recovery air can be entrapped in the
refrigerant container. Air must not be put into an AC system. The result is
higher operating pressures and possible system damage.
A simple check can be performed as follows:
1. Store the recovered refrigerant at constant temperatures
above 65° F (18.7° C). The container should include a pressure
gauge reading to 1 psi increments. The container should not
be in direct sunlight or near a heat source.
2. Use a calibrated thermometer to establish temperature
within 4 inches of the container.
3. Compare the pressures for like temperatures in Figure 9-2.
Note the separate charts for R-12 and R-134a. If the container
pressure is equal to or less than the pressure shown in the
table, excess air is not present.
4. If container pressure is greater than shown in the table,
connect the container to recovery or recycle equipment with
the pressure gauge in place.
5. Bleed a small amount of vapor from the container until the
pressure is below that shown on the table, then close the
valve.
6. Tank temperature may change during the bleed off process.
Mild shaking will assist in temperature stabilizing, but it is a
good idea to let it set for several hours before again checking
pressure against the table.
7. If the pressure remains above that shown on the table, excess
air or another contaminant (i.e., another refrigerant) is still
present. This material must be recycled or reclaimed.
8. If the pressure is equal or below that shown on the table
identify the cylinder as “recycled.”
Go to Chapter Start - Table of Contents - Index
9-5
Chapter 9 - Refrigerants
Figure 9-2
R-12 Allowable Container Pressure
°F
Psig
°F
Psig
°F
Psig
°F
Psig
°F
Psig
65
66
67
74
75
76
75
76
77
87
88
90
85
86
87
102
103
105
95
96
97
118
120
122
105
106
107
136
138
140
68
69
70
78
79
80
78
79
80
92
94
96
88
89
90
107
108
110
98
99
100
124
125
127
108
109
110
142
144
146
71
72
73
74
82
83
84
86
81
82
83
84
98
99
100
101
91
92
93
94
111
113
115
116
101
102
103
104
129
130
132
134
111
112
113
114
148
150
152
154
°C
kPa
°C
kPa
°C
kPa
°C
kPa
°C
kPa
18.3
18.9
19.4
510
517
524
23.9
24.4
25.0
600
607
620
29.4
30.0
30.6
703
710
724
35.0
35.6
36.1
814
827
841
40.6
41.1
41.7
938
952
965
20.0
20.6
21.1
538
545
552
25.6
26.1
26.7
634
648
662
31.1
31.7
32.2
738
745
758
36.7
37.2
37.8
855
862
876
42.2
42.8
43.3
979
993
1007
21.7
22.2
22.8
23.3
565
572
579
593
27.2
27.8
28.3
28.9
676
683
690
696
32.8
33.3
33.9
34.4
765
779
793
800
38.3
38.9
39.4
40.0
889
896
910
924
43.9
44.4
45.0
45.6
1020
1034
1048
1062
The pressures in these
English and metric charts
refer to recycled R-12 and R134a refrigerant, respectively.
R-134a Allowable Container Pressure
°F
Psig
°F
Psig
°F
Psig
°F
Psig
°F
Psig
65
66
67
69
70
71
76
77
78
85
86
88
87
88
89
103
105
107
98
99
100
125
127
129
109
110
111
149
151
153
68
69
70
73
74
76
79
80
81
90
91
93
90
91
92
109
111
113
101
102
103
131
133
135
112
113
114
156
158
160
71
72
73
77
79
80
82
83
84
95
96
98
93
94
95
115
117
118
104
105
106
137
139
142
74
75
82
83
85
86
100
102
96
97
120
122
107
108
144
146
115
116
117
118
119
120
163
165
168
171
173
176
°C
kPa
°C
kPa
°C
kPa
°C
kPa
°C
kPa
18
19
20
476
483
503
25
26
27
593
621
642
32
33
34
752
765
793
39
40
41
917
945
979
46
47
48
1124
1158
1179
21
22
23
524
545
552
28
29
30
655
676
703
35
36
37
814
841
876
42
43
44
1007
1027
1055
49
1214
24
572
31
724
38
889
45
1089
Flushing the AC System
Flushing has long been recommended as a means of removing contaminants or
other debris from certain system components. The normal flushing materials,
such as R-11, are now prohibited.
Using compressed air is not a good method of flushing. Air should never be
used in an R-134a system. Closed loop flushing kits are now available, although they may not remove all foreign material.
9-6
Go to Chapter Start - Table of Contents - Index
Evacuating and Charging the AC System
The primary use of a flushing kit is to remove contaminants from the AC
system hoses, evaporator, and condenser. Any other component of an AC
system should be bench checked or replaced, since flushing may be ineffective
or may damage a component. Flushing is usually performed after the recovery
process. We recommend it before you replace the compressor, or when you find
contamination in other components (receiver-drier, expansion valve, or connections). Some recover/recycle machines have optional “flush kits.” The only
proper way to flush system components is to use refrigerant in a closed-loop
system.
Evacuating and Charging the AC System
Evacuate the system once the air conditioner components are repaired or
replacement parts are secured, and the AC system is reassembled. Evacuation
removes air and moisture from the system. Then, the AC system is ready for
the charging process, which adds new refrigerant to the system.
Evacuating the System
Follow this procedure:
1. Tighten all connections and attach a vacuum pump to the
center hose of the gauge set.
MANIFOLD GAUGE SET
Figure 9-3
GAUGE READINGS
This illustration shows
evacuation of an AC system
before recharging. It is very
important to run the
vacuum pump long enough
to insure the removal of any
moisture that may be in the
system.
LOW SIDE
READS IN
VACUUM
30
0
10
20
30
HIGH SIDE
READS BELOW
ZERO (0)
60
90
200
300
0
500
100
120
150
LOW
TEMPERATURE
400
HIGH
TEMPERATURE
HAND
VALVE
OPEN
HAND
VALVE
OPEN
GAUGE CENTER HOSE
TO VACUUM PUMP
FROM LOW SIDE
COMPRESSOR
SERVICE VALVE
TO
VACUUM
PUMP
FROM HIGH SIDE
COMPRESSOR
SERVICE VALVE
2. Start the vacuum pump and open both the hand valves on the
manifold all the way. Run the pump for five minutes, then
close the hand valves and shut off the pump.
3. Check the gauge readings for five minutes. If the gauge
needles move up, the system is not sealed. There is a leak. Air
and moisture are being sucked into the system by the
vacuum.
4. Tighten any loose connections. Re-start the pump, and open
the hand valves on the gauges again. Repeat the vacuum test.
Go to Chapter Start - Table of Contents - Index
9-7
Chapter 9 - Refrigerants
5. Run the vacuum pump for at least an hour to remove the
moisture from the system.
The moisture must turn to gas before the pump can pull it out. The
moisture takes time to boil away, so that it can be drawn out of the system.
Your vacuum pump can draw most of the air out pretty quickly. But a
deep vacuum requires more time; the deeper the vacuum the longer it
takes to get there. To ensure the least possible amount of air and moisture
in the system, buy a good quality vacuum pump, take care of it, and use it
for at least an hour.
Figure 9-4
Vacuum pump.
WARNING
Lubricants removed during the recovery process must
be replaced with new lubricants.
Charging the AC system
*Use a charging station whenever possible.
When adding a full charge of refrigerant, you can put it in as a gas or as
a liquid. Adding refrigerant as a liquid is faster but can damage the
compressor if not done correctly. The procedure you use, and where you
add the refrigerant in the AC system makes a difference. When using
refrigerant as a liquid, never add more than two thirds of system requirements as a liquid. Finish charging the system using gas. Always keep the
refrigerant containers in an upright position so that no liquid is drawn
into the system.
Refer to the Charging with Refrigerant Gas section below for the
procedure for gas charging. Refer to the Charging the System with Liquid
Refrigerant section for the procedure for liquid charging.
Charging with Refrigerant Gas (on the Low Side)
Perform this procedure to charge with refrigerant gas:
1. Use a charging meter or station to select the exact amount of
refrigerant required. Never add more than the amount of
refrigerant recommended by the manufacturer (in pounds
and ounces). To measure, use a container and scale, or charging station.
9-8
Go to Chapter Start - Table of Contents - Index
Evacuating and Charging the AC System
2. Connect the center service hose from the gauge set to the
refrigerant container dispensing valve. Purge the hose of any
air using refrigerant gas pressure from the container.
3. Run the engine at 1200 to 1500 RPM, with the AC unit on
maximum cool.
4. Open the dispensing valve, then the low side hand valve on
the manifold. Figure 9-5 illustrates system charging with
refrigerant gas entering the compressor on the suction (low
pressure) side of the system.
Note:
If there are no manufacturer’s charging specifications, you can watch the sight glass first for bubbles,
then clearing.
LOW SIDE
GAUGE
Figure 9-5
In this illustration, refrigerant is added on the low side
of the system as a gas. The
engine must be running at
1200 to 1500 RPM to draw
the gas in.
30
0
10
20
30
60
90
120
150
LOW
TEMPERATURE
CHARGING HOSE
HIGH SIDE
GAUGE
200
300
0
500
100
400
HIGH
TEMPERATURE
LOW SIDE:
KEEP HAND
VALVES OPEN
HIGH SIDE:
HAND
VALVES CLOSED
SUCTION HOSE
LOW SIDE
SERVICE VALVE
HIGH SIDE
SERVICE VALVE
DISPENSING
VALVE
REFRIGERANT TANK
5. Check the sight glass when you have added nearly the specified amount of refrigerant. Keep adding refrigerant until the
sight glass clears or you have added the specified refrigerant
charge. Use an oil injector to replace oil drained from the
system. Remember, a large leak may have resulted in nearly
all the lubricant being lost.
6. Close the valve on the refrigerant container. Close the hand
valve on the gauge set and check the gauge readings. The
gauges should read in the normal range.
7. Turn off the engine and AC system. Check for leaks. If the
system checks out OK, back seat the service valves. Remove
the manifold gauge set hose fittings from the compressor. If
Schrader valves are in use, be sure to remove the manifold
hose fittings quickly and carefully, using a glove or shop towel
to protect your hand. Replace the protective caps on the
compressor service valves.
Go to Chapter Start - Table of Contents - Index
9-9
Chapter 9 - Refrigerants
Charging the System with Liquid Refrigerant
This process is used as a time-saver, but requires much more care to avoid
compressor damage.
1. Check the amount of refrigerant recovered, and add approximately two thirds of that amount, and no more than recommended by the manufacturer (in pounds and ounces).
2. Connect the center service hose from the gauge set to the
refrigerant container dispensing valve.
3. Add refrigerant liquid through the compressor discharge service valve (high side of system). If an accumulator is used, add
the liquid refrigerant (and gas during final charging) via a
Schrader valve.
4. Open the refrigerant dispensing valves and hand valves on
the hose and gauge set. Liquid refrigerant flows into the
system.
Figure 9-6 illustrates how to connect the manifold gauge set
when adding liquid at the compressor (or accumulator).
Figure 9-6
30
60
0
10
20
30
120
150
LOW
TEMPERATURE
REFRIGERANT TANK
INVERTED
LOW SIDE HAND
VALVES CLOSED
200
90
Adding refrigerant liquid to
partially charge the AC
system is illustrated and
described.
300
100
400
0
500
HIGH
TEMPERATURE
HIGH SIDE HAND
VALVES OPEN
HIGH SIDE HOSE
SUCTION HOSE
LOW SIDE
SERVICE VALVE
HIGH SIDE
SERVICE VALVE
CHARGING HOSE
DISPENSING VALVE
5. When you have added two thirds of the recorded, actual
recovered amount of refrigerant, shut off the refrigerant supply. If you added liquid refrigerant at the compressor high side
service fitting, there may be liquid in the compressor. Attach a
wrench to the nut holding the clutch the compressor shaft.
Turn the compressor shaft a few times in the direction of
normal rotation to clear any liquid from the compressor.
6. Finish charging the system with refrigerant gas by starting
the engine and AC system. Follow the procedure for charging
with gas as shown in Figure 9-5.
9-10
Go to Chapter Start - Table of Contents - Index
Chapter Review
Reclaiming Refrigerant
Reclaiming refrigerant reprocesses the material to virgin purity. For sources of
reclaimed refrigerant or to send refrigerant for reclamation, contact the EPA,
the independent industry organizations, or your state’s Department of Ecology.
Chapter Review
• Common refrigerants have varying properties and operating
pressures.
• New laws require that we standardize our refrigerant processing
methods throughout the industry. This includes the processes
that handle refrigerant, including recovering and recycling,
which are the most economic and environmentally friendly ways
of handling the refrigerant.
• Recovery/recycle processes deal directly with the refrigerant.
During recovery the refrigerant is removed from the AC system.
During recycling it is restored to reusable condition by removing
moisture, acidity, and particulate matter.
• The flushing procedure removes contaminants from the AC system hoses, evaporator, and condenser. The evacuation process
removes air and moisture from the AC system. This is necessary
before adding new or recycled refrigerant. The process of adding
refrigerant is called charging.
• Reclaiming a refrigerant means processing the refrigerant so
that it meets standards for new refrigerant.
Go to Chapter Start - Table of Contents - Index
9-11
10
Chapter
Click on any of these
subject headings to go
directly to the page
Component Repair or
Replacement
• Tips on Component Repair or Replacement
• Servicing the Compressor
• HVAC Control System Variations—Troubleshooting
• Servicing and Repairing the Heater
• Summary
Tips on Replacing & Repairing AC Components
The following service and repair procedures are not any different than typical
vehicle service work. However, AC system parts are made of soft metals
(copper, aluminum, brass, etc.). The comments and tips that follow will make
your job easier.
CAUTION
Note:
All of the service procedures described are only performed after the AC system refrigerant has been recovered. Never use regular shop oil or joint compound
to lubricate or seal any AC connections.
To help prevent air, moisture or debris from entering
an open system, cap or plug open lines, fittings or
components as soon as they are disconnected. Keep
all connections (also the caps or plugs you might use)
clean so no debris can accidentally get inside the
system.
As a general rule in AC service, replace any gaskets and O-rings with new ones.
Use fresh refrigeration oil to lubricate connections, gaskets and O-rings. The
following parts are discussed further in this section:
1. Hoses and Fittings
2. Lines
3. Expansion Valves
4. Expansion Tubes
5. Receiver-Drier and Accumulator
6. Compressor & Clutch
1. Hoses and Fittings
When replacing hoses be sure to use the same type and ID hose you
removed. When hoses or fittings are shielded or clamped to prevent
vibration damage, be sure these are in position or secured. On R-134a
systems make sure replacement hose has been designed for this refrigerant.
Go to Table of Contents - Index
10-1
Chapter 10 – Component Repair or Replacement
Machine crimped fittings are preferred over those fittings which use hose
clamps. Properly crimped ferrules make stronger connections than hose
clamps, and are recommended by the manufacturers of refrigerant hose.
Use crimped fittings on hose brands such as Goodyear Galaxy. Steel
fittings are preferred over aluminum in heavy duty applications. Use
reusable fittings on the nylon-lined hose brands such as Aeroquip FC 202.
2. Lines
Always use two wrenches when disconnecting or connecting AC fittings
attached to metal lines. You could be working with copper and aluminum
tubing which can kink or break easily. Tube O-ring type fittings require
only 18 foot pounds of torque for correct sealing. When there are grommets or clamps used to prevent line vibration, be sure these are in place
and secured.
3. Expansion Valves
When removing the expansion valve from the system, remove the insulation, clean the area, and disconnect the line from the receiver-drier.
Detach the capillary (bulb) and external equalizer tube (if present) from
their mounting locations. Remove the expansion valve from the evaporator inlet. Expansion valve service is limited to cleaning or replacing the
filter screen. If this is not the problem, replace the valve. If there is any
debris in a block-type valve, replace it. Secure the capillary and equalizer,
if used, and replace any insulating material.
4. Expansion Tubes
A clogged or defective expansion tube must be replaced. There are special
tools available to remove and replace tubes at their location. If you don’t
have one, you may be able to use a pair of needle-nose pliers. Put a little
refrigerant oil in the evaporator inlet to lubricate the expansion tube for
easier removal. Discard the old tube. Lubricate the new tube and O-ring
and insert until it seats against the dimples in the evaporator inlet.
5. Receiver-Drier & Accumulator
The receiver-drier and accumulator can not be serviced or repaired. They
should be replaced whenever the AC system is opened for any service. If
the receiver-drier or accumulator has a pressure switch to control the
clutch, it should be removed and installed on the new unit.
6. Compressor & Clutch
Problems with the clutch assembly can be due to low voltage, electrical
failure in the coil, the lead wire or a bad pulley bearing. Check first to see
that electrical power is reaching the clutch. The lead wire and bearing can
be replaced and the clutch assembly reinstalled. If the coil fails, it must be
replaced. If the clutch shows obvious signs of excessive heat, replace the
complete assembly. The compressor can fail due to shaft seal leaks,
defective valve plates, bad bearings, or problems associated with high
pressure, heat or lack of lubrication.
10-2
Go to Chapter Start - Table of Contents - Index
Replacing & Repairing AC Components
Figure 10-1
POWER IN (12V DC)
Wiring schematic for the
clutch circuit. Two or more
of these switches may be
found in a clutch circuit.
CIRCUIT BREAKER OR FUSE
CONTROL SWITCH (HEAT/AC SWITCH
OR INCLUDED IN FAN SPEED SWITCH)
PRESSURE SWITCH (NEAR CONTROL
PANEL ON AIR CONTROL SYSTEM)
THERMOSTAT SWITCH
TRINARY™ OR BINARY™ SWITCH
LOW SIDE LOW PRESSURE SWITCH (LSLP)
POWER IN
HIGH SIDE LOW PRESSURE SWITCH (HSLP)
CIRCUIT BREAKER
OR FUSE
HIGH SIDE HIGH PRESSURE SWITCH (HSHP)
RELAY (OPTIONAL)
CLUTCH COIL
Servicing the Compressor
Every AC system and compressor depends on refrigeration oil for lubrication
and safe operation. Whenever an AC system is opened for service, check the
compressor oil level and add clean refrigeration oil as required by manufacturer specs. This is especially important with a rotary compressor that has no
oil sump.
WARNING
Different lubricants are used in R-12 and R-134a systems. They must not be mixed.
Compressor Repair
Vehicle down time or travel delay can be very costly to the heavy duty rig
operator. For this reason, compressor service and repair is usually more
costly than replacement with a new or rebuilt compressor. We have
limited compressor and clutch service and repair coverage because each
compressor make (and model) requires special tools and procedures for
complete repair capability. Compressor manufacturers publish service
manuals for their products.
HVAC Control System Variations—Troubleshooting
We described Binary™ and Trinary™ switches, air operated controls (Air
Block) and CTC™ or Constant Temperature Control in Chapter 5. These
control devices are often specified on heavy duty vehicle HVAC systems.
Troubleshooting and servicing are explained here.
Go to Chapter Start - Table of Contents - Index
10-3
Chapter 10 – Component Repair or Replacement
Troubleshooting for the following components is discussed below:
1. Binary™ and Trinary™ Switches
2. Air Operated Controls
3. CTC™ System
1. Binary™ and Trinary™ Switch—Troubleshooting
The high/low pressure function of the Binary™ and Trinary™ switches
acts as a circuit breaker for the AC system. The switch interrupts current
flow to the clutch when there is abnormal pressure in the system. A
combination of components or wiring problems could cause the system to
malfunction. In many cases, problems associated with these switches are
the result of a malfunction elsewhere in the system.
Note:
Terminal numbers are molded into the top of the
Trinary™ switch. Terminals 1 and 2 control the compressor clutch and are identical to the two terminals
on the Binary™ switch.
AC Compressor Clutch Circuit
In normal operation, the Binary™ and Trinary™ terminals, #1 and
#2, should form a closed circuit. They supply power to the clutch if
the AC system is properly charged with refrigerant, and the outside
air temperature is above 40 degrees Fahrenheit.
AC Clutch Does Not Engage.
1. With the system on, check power at Trinary™ switch with
voltmeter or trouble light:
a. One of the terminals, #1 or #2, should have power.
b. If there is no power, there is a problem with the AC unit
or wiring.
2. Both terminals have power:
a. The problem is either the clutch or the wiring from the
switch to the clutch.
3. Power to and from the Binary™ or Trinary™ check out OK:
a. Use the manifold gauge set to check out system pressures. (Outside temperature must be above 40° F).
b. If system pressure is below 40 PSIG, check for refrigerant leaks. If OK, add refrigerant to obtain correct pressure.
4. AC system pressure and power supply to switch check out
OK:
a. Connect a temporary jumper wire between terminals #1
and #2.
b. The clutch should engage. Operate the AC system for five
minutes at maximum cooling. Disconnect jumper wire
and reconnect the switch leads. If the clutch will not
engage, and pressure is over 50 PSIG, replace the switch.
10-4
Go to Chapter Start - Table of Contents - Index
HVAC Control System Variations
CAUTION
Do not operate AC system with incorrect refrigerant
charge or compressor damage may occur.
Compressor Cycles, but AC System Does Not Cool.
All electrical components in the clutch circuit appear to be functioning properly. Refer to Chapter 8 for troubleshooting procedures.
Power to Trinary™ OK and Compressor Still Runs
Continuously.
The high side cutout switch may not be functioning, so one of the
problems described below is causing the abnormal pressures.
1. Check high side pressure. If it approaches 300 PSIG, a
serious problem is indicated.
a. The AC system may be overcharged.
b. There may not be enough air flow through the condenser
or it may be blocked by debris.
c. The condenser may be too small for operating conditions.
d. There may be a restriction inside the system (bent or
kinked lines or hoses, sludge or moisture in system, etc.).
e. The thermostat may not be functioning.
Fan Clutch or Shutter Override Circuit.
Note:
In normal operation, Trinary™ switch terminals #3
and #4 are normally open. (Normally closed Trinary™
switches are used with some air-clutching engine
fans.) As the system pressure reaches mid-range
(200-230 PSIG), the switch closes and supplies power
to the fan clutch or shutter control circuits.
Fan Clutch or Shutter Cycles Too Often or Stays On Too Long:
1. Connect gauge set to AC system:
a. Watch high pressure side increase until mid-range pressure is reached.
b. If fan engages or shutter opens at the proper pressure,
the Trinary™ is OK.
c. The problem is the condenser—check for debris or lack of
air flow through the condenser fins. The condenser may
be too small for conditions.
2. Fan or shutter cycles at less than 180 PSIG or remains on
below 150 PSIG:
a. The Trinary™ is functioning below it’s proper operating
range and must be replaced.
Go to Chapter Start - Table of Contents - Index
10-5
Chapter 10 – Component Repair or Replacement
Fan Clutch Will Not Activate.
1. Check power supply to terminals #3 and #4 with voltmeter
or trouble light. System pressure must be above 230 PSIG
(restrict air flow through the condenser if necessary to
achieve this pressure). Check opposite terminals for switch
function. If switch does not close and activate the fan
clutch, replace the Trinary™.
Note:
Some air-clutching engine-fan systems use normally
closed Trinary™ switches (Bendix, Horton, etc.).
When the operating pressure is reached, the fan circuit will open and the fan will come on.
2. Faulty solenoid (air-clutching fans) or wiring. If the Trinary™ switch functions in the above test, check wiring to
solenoid valve, fan, or relay, and determine if the valve or
relay is functioning properly.
Air Operated Controls
Air controls have become important in truck HVAC system operation. In
discussing troubleshooting, we will cover the module air control system.
The four major components of this system are illustrated in Figure 10-2
and described as follows:
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SS
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CONTROL LEVER
WITH DEPRESSIONS
The AIR BLOCK is shown
and described in this illustration.
PINTLE ASSEMBLY
CLOSED
AIR
AIR BLOCK CLOSED
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,,
QQ
R
SS
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Figure 10-2
OPEN
O-RINGS
AIR
AIR BLOCK OPEN
Air Block—A molded plastic or machined metal block with air
passageways; inlet, outlet and vent ports.
Pintle—A valve stem with head and O-ring seal
10-6
Go to Chapter Start - Table of Contents - Index
HVAC Control System Variations
Control Lever—A sliding flat metal plate with formed depressions
(or cavities) programmed to position the pintles for each mode of
HVAC system operation.
Air Cylinder—A single or double action spring return device to
position air directional control doors.
Air controls are assembled so the pintles are retained in the passageways of the air block by a mode selector lever. Air control functions
(modes) are programmed by the depressions (or cavities) formed in
the control lever. As the control lever is moved to an operator selected mode, the pintles slide in and out of the depressions. This
action moves the pintles and their O-rings in the air passageways of
the air block, allowing air to flow or vent from the air cylinders.
Doors located in the AC unit or duct system will open or close as the
air cylinders are activated, directing heated or cooled air to the
desired outlets.
If the air control panel shows signs of internal leaking, it should
be replaced using an air service kit. An air service kit includes the
assembled block, pintles and control levers. Do not attempt to replace individual components of the air control panel.
Before replacing any air control system parts look for air leaks in
the system.
Air Leaks in System.
Check for loose air fitting connections on the air block and air
cylinders. Examine the air hose. NOTE: To remove hose from Legris
air fittings, push on the metal ring or color coded button around the
hose, and pull hose from fitting.
1. Check for leaks around fitting seals:
a. Hose must be cleanly cut at a 90° angle to seal in fitting.
b. Hose must be pushed all the way into the fitting (about
9/16").
c. Cleaning hose and applying a thin coat of light weight oil
will help seal hose in fitting.
2. Inspect hose for cracks:
a. Check the air block assembly. If there is a leak around
pintles, replace assembly. Do not try to disassemble and
repair.
b. Check air cylinders for leaks.
Modes do not Function as Control Lever is Moved.
Check air supply to the control panel. Check for sticking doors
(defrost, vent, etc.), and jammed air cylinders. Inspect air block
assembly.
1. Cycle the control lever and listen for air escaping from
exhaust port (vent). The air cylinders will not retract unless
the air block vents properly. Replace block if it does not vent.
2. Disconnect air lines going to cylinders. Cycle control lever.
Listen for air exiting the ports. If there is no air in at least
one lever position, replace assembly.
Go to Chapter Start - Table of Contents - Index
10-7
Chapter 10 – Component Repair or Replacement
Problem Activating AC Clutch Circuit.
Inspect the low pressure switch located on the air block. The switch
is normally closed. It must have air pressure to disengage the clutch.
If there is no power to the clutch proceed as follows.
1. Make sure there is power to the pressure switch—use a
voltmeter or trouble light to check.
2. Make sure there is air to the controls.
3. If there is air and power available, place a jumper across the
two terminals on the low pressure switch. If the clutch engages, there is a problem with the pressure switch or air block.
4. Remove the switch from the air block, move the lever to heat
mode. If air exhausts from the port, replace the pressure switch.
If no air is vented from the port, the air block is defective.
5. If the air block and pressure switch check out OK, inspect
AC system clutch, thermostat, Trinary™ switch, or other
pressure switches, and wiring.
CTC™ (Heater) and CTC™ II (Heater–A/C System)
The constant temperature control systems maintain a pre-selected cab
temperature by pulsating the flow of hot engine coolant through the
heater core. In the CTC II configuration the compressor is cylced to
control temperature in the AC mode. The four major components of the
system are illustrated in Figure 10-3 and described as follows:
THERMOSTAT
CONTROL PANEL
VARIABLE RESISTOR
COOL
HEAT
COMPRESSOR
TRUCK
AIR IN
E/C TO
CONTROL PANEL
SOLENOID
AIR
AIR TO
CONTROL PANEL
EVAPORATOR
DEFROST
Figure 10-3
E/C
CONDENSER
RECEIVER-DRIER
The CTC II system is shown
in this drawing.
FREON
AIR
TEMPERATURE
SENSOR
AIR OPERATED
WATER VALVE
HOT WATER IN
AC MODE
PRESSURE
SWITCH
HEATER CORE
ELECTRONIC
CONTROL
MODULE
TREATED
AIR
EXPANSION
VALVE
TO ACTIVATOR
Circuit Board Assembly—The assembly is located on the heater/AC
unit. It supplies power to resistor and solenoid, and monitors air output
temperature.
Variable Resistor—Located on the control panel and used with temperature control lever to select desired temperature. It translates the
desired temperature into a control voltage for the circuit board.
10-8
Go to Chapter Start - Table of Contents - Index
HVAC Control System Variations
Solenoid Valve—Located on the HVAC unit or near the water valve.
It receives power from the circuit board and controls the air supply to the
water valve.
Air operated Water Valve—The preferred location is on the engine
side of the firewall. Air pressure to the water valve is controlled by the
opening and closing of the solenoid valve. When the solenoid valve is open,
air pressure closes the water valve. The water valve is located on the inlet
side of the heater core.
You will need Constant Temperature Control analyzers to troubleshoot
the CTC™ systems. The vehicle must be operating at proper engine
coolant temperature, air pressure and voltage output in order to troubleshoot the two possible failure modes.
Servicing and Repairing the Heater
Heater service and repair may be necessary because of lack of maintenance.
The rubber parts: belts, heater and radiator hoses all fail in time. Engine
coolant should be replaced every year and the whole system should be flushed
when this is done. The thermostat and radiator pressure cap may fail from
metal fatigue.
Heater valves (water and air), the core, or control devices may malfunction
and require adjustment or replacement. In addition to your normal tool chest
items, the cooling system test equipment required is described in Chapter 6.
Summary
By now you should have a pretty good idea about what is involved in HVAC
function, service and repair. With a sound knowledge and understanding of
fundamentals and typical problem areas, your experience on the job will
quickly add to your ability and confidence. Chapter 11 gives you a better
understanding of where components may be located and how they go together.
A series of photos and exploded view illustrations of the typical air conditioner,
heater and combo systems are described. Before you study them, you might
want to review the photos and drawings in earlier chapters.
Go to Chapter Start - Table of Contents - Index
10-9
11
Chapter
Click on any of these
subject headings to go
directly to the page
Typical HVAC Systems and
Components
• Heaters
• AC Units
• Heater-AC Units
• Condensers
• Sleeper Units
Now it’s time to add to your general knowledge about different systems. The
series of photos and schematics that follow show typical heater, air conditioner,
condenser and combo units. Figures 11-1 through 11-7 are also illustrated in
corresponding exploded view drawings. You can see the basic parts and how
they go together.
In most of the figures, the underhood components, plumbing, and wiring
schematics that go with the units illustrated are not shown. Their actual
position varies from one vehicle to another. Your basic mechanical knowledge is
sufficient to locate and service any parts not shown.
Figure 11-1
An auxiliary, universal
heater. It may be mounted
in various ways.
AUXILIARY HEATER
RED (LOW SPEED)
WATER OUT
HIGH
WATER IN
ORANGE (HIGH SPEED)
GROUND WIRE
OFF
LOW
TO 12 VOLT
POWER SOURCE
Go to Table of Contents - Index
11-1
Chapter 11 – Typical AC Systems and Components
UNIVERSAL HEATER/
DEFROSTER
DEFROSTER OUTLET
Figure 11-2
CORE HOUSING
A universal heater defroster
unit.
HEATER
CORE
BLOWER PLENUM
ASSEMBLY
AIR CONTROL
KNOB
BLOWER
WHEEL
WARM AIR OUTLET
BLOWER MOTOR
Figure 11-3
A universal in-cab roof
mounted air conditioner.
The compressor clutch and
condenser would probably
be mounted under the hood
or cab (cab over). Refrigeration hoses would be long
compared to in-dash
mounted units. System
controls are easily accessible for the driver. This
system is usually found on
off-road vehicles.
UNIVERSAL IN–CAB
ROOF MOUNTED AIR
CONDITIONER UNIT
PLUMBING SCHEMATIC
EXPANSION VALVE
LIQUID LINE
RECEIVERDRIER
HIGH PRESSURE LINE
SUCTION LINE
11-2
HIGH PRESSURE
LINE
TO ROOFTOP OR
FRONT MOUNTED
CONDENSER
COMPRESSOR
CLUTCH ASSEMBLY
Go to Chapter Start - Table of Contents - Index
Typical AC Systems and Components
Figure 11-4
An HVAC combination unit
designed to mount on the
panel behind the operators
seat. The vents direct air to
both the cab and rear compartment. Note how the
evaporator coil and heater
core are stacked, one over
the other. The valves and
connections are easy to
access for service.
COOL OR WARM
AIR TO REAR
(SLEEPER)
COOL OR WARM
AIR TO FRONT (CAB)
BLOWER & MOTOR
ASSEMBLY
RESISTOR
HEATER CORE
CONTROL
PANEL
EVAPORATOR
COIL
EXPANSION VALVE
WATER VALVE
AIR INTAKE
HVAC COMBINATION UNIT
DRAIN TUBE
Figure 11-5
UNIT FRONT VIEW SHOWS ACTIVE CONTROLS
This combo HVAC unit is
designed to mount under
the dash and on a specific
truck series. In this case it’s
for the MACK “R” series.
Under-dash units blend into
the overall appearance of
the dash.
MODE
SWITCH
TEMPERATURE CONTROL
AIR DIRECTION CONTROL
EXPANSION VALVE
HEATER
INLET/
OUTLET
BLOWER & MOTOR
ASSEMBLY
HVAC UNIT
CONTROL
PANEL
Go to Chapter Start - Table of Contents - Index
11-3
Chapter 11 – Typical AC Systems and Components
Figure 11-6
A basic low profile roof
mount condenser. Hoses
must be run to the compressor mounted on the engine,
and to the evaporator in the
cab.
LOW PROFILE ANGLE
MOUNTED CONDENSER
FAN & MOTOR ASSEMBLY
AIR OUT
AIR IN
LOW PROFILE ROOF MOUNT
CONDENSER COVER ASSEMBLY
WITH FAN GUARD
RESISTOR
Figure 11-7
This is an auxiliary HVAC
unit designed to heat and
cool a bunk or sleeper box.
It would supplement heat
energy movement by an
existing HVAC system. To
get engine coolant and
refrigerant to this auxiliary
system, you would “T” off
the existing refrigerant
lines and plumb the heater
in series with the cab unit,
or separately from the engine.
EVAPORATOR
COIL
OUTLET
HEATER
CORE
INLET
EXPANSION
VALVE
SOLENOID
VALVE
BLOWER & MOTOR
ASSEMBLY
AUXILIARY HVAC UNIT
Sleeper cab AC system refrigerant flow is controlled by an electrically operated solenoid valve. The solenoid is wired to the control panel in the sleeper
cab. When the operator turns on the bunk AC system, the solenoid valve opens
to allow refrigerant to flow to the evaporator mounted under the bunk. With
most installations the fan motor cycles on and off to control temperature.
Figure 11-8 shows how the sleeper box and in cab AC units may be positioned
and connected.
Note:
11-4
CTC® systems are used in some applications.
Go to Chapter Start - Table of Contents - Index
Typical AC Systems and Components
Figure 11-8
A typical installation schematic that shows component
location when under-dash
and sleeper box systems are
combined. Tee fittings in
both high and low pressure
AC lines carry refrigerant to
and from both evaporators.
The heater system is not
shown.
SLEEPER CAB
AC/HEATER
REFRIGERANT
LINES TO SLEEPER
CAB AC UNIT
IN-CAB
AC/HEATER
REFRIGERANT LINES
TO AND FROM
CONDENSER
TEE FITTINGS
COMPRESSOR
Engine intercooler designs often use the space in front of the radiator where an
AC condenser would normally be mounted. A roof mount AC system condenser
may be the solution. In some cases, there is space to install the condenser below
the intercooler. Figure 11-9 illustrates how an AC system design takes advantage of space below the intercooler for condenser installation.
Figure 11-9
This AC system schematic
shows how components
might be mounted when an
engine intercooler (chargeair cooling) has been installed in front of the
radiator. The condenser
used is designed to fit below
the intercooler unit (not
shown).
IN CAB
AC SYSTEM
CLUTCH
COMPRESSOR
CONDENSER
DESIGNED
TO MOUNT
BELOW
INTERCOOLER
RECEIVER-DRIER
Please take a few minutes to review all illustrations, cautions and notes in this
manual. If you would like more information about heavy duty vehicle HVAC
system service and repair, check with your supplier. Someone may be holding a
service clinic in your area that you could attend and benefit from.
Your own troubleshooting ability and work speed will increase with experience. Remember also, the causes for system failure can often be prevented with
a regular system maintenance program.
Go to Chapter Start - Table of Contents - Index
11-5
12
Retrofitting an R-12 System
Chapter
Click on any of these
subject headings to go
directly to the page
• Retrofit Survey
• General Retrofit Procedure
• Chapter Review
The world supply of R-12 is ever declining. Although many precautions are
being taken to contain R-12, it continues to be lost to the atmosphere. At the
same time production of this material is being curtailed. Production of R-12
will actually cease at the end of 1995.
As long as a supply exists and the price is reasonable, R-12 systems should
be serviced with this refrigerant. However, at some time, you will be retrofitting R-12 systems with R-134a. It would be a good idea to become acquainted
with the retrofit process on those vehicles you normally service. This will allow
you to discuss the process with your customer and estimate the costs involved.
The most dependable way to retrofit a system is to replace all components in
the refrigerant loop. This is costly and time consuming. Many vehicle manufacturers will recommend a retrofit procedure with a kit. Retrofit kits are planned
for vehicles produced in high volume.
Retrofit Survey
Survey the system and determine what components need changing. If a kit is
available from the original manufacturer your job is made easier. If not, review
each component and make a judgment call.
The following parts are discussed further in this section:
1. Compressor
2. Condenser
3. Receiver-Dxrier
4. Expansion Valve
5. Evaporator
6. Hoses
7. Seals and “O” Rings
8. Service Ports
1. Compressor
Some compressor manufacturers are suggesting their products can be
used with R-134a after draining out the R-12 mineral oil. Although this
may be a recommendation, it may not be backed with a warranty. Use
your own judgment here or let the customer make the call.
Go to Table of Contents - Index
12-1
Chapter 12 – Retrofitting an R-12 System
2. Condenser
When R-134a is used in an R-12 system, operating pressures generally
run about 20 psi higher. If this is acceptable, the existing condenser can be
used. If operating pressures are already marginal, as in some existing
systems, a larger condenser should be added.
3. Receiver-Drier
Always replace the receiver-drier. Many new receiver-driers are being
built with XH-7 or XH-9 desiccants which are compatible with both R-12
and R-134a. However, a drier that is in service will have collected moisture, contaminants, and lubricant. It is good insurance to start with a
clean component. R-134a is more sensitive to the presence of free moisture. A receiver-drier with more desiccant (such as 15 cubic inches in place
of 12 cubic inches) is a great idea.
4. Expansion Valve
Beginning in 1993, many expansion valves are being charged with a gas
that works equally well with R-12 and R-134a. Even a TXV charged with
R-12 will work fairly well with the new refrigerant. If the valve is clean
and functioning, it can be reused with little risk.
5. Evaporator
The evaporator coil can be used although it should be drained of lubricant.
6. Hoses
R-134a will permeate through rubber hose much faster than R-12. A nylon
barrier hose is much better for either refrigerant but essential with R134a. Nylon barrier hose has been used on many heavy duty R-12 systems. There have been continued improvements in both hoses and fitting
crimp designs. Hose replacement is costly but the customer should be
advised of the risk of possible replacement at a later date.
7. Seals and “O” Rings
Certain seals and “O” rings in older systems are not compatible with PAG
lubricants. The best bet is to change “O” rings with a known material such
as neoprene or HNBR. The systems manufacturer should be able to
advise you on compressor and other system seals.
8. Service Ports
The R-12 service ports, most often Schrader type fittings, must be removed or converted to R-134a service ports.
General Retrofit Procedure
Now it’s time to make the changeover. Before starting, be sure all the new
materials are at hand. They could well be in short supply.
12-2
Go to Chapter Start - Table of Contents - Index
General Retrofit Procedure
1. Using your R-12 recovery/recycle equipment, remove the R-12.
2. Remove mineral oil. Removing as much mineral oil as possible is
very important, although some tests indicate a residual amount of
oil can be tolerated.
3. Discard the receiver-drier.
4. Make efforts to drain those components where lubricant may
collect. This would include evaporator coils and the lowest hoses
such as those routed to a sleeper box evaporator.
5. If you are reusing the compressor, it should be removed and
drained. Measure the amount of oil removed.
6. Power flushing with R-12 might be considered, but to be successful, system restrictions (compressor, receiver drier, and expansion
valves) must be isolated. Other solvents may not be compatible
with system components, R-134a or the new lubricants. Know for
sure what you are using, and use only what is approved by the
system’s manufacturer.
WARNING
Compressed air should never be used to flush or
purge a system. Although compressed air is most dangerous in the presence of R-134a, bad habits could
develop with R-12 and carry over to the new refrigerant. Compressed air almost always contains moisture
which could result in early comebacks and additional
cost.
7. New quick connect service fittings must be installed on an R-134a
system. This is done to prevent servicing with refrigerant other
than R-134a. Figure 12-1 shows these fittings.
Figure 12-1
This illustration shows
R-134a service ports and
hose end fittings.
QUICK CONNECT HOSE END FITTING
WITH INTEGRAL SHUTOFF VALVE
SERVICE HOSE CONNECTION
DEPRESSOR PIN
SYSTEM SERVICE PORT
VALVE ASSEMBLED TO SERVICE PORT WITH VALVE IN THE OPEN POSITION
8. Reassemble the system with its new components. Attach a
vacuum pump and evacuate for at least one hour. Leak check as
discussed in Chapter 9.
9. If a label identifies the amount of R-12 and lubricant that was
used in the system, replace with that amount.
Go to Chapter Start - Table of Contents - Index
12-3
Chapter 12 – Retrofitting an R-12 System
10. If no label exists, refer to the recovery unit for lubricant withdrawn. Add the amount drained from the compressor and estimate that which was removed from other components. Add the
type of lubricant as recommended by the vehicle or compressor
manufacturer. Charge with R-134a using the sight glass technique.
11. Leak check with an electronic leak detector.
12. Replace the original system’s label with one showing the retrofit
to R-134a Include the amount of refrigerant, and the amount and
type of lubricant that was added. It is a good idea to label the
unique R-134a components if they do not already carry such
identification.
Chapter Review
Retrofitting of mobile air conditioning, systems will be a major activity by 1995.
The service technician must understand the procedure, and have the necessary
equipment and a source for the new components. Understand the step by step
procedure and do not deviate from the set plan. Advise your customer of the
potential risks of using existing components.
12-4
Go to Chapter Start - Table of Contents - Index
Glossary
accumulator — a refrigerant storage and filtering
component used in place of a receiver-drier in
CCOT air conditioner systems
activated alumina — one of the chemical agents
used in receiver-driers as a desiccant
air block — an assembly used to direct air pressure to control devices
air conditioning — control of air movement, humidity and temperature by mechanical or other
means in a vehicle
air operated water valve — a valve in the vehicle cooling (heater) system controlled by air pressure
altitude — a measured height above sea level
(where atmospheric pressure is lower than at sea
level)
ambient air temperature — air temperature
outside the vehicle
ambient switch — used to sense outside air temperature and prevent compressor operation in below freezing weather
atmospheric pressure — the pressure of the air
at a given altitude with the normal pressure reference point of 14.7 pounds per square inch at sea
level
axial compressor — a type of compressor containing pistons located in an axial design, i.e.
Frigidaire, Sanden, or Zexel (formally Diesel Kiki)
back seat — an AC service valve position which
closes off the service port and allows free flow of
refrigerant in the system
bellows — a chamber used as a control device in
an air conditioning system which expands and contracts much like an accordion
bi-level system — a cab HVAC system where the
AC output is diverted to both upper (defrost) and
lower air outlets
bimetallic — two dissimilar metals joined together to function as a thermostat
Binary™ switch — a two function pressure activated switch used to prevent compressor damage
when pressure is to high or refrigerant is lost from
the AC system
blends — a refrigerant containing less chlorine
than R-12. Proposed as a replacement for R-12, but
not a simple “drop in” substitute
blower wheel — wheel used to blow air through
the evaporator or heater core causing air to circulate in the cab
boiling point — the point at which liquid changes
to vapor
BTU — an abbreviation for British Thermal Unit,
a unit of measure of heat quantity equal to the
amount of heat energy required to raise a pound of
water one degree Fahrenheit
bulk charge — a large container of refrigerant
used in air conditioning system servicing, containing 20 or more pounds of refrigerant
CTC™ (constant temperature control), and
CTC II™ — an electro-mechanical device used to
maintain preselected air temperature
capacity — a measure of unit performance in
BTU’s per hour, tons, watts or other unit of measure
capillary tube — a gas-filled tube extending from
the thermostat and some expansion valves, senses
temperature to close thermostat (clutch) circuit or
open expansion valve orifice
Celsius — a temperature scale where zero degrees
Celsius equals 32 degrees Fahrenheit (freezing),
and 100 degrees Celsius equals 212 degrees Fahrenheit (the boiling point of water)
centigrade — another name for Celsius
change of state — the reorganization of matter
which allows a solid to change to a liquid or gas, a
liquid to a solid or gas, or a gas to a solid or liquid
Go to Table of Contents - Index
i-1
Glossary
charge — term used to describe what happens
when refrigerant is added to an air conditioning
system
charging hose — a hose connected to a port on a
manifold gauge set, used to conduct refrigerant
into the AC system from the refrigerant source
chlorofluorocarbon (CFC) — a family of chemicals which includes R-12 and other chemicals. Usage is being phased out under federal law.
clutch — a mechanical device which serves to take
the torque in a driving force and transfer it to
another force to be driven — used to drive the
compressor or engine fan
clutch cycling switch — an electrical switch
used to turn the compressor clutch on or off according to temperature or pressure demands (one example is the thermostat)
compressor — the pump (often referred to as the
heart) of an air conditioning system which pumps
refrigerant through the system and raises the vapor pressure of refrigerant
compressor head pressure — the pressure of
refrigerant as it leaves the compressor through the
discharge port
compressor shaft seal — a seal located on the
output end of the compressor shaft which serves to
keep refrigerant oil and refrigerant inside the system
condensate — the water that collects on surfaces
like the evaporator fins and other cold surfaces
when the air conditioning system is operating
condensation — the process by which gas or vapor changes to a liquid
condenser — a finned tube device (heat exchanger) in which refrigerant loses heat and
changes from hot vapor (or gas) to a warm liquid in
the system
conduction — the ability of a substance to convey
heat from one point to another within the substance (heat movement in refrigerant)
contaminant — any foreign substance (particularly moisture, dirt or air) which enters an air
conditioner system and must be removed
i-2
convection — transmitting or moving heat within
a liquid or gas by moving the heated parts
cutoff switch — a switch on the compressor which
cuts the compressor out of the system when full
throttle is applied to the engine
cycling clutch orifice tube (CCOT) system — a
Frigidaire AC system that uses an expansion tube
(fixed orifice tube) and an accumulator in place of
the expansion valve and receiver-drier
cycling clutch system — a temperature control
system which monitors the operation of the compressor clutch
dehumidify — to remove moisture (humidity)
from the air in the cab or defog the windshield
density — the ratio of mass to it’s volume
desiccant — an agent used in an air conditioning
system to dry or remove moisture by absorption;
found in the receiver-drier or accumulator
desiccant bag — the container found inside some
receiver-driers and accumulators for the desiccant
diaphragm — a device which acts as a bellows or
piston to divide the chambers of a control device
dichlorodifluoromethane — the chemical name
for Refrigerant R-12
discharge — in an air conditioning system, refers
to bleeding or releasing all refrigerant in a system
discharge line — line carrying refrigerant from
the compressor outlet to the condenser inlet connection
discharge pressure — the high side pressure (refrigerant vapor) leaving the compressor
discharge switch (compressor) — switch on the
compressor which turns the compressor off when
low pressure of refrigerant is sensed
discharge valve — same as high side service
valve
drain tube — in an AC system a tube positioned to
drain condensation out of the vehicle
Go to Glossary Start - Table of Contents - Index
Glossary
drier — normally a part of the receiver-drier, used
to absorb moisture in the system using a desiccant
as a drying agent
drive pulley — the pulley that drives the compressor clutch
drying agent — same as desiccant
electronic leak detector — a device designed to
sense leaks in an air conditioning system with extreme accuracy
electronic sight glass — a device using ultrasonic principals to sense refrigerant inside an AC
system and provide audible signals when the AC
system has the proper amount of refrigerant
filter — a portion of the receiver-drier used to
remove solid contaminants from the system
flush — the process of removing all foreign matter
from a system by means of pressurized air, refrigerant or dry nitrogen
foaming — when observed in the sight glass indicates low level of refrigerant in the system
foot-pound — a measurement of energy required
to raise one pound one foot. In relationship to
torque, it is a force that acts upon a body (such as a
bolt or nut) to produce rotation
freeze-up — the freezing of water or moisture in
the expansion valve orifice or on the fins and coil of
the evaporator
equalizer line — used to control valves in an air
conditioning system to equalize pressure or temperature
freezing point — the point at which a liquid will
become a solid
ester — a type of lubricant that may be found in R134a systems
Freon® — Dupont registered trade mark name for
refrigerant R-12
evacuate — the process of removing all moisture
or air in a system by creating a vacuum in the
system
front seat — an AC service valve position which
isolates the compressor from the system by closing
the valve (turning the valve stem all the way to the
right)
evaporation — the process by which a liquid
changes it’s state to become a vapor or gas
evaporator — a device with coils and fins through
which liquid refrigerant flows, removing heat energy from the air, and changing to a vapor
expansion tube — also called a fixed orifice tube
(CCOT system), replaces expansion valve and
meters refrigerant to evaporator
expansion valve — same as thermostatic expansion valve (TXV)
external equalizer — same as equalizer line
Fahrenheit — a scale used to measure temperature (heat intensity- how hot something is), and
calibrated at 32 degrees Fahrenheit where water
freezes and 212 degrees Fahrenheit where water
boils
fan clutch — a variable speed or on-off clutch
which acts as a coupler (fluid, air or electrical),
between engine and the engine cooling fan
gauge set — two gauges (sometimes three) installed on a manifold to test and measure conditions inside the AC system
‘H’ valve — a water valve which returns excess
coolant from the heater inlet back to the engine
cooling system
Halide leak detector — a propane gas device
used to determine the location and severity of an R12 leak in the system
head pressure — the pressure of refrigerant from
where it originates at the discharge valve of the
compressor, through all lines and components to
the orifice in the expansion valve
heat energy — heat in action; the movement of a
quantity of heat measured in BTU’s (example, in a
change of state)
heat exchanger — a device which enables fluid at
one temperature (higher) to move heat to another
fluid at a lower temperature
Go to Glossary Start - Table of Contents - Index
i-3
Glossary
heat intensity — the temperature of a substance
or material as measured by a thermometer
heat load — the amount of heat contained in a
given situation
heat quantity — the amount of heat measured in
BTU’s (British Thermal Units)
heater — an apparatus that provides heat
heater core — an assembly of metal tubing and
fins used to exchange heat from engine coolant to
cab air
Hg — the symbol used for mercury in the Periodic
Table of Elements
ideal comfort range — a temperature range, generally between 70 and 80 degrees Fahrenheit,
where most people are comfortable
in. Hg (inches of mercury) — a unit used to
measure vacuum
inch-pound — a measurement of energy required
to raise one pound one inch. In relationship to
torque, it is the force that acts upon a body (bolt or
nut) to produce rotation
in-line compressor — a 2-cylinder compressor
whose pistons are side-by-side, i.e.. Tecumseh, York
in-line drier — a drier located after the receiverdrier but before the expansion valve; absorbs and
moisture escaping from the receiver-drier
HVAC — heating, ventilation, and air conditioning
high load condition — the circumstance when
the air conditioning system is operating at maximum capacity to cool a given environment
high pressure cutout switch — a switch which
cuts out the compressor clutch if pressure in the
system rises above a pre-set level
high pressure lines — the lines that carry high
pressure refrigerant gas and liquid between the
compressor, condenser, receiver-drier and expansion valve
in-line muffler — a device to reduce noise from
the high side of the compressor
intercooler — an air-to-air heat exchanger used
on some heavy duty vehicles, that mounts in front
of the radiator to cool the intake air on a turbocharged engine. Also called a charge-air cooler
KLEA — Technical Chemical Company trademark
for R-134a
latent heat of evaporation — the amount of heat
required by a substance to change it’s state from a
liquid to a gas without raising it’s temperature
high side — the high pressure side of a system
(gas or liquid) from the compressor outlet to the
expansion valve orifice
leak detector — a device which detects any refrigerant leaks in an air conditioning system
high side low pressure cutout switch — a
switch (on the high pressure line) which cuts out
the compressor clutch if pressure in the system
drops below a pre-set level
Legris air fitting — a patented push-on connector
(fitting) used in AC/heater air control systems to
attach tubing and designed for a positive leak free
seal and quick disconnect
high side service valve — a valve on the compressor used to service the high pressure side of the
system and permit it to be checked
liquid line — the line from the outlet of the receiver-drier to the expansion valve inlet
humidity — the degree of moisture or wetness in
the air (atmosphere)
hydrochloric acid — a corrosive chemical created
within an air conditioning system when moisture
and R-12 combine under pressure
i-4
low head pressure — a system malfunction
which causes the high side pressure to be lower
than required for proper system operation
low side low pressure cutout switch — a switch
(on the suction line) which cuts out the compressor
clutch if pressure in the system drops below a preset level
Go to Glossary Start - Table of Contents - Index
Glossary
low side — the low pressure side of a system, from
the expansion valve orifice to the compressor inlet
pressure range — a measured spread between a
high and low pressure
low side service valve — a valve on the compressor used to service the low pressure side of the
system and permit it to be checked
pressure switch — a pressure sensitive electrical
switch mounted at the receiver-drier, on some accumulators or in the suction line to activate or interrupt electrical current cycling the compressor
clutch
lubricant — refrigeration oil specially formulated
to be free of all contaminants and moisture. Note:
different for R-12 and R-134a
propane — a flammable gas used in the Halide
leak detector
magnetic clutch — an electrically operated device used to cycle the compressor on and off
psi — abbreviation for “pounds per square inch”
manifold — the part of the manifold gauge device
designed to control refrigerant flow
psig — abbreviation for “pounds per square inch
gauge”
manifold gauge hoses — hoses connected to the
manifold gauge set used to test, evacuate, recover
and charge the air conditioning system
purge — to remove the refrigerant from an AC
system and hoses by opening the system or using
pressure to eliminate the contents
manifold gauge set — a system measuring device
containing two (sometimes three) gauges and three
or more service connections
R-12 — the common name of the refrigerant used
in vehicle air conditioner systems to move heat
energy
melting point — the temperature at which a solid
turns into a liquid
R-134a — a new refrigerant which does not harm
the atmosphere
mercury — used to indicate the amount of vacuum
(a perfect vacuum is 29.92 inches of mercury at sea
level)
radial compressor — a compressor that has pistons in a radial design
molecular sieve — a drying agent used in the
receiver-drier to absorb moisture and filter contaminants out of the refrigerant
natures laws — the principals of conduct in natural process or function in nature
PAG — a polyalkylene glycol lubricant used in
many R-134a systems
parallel flow — a coil design where refrigerant
flows through both upper and lower tubing at the
same time
phosgene — a poison gas produced when R-12
comes in contact with an open flame
POA valve — a suction throttling valve used in
some systems
pressure drop — pressure lost while passing
through a component, the difference between pressure in and pressure out
radiation — heat waves (heat energy) passing
through the air
radiator shutter — a metal vane assembly on
some truck radiators where the vanes can be
opened or closed to allow or exclude ram air flow to
the radiator, radiator mounted condenser and engine
ram air — air through which a vehicle passes,
increasing in force as the speed of the vehicle increases
receiver-drier — a container which receives,
stores, and removes moisture from refrigerant
reciprocating compressor — a compressor having pistons that move back and forth in cylinders
reclaim – the process of restoring refrigerant to
new product specifications
recovery – the process of removing refrigerant
from an AC system
Go to Glossary Start - Table of Contents - Index
i-5
Glossary
recycle — the process of removing contaminants
(moisture, acid, particulate matter) from a refrigerant
sight glass — a window usually in the top of the
receiver-drier for observing the condition of the
refrigerant
reed valve — suction and discharge valves located
in the valve plate of the compressor
silica gel — a type of desiccant which removes
moisture from refrigerant
refrigerant — a substance used in HVAC systems
to control heat energy
solenoid valve — an electromagnetic valve controlled by electrical current energizing and de-energizing a coil to open or close the valve
refrigerant cycle — one complete revolution of
refrigerant through the system which includes
changes of state of the refrigerant from liquid to
vapor or gas and back to liquid
specific heat — the amount of heat required to
change the temperature of one pound of a substance 1 degree Fahrenheit
refrigeration oil — a specially manufactured oil
free from moisture and all contaminants
stationery coil clutch — the magnetic clutch
used to drive the compressor
relative humidity — the amount of moisture in
the air as compared to the total amount the air can
hold at a given temperature and altitude
stem-type valve — a service valve with a
threaded valve stem for three position adjustment,
back-seated, mid position and front-seated
resistor — a voltage dropping device, usually wire
wound, which provides a means of controlling fan
or blower speed
suction line — the line connecting the evaporator
outlet to the compressor inlet; the low pressure
lines
retrofitting — reconditioning an R-12 AC system
to use R-134a
suction service valve — see “low side service
valve”
rotary vane compressor — a type of compressor
which uses internal vanes rather than pistons to
operate and pump the refrigerant through the system
suction side — the low pressure portion of the
system, from expansion valve orifice to compressor
inlet
rotating coil clutch — an old type clutch where
the magnetic coil is part of the clutch pulley — now
replaced universally by the stationary coil design
where the coil is bolted to the compressor body
sump — the portion of a compressor where oil is
contained, waiting to be circulated
superheat — heat added to a gas after evaporation from a liquid state (the approximate temperature rise across the evaporator coil)
Schrader valve — a spring loaded valve inside
some service fittings, similar to a tire valve; also
found on some accumulators
SUVA — Dupont trademark for R-134a
serpentine — a condenser coil formed from one
piece of extruded aluminum tubing
superheat switch — a switch mounted on the
compressor and connected to a thermal limiter and
fuse, used in some GM systems to sense low refrigerant and protect the compressor
service port — a fitting on control devices and
service valves allowing connection of manifold
gauge hoses
service valve — see “low side service valve” and
“high side service valve”
shaft seal — see “compressor shaft seal”
i-6
temperature range — a measured spread between a high and low temperature
thermal limiter — a protective device with a fuse
and used with a superheat switch to stop the compressor when low pressure is sensed by the superheat switch
Go to Glossary Start - Table of Contents - Index
Glossary
thermistor — a very sensitive electronic temperature sensor
thermostat — a temperature sensitive switch
used to control system temperature by cycling the
compressor on and off
thermostatic expansion valve — a valve which
senses evaporator outlet tube temperature and
pressure to regulate the flow of refrigerant into the
evaporator
TRINARY™ switch — a three function switch,
the first two functions protect the compressor from
operating as follows: 1) abnormally low refrigerant
or loss of refrigerant, 2) extremely high head pressure. The third function can open the radiator
shutter and/or cycle an air or electric operated fan
clutch when the system requires more air flow
through the condenser
tube and fin — aluminum or copper tubing inserted through individual pieces of fin material
vacuum — expressed in inches of mercury or Hg, a
vacuum is a state in which air pressure is below
atmospheric pressure
vacuum pump — a pump attached to a sealed
system or enclosure (an air conditioning system) to
evacuate air and moisture from the system
valves-in-receiver — a receiver-drier which contains an expansion valve and a POA valve in one
unit
WANKEL compressor — a type of compressor
which uses a triangular gear driven rotor inside a
figure eight shaped cavity to operate and pump
refrigerant through the AC system
water valve — a mechanical, vacuum or air operated valve used to control the flow of coolant to the
heater core
Go to Glossary Start - Table of Contents - Index
i-7
Figure Index
Fig. No.
AC/Heater Combo System Components
1
2
1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
1-9
1-10
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
5-11
5-12
AC/Heater Combo System Components .............................................. Intro-1
Typical Off-Road Installation .............................................................. Intro-2
Cab Temperature Range ............................................................................. 1-1
Heat Energy Movement - Summer/Winter ................................................ 1-2
Cab Temperature Parked - Summer/Winter .............................................. 1-3
Coolant & Refrigerant Flow Inside the Systems ....................................... 1-3
Heat Energy Radiation ............................................................................... 1-4
Thermometer - Dial Type with Probe ......................................................... 1-4
Fahrenheit/Celsius Conversion Chart ....................................................... 1-5
Change of State - Illustrated with Water ................................................... 1-5
Change of State - Effect on Refrigerant ..................................................... 1-6
Change of State - Inside AC System ........................................................... 1-7
AC/Heater Mounting Locations .................................................................. 2-2
AC System Operation - Diagram ................................................................ 2-3
Compressor Operation ................................................................................ 2-4
Clutch Assembly (to Compressor) ............................................................... 2-4
Condenser Function .................................................................................... 2-5
Receiver Drier Cutaway View ..................................................................... 2-5
Expansion Valve - Block Type Cutaway View ............................................ 2-6
Evaporator Coil with Thermostat .............................................................. 2-7
Heater System Components ....................................................................... 2-8
Pressure Radiator Cap - Thermostat Positions ......................................... 3-2
Pressure Radiator Cap - Sealing Cooling System ..................................... 3-2
Cooling System Water Pump Cutaway View ............................................. 3-3
Heater Core .................................................................................................. 3-3
Heater System Ducts - Typical ................................................................... 3-4
Blowers and Motors - Various Types .......................................................... 3-5
Heater Control Panel - Typical ................................................................... 3-5
Heater System Water Valves - Air & Cable Control .................................. 3-6
AC System Pressures & Change of State ................................................... 4-2
AC System Pressure & Temperature Relationship ................................... 4-3
Compressor Function - Low & High Side ................................................... 4-4
Compressor Designs Illustrated ................................................................. 4-5
Compressor Output (Performance) ............................................................ 4-8
Clutch Function - Thermostat Control ....................................................... 4-9
Condenser Designs - Illustrated ............................................................... 4-10
Receiver-Dryer Function ........................................................................... 4-11
Accumulator Function ............................................................................... 4-13
Internally Equalized Valve Function ....................................................... 4-14
Expansion Tube Design ............................................................................. 4-14
Evaporator Coil Function .......................................................................... 4-15
Roof Top AC System Blower & Fan Assembly ......................................... 4-16
HVAC Blend Air Duct System Cutaway View ......................................... 4-17
HVAC Stacked Core Arrangement Cutaway View .................................. 4-17
HVAC System In-Cab Control Function .................................................... 5-2
Thermostat Controls Illustrated ................................................................ 5-3
Pressure Switch/Clutch Control -Accumulator System ............................ 5-4
Refrigerant Flow Controls Illustrated ....................................................... 5-5
Heater System In-Cab Controls ................................................................. 5-7
Coolant Flow Using “H” Type Water Valve ................................................ 5-8
Air Operated Controls Cutaway View ........................................................ 5-9
Thermal Limiter/Superheat Switch Function ......................................... 5-10
Control Switch Variations Illustrated ...................................................... 5-10
Electrical Relay & Resistors Illustrated .................................................. 5-11
Electrical Schematic for Roof Mount AC System .................................... 5-11
Combination Controls - Binary™ & Trinary™ Switch Function ............ 5-12
Go to Table of Contents - Index
Page
ii-1
Figure Index
ii-2
Fig. No.
AC/Heater Combo System Components
6-1
6-2
6-3
6-4
6-5
6-6
6-7
6-8
6-9
6-10
6-11
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
8-1
8-2
8-3
8-4
8-5
8-6
8-7
8-8
8-9
8-10
8-11
8-12
8-13
8-14
9-1
9-2
9-3
9-4
9-5
9-6
10-1
10-2
10-3
11-1
11-2
11-3
11-4
11-5
11-6
11-7
11-8
11-9
12-1
Refrigerant Container Example ................................................................. 6-3
Manifold Gauge Set Function ..................................................................... 6-4
Manifold Gauge Set Hookup Location ....................................................... 6-5
Compressor Service Valves Cutaway View ................................................ 6-6
R-134a Service Ports/Hose End Fittings .................................................... 6-6
Vacuum Pumps Illustrated ......................................................................... 6-7
Leak Detector Components & Function - Halide Type ............................. 6-8
Leak Detector - Electronic .......................................................................... 6-9
Flushing Kit Components - AC System ...................................................... 6-9
Dipsticks Measure Refrigeration Oil in Compressor .............................. 6-10
Refrigerant Charging Meters & Stations Illustrated .............................. 6-11
AC System Maintenance Frequency Chart ............................................... 7-1
AC System Visual Inspection ...................................................................... 7-3
AC System Inspection - Mounting Bolts .................................................... 7-3
AC System Inspection - Fitting Leaks ....................................................... 7-5
AC System Inspection - Electrical Wiring .................................................. 7-6
AC System Cab Temperature Range Chart ............................................... 7-8
AC System Inspection - Sight Glass ........................................................... 7-9
Heater System Visual Inspection ............................................................. 7-10
Preventative Maintenance Schedule ........................................................ 7-12
System Operation Sequence ....................................................................... 8-2
Manifold Gauge Set Installation ................................................................ 8-6
Manifold Gauge Set Purging Setup ............................................................ 8-7
Manifold Gauge Set Purging Center Hose ................................................. 8-8
Troubleshooting With Gauges - Low Refrigerant Reading ..................... 8-10
Troubleshooting With Gauges - Very Low Refrigerant Reading ............. 8-11
Troubleshooting With Gauges - Air and Moisture ................................... 8-12
Troubleshooting With Gauges - Extreme Air and Moisture .................... 8-13
Troubleshooting With Gauges - TXV Stuck Closed ................................. 8-13
Troubleshooting With Gauges - TXV Stuck Open ................................... 8-15
Troubleshooting With Gauges - High Side Restriction ........................... 8-16
Troubleshooting With Gauges - Compressor Problem ............................. 8-17
Troubleshooting With Gauges - Condenser and Overcharge .................. 8-18
Troubleshooting With Gauges - Thermostat Problem ............................. 8-19
Recovery/Recycle Station Example ............................................................ 9-3
Recycled Refrigerant Pressure Chart ......................................................... 9-6
AC System Evacuation Procedure .............................................................. 9-7
Vacuum Pump .............................................................................................. 9-8
AC System Charging - Low Pressure Side (Gas Refrigerant) ................... 9-9
AC System Charging - High Pressure Side (Liquid Refrigerant) ........... 9-10
Clutch Wiring Schematic - Clutch Circuit ............................................... 10-3
Air Block Operation ................................................................................... 10-6
Constant Temperature Control System ................................................... 10-8
Auxiliary Universal Heater Illustrated ................................................... 11-1
Universal Heater/Defroster Illustrated ................................................... 11-2
Universal AC Unit Cab Roof Mount Illustrated ...................................... 11-2
HVAC Combination Unit Illustrated ........................................................ 11-3
HVAC Under Dash Installation Illustrated ............................................. 11-3
Roof Mounted Condenser - Low Profile Illustrated ................................. 11-4
Auxiliary Universal HVAC Unit Illustrated ............................................ 11-4
Sleeper Box/Truck Cab Combo System .................................................... 11-5
Intercooler Installed Above Condenser .................................................... 11-5
R-134a Service Ports/Hose End Fittings .................................................. 12-3
Go to Figure Index Start - Table of Contents - Index
Page
Subject Index
Click on page number to go to page.
Pages references in italic refer to Glossary entries.
Symbols
134a Refrigerant 4-3
A
AC accumulator system schematic 5-4
AC Active Controls 5-1
AC Clutch 2-4
AC Combination and supplemental control devices 5-1
AC components 2-3
AC Compressor 2-3, 2-4
Compressor/Clutch Assembly 2-3
AC Compressor Clutch Circuit 10-4
AC Condensation 1-6, 1-7
AC Condenser 2-5
AC Control Devices 5-1
AC Engine Coolant Flow 1-3
AC Evaporation 1-6, 1-7
AC Evaporator Coil 2-7
AC Expansion Valve 2-6
AC Gauge Readings 8-9
AC Passive Controls 5-1
AC Receiver-Drier 2-5
AC Refrigerant Flow 1-3
AC Systems and Components 11-1
AC/heater combination unit 11-3
AC/heater unit 11-3
auxiliary AC/heater unit 11-4
heater defroster unit 11-2
in-cab air conditioner 11-2
roof condenser 11-4
universal heater 11-1
Accumulator 4-12
accumulator i-1
activated alumina i-1
Air actuated fan clutches 5-13
air block i-1
Air Conditioner Blower/Fan and Motor Assembly 4-15
Air Conditioner Components 4-1
Air Conditioner Condenser 1-4, 1-6
Air Conditioner Controls 5-1
Active Controls 5-2
Compressor Clutch Control 5-3
Passive Air Conditioner Controls 5-3
Refrigerant Flow Control 5-4
Air Conditioner Hoses and Fittings 4-17
Air Conditioner System Ducts 4-16
Air Conditioner—System Operation 2-2
Condenser and High Pressure Lines 2-4
Evaporator Coil 2-6
Expansion Valve 2-6
Receiver-Drier 2-5
Air Conditioner/Heater Functions 1-7
air conditioning i-1
Air Conditioning /Heating Function 1-1
Air Conditioning System Service Tools 6-2
Flushing Kit 6-9
Heater System Service Tools 6-9
Leak Detectors 6-7
Manifold Gauge Set 6-3
Recovery/Recycling Station 6-2
Refrigerant Dispensing Valves & Containers 6-3
System Service Valves 6-5
Vacuum Pumps 6-7
Air Operated Controls—Troubleshooting 10-6
Air Block 10-7
Air Cylinder 10-7
Control Lever 10-7
Pintle 10-7
air operated water valve i-1
altitude i-1
ambient air temperature i-1
ambient switch i-1
atmospheric pressure i-1
axial compressor i-1
B
back seat i-1
bellows i-1
belt tension gauge 6-10
bi-level system i-1
bimetallic i-1
Binary™ switch 5-12, i-1
blends i-1
Blower or Fan and Motor Assembly 3-4
Blower Speed Operation 7-6
blower wheel i-1
blower/fan motor switches 5-9
boiling point i-1
British thermal units (BTU’s) 1-4, 1-5, 1-6
BTU i-1
bulk charge i-1
C
Cab Environment 1-1
Cab Temperature Levels 7-7
capacity i-1
capillary tube i-1
CAUTION 4-5, 4-12, 6-4, 6-5, 7-2, 8-6, 8-8, 89, 9-2, 10-1, 10-5
CCOT i-2
Go to Table of Contents
iii-1
Subject Index
Click on page number to go to page. Pages references in italic refer to Glossary entries.
Celsius i-1
centigrade i-1
CFC i-2
change of state i-1
Changes in Service Procedures 9-1
Changes of State 1-6
Chapter Review 1-8, 2-10, 3-6, 4-17, 5-13, 612, 7-11, 9-11
charge i-2
charging hose i-2
charging meter 6-11
charging stations 6-11
Charging the AC System 9-7
Charging with Liquid Refrigerant 9-10
Reclaiming Refrigerant 9-11
Charging with Refrigerant Gas 9-8
chlorofluorocarbon i-2
Clutch 4-8
clutch i-2
clutch cycling switch i-2
Clutch Engagemen 7-6
Clutch Engagement 7-6
Component Repair or Replacement 10-1
Compressor & Clutch 10-2
Expansion Tubes 10-2
Expansion Valves 10-2
Hoses and Fittings 10-1
Lines 10-2
Components Under the Hood 7-3
Compressor 1-7
Repair 10-3
Servicing 10-3
compressor i-2
compressor head pressure i-2
compressor service tool kits 6-10
compressor shaft seal i-2
COMPRESSORS 4-3
Types 4-5
Compressors
Compressor Output 4-7
Five-Cylinder Compressor 4-6
Four-Cylinder Compressor 4-6
Six-Cylinder Compressor 4-6
Two-Cylinder Compressor 4-6
Wankel Compressor 4-7
Conclusion 8-23
condensate i-2
condensation i-2
Condenser 2-5, 7-3
condenser i-2
Condenser types 4-10
Condensers 4-9
functions 4-9
Locations 11-5
conduction i-2
iii-2
constant temperature control i-1
contaminant i-2
Controls 3-5
convection i-2
Cooling System Thermostat 3-1
CTC™ i-1
CTC™ (Heater) and CTC™ II (Heater–A/C
System) 10-8
Air operated Water Valve 10-9
Circuit Board Assembly 10-9
Solenoid Valve 10-9
Variable Resistor 10-9
cutoff switch i-2
cycling clutch orifice tube i-2
cycling clutch system i-2
D
dehumidify i-2
density i-2
Description and Properties of Refrigerants 9-1
desiccant i-2
desiccant bag i-2
Dial Thermometer 1-4
diaphragm i-2
dichlorodifluoromethane i-2
digital thermometer 6-10
discharge i-2
discharge line i-2
discharge pressure i-2
discharge switch (compressor) i-2
discharge valve i-2
dispensing valve 1-6
drain tube i-2
drier i-3
Drive Belt 7-4
drive pulley i-3
drying agent i-3
E
electric fan clutch 5-13
electrical relay 5-11
Electrical schematic 5-10, 10-3
electrical schematic 5-11
Electrical System Inspection 7-5
Electrical Connections 7-5
Electrical Current Flow and Device Functions 7-5
electrical system inspection points 7-6
electronic digital thermometer/pyrometer 6-11
Electronic Leak Detector 6-8
electronic leak detector 6-9, 7-5, i-3
electronic sight glass 6-12, i-3
Engine Coolant or Anti-freeze 3-1
Environmental Effects on System Operation 2-9
Go to Subject Index Start - Table of Contents
Subject Index
Click on page number to go to page. Pages references in italic refer to Glossary entries.
equalizer line i-3
ester i-3
evacuate i-3
Evacuating the AC system 9-7
evaporation i-3
evaporator i-3
Evaporator Coil 4-15
expansion tube 5-5, i-3
Expansion Tubes
Expansion Tubes 4-14
expansion valve i-3
Expansion Valves & Other Metering Devices 413
Thermostatic Expansion Valves 4-13
external equalizer i-3
F
Fahrenheit i-3
fan clutch i-3
Fan Clutch or Shutter Override Circuit 10-5
filter i-3
fin comb 6-10
flush i-3
Flushing the AC System 9-6
foaming i-3
foot-pound i-3
freeze-up i-3
freezing point i-3
freon solenoid valve 5-5
Freon® i-3
Frequent AC/Heater Problems 8-21
Belts and Compressor Clutch 8-21
Condenser 8-22
Leaks, Moisture, and Adding Refrigerant 8-22
Refrigerant Lines, Hoses and Fittings 8-22
Refrigerant Metering Valves 8-22
front seat i-3
Fuses 7-6
G
gauge set i-3
GLOSSARY i-1
GM systems 4-9
H
“H” type water valve 5-8
‘H’ valve i-3
Halide leak detector i-3
halide leak detector 6-8
Halide Leak Detector (R-12 Only) 6-8
head pressure i-3
Heat and air sensing switches and solenoids 511
heat energy i-3
heat exchanger i-3
heat intensity i-4
heat load i-4
Heat Measurement 1-4
Heat Intensity 1-4
Heat Quantity 1-5
Heat Movement 1-2
Heat Movement During Changes of State 1-6
heat quantity i-4
Heat Relationships 1-6
Heat Sources 1-2
heater i-4
Heater A/C (CTC II™) & Heater (CTC™) Systems 5-8
Heater Components and Controls 3-1, 3-3, 3-4
Controls 3-5
Heater Core 3-3
Heater System Ducts 3-4
Hoses and Fittings 3-5
heater control panel 3-5
Heater Controls 5-6
Active Heater Controls 5-6
Passive (Automatic) Heater Controls 5-8
Vacuum Controls 5-8
Heater Core 1-4
heater core i-4
Heater System 1-7, 2-8
Blowers and Fans 2-9
Defrosters and Ducts 2-9
Heater Core 2-9
Water Valves 2-9
Heater system control panel 5-7
Heater System Inspection 7-9
Heater Control Valve 7-9
Other Functions 7-10
Hg i-4
high load condition i-4
high pressure cutout switch i-4
High pressure cutout switches 5-10
high pressure lines i-4
high side i-4
high side low pressure cutout switch i-4
high side service valve i-4
Hoses and Fittings 3-5
Humidity 1-7
humidity i-4
HVAC 1-7, 2-1, 2-9, i-4
HVAC control panel 5-2
HVAC Control System—Troubleshooting 10-3
HVAC duct 4-17
HVAC system 8-2
HVAC System Control Variations 5-9
Air Controls 5-9
Combination and Supplemental Controls 5-12
Electrical Devices and Schematics 5-11
Go to Subject Index Start - Table of Contents
iii-3
Subject Index
Click on page number to go to page. Pages references in italic refer to Glossary entries.
Fan Clutches, Radiator Shutters & Override
Fan Clu 5-13
hydrochloric acid i-4
P
KLEA i-4
PAG i-5
parallel flow i-5
Performance Inspection 7-7
Clutch Cycling 7-8
Sight Glass 7-8
phosgene i-5
POA valve i-5
pressure controlled txv 5-5
pressure drop i-5
pressure range i-5
pressure relief valve 5-10
pressure switch i-5
Pressure Switch Control 5-4
pressure tester 6-9
Preventive Maintenance Worksheet 7-10, 7-12
propane i-5
psi i-5
psig i-5
pulley alignment bar 6-10
purge i-5
L
R
latent heat of evaporation i-4
leak detector i-4
Legris air fitting i-4
liquid line i-4
low head pressure i-4
low pressure cutout switch 5-10
low side i-5
low side low pressure cutout switch i-4
low side low pressure switch 5-10
low side service valve i-5
lubricant i-5
R-12 4-4
R-134a 4-4
R-12 1-6, 1-7, 2-7, 4-1, 4-2, 4-3, 4-4, 4-11, 417, 5-3, 6-1, 6-2, 6-3, 6-4, 6-5, 6-6, 6-8, 69, 6-11, 7-4, 8-7, 8-9, 8-17, 8-18, 9-5, 103, 12-1, 12-2, 12-3, i-5
R-12 and R-134a 9-6
R-12 Refrigerant 4-3
R-134a 4-1, 4-2, 4-3, 4-4, 4-11, 4-17, 6-2, 63, 6-6, 6-9, 6-11, 8-7, 8-9, 9-5, 9-6, 101, 10-3, 12-1, 12-2, 12-3, 12-4, i-5
radial compressor i-5
radiation i-5
Radiator 3-2
Radiator Pressure Cap 3-1
radiator shutter i-5
Radiator shutters 5-13
ram air i-5
Receiver–Drier 4-11
Receiver-Drier 2-5, 10-2, 12-2
Receiver-drier 4-12, 4-18
receiver-drier 2-6, 2-7, 2-10, 4-4, 4-11, 4-12, 413, 4-14, 4-18, 4-19, 5-4, 5-10, 5-12, 6-9, 73, 7-8, 7-9, 8-1, 8-3, 8-12, 8-13, 8-14, 815, 8-16, 8-17, 8-18, 8-19, 8-23, 9-7, 102, 12-2, 12-3, i-5
reciprocating compressor i-5
reclaim i-5
Reclaiming Refrigerant 9-11
Recovering and Recycling the Refrigerant 9-2
Draining the Oil from the Previous Recovery
I
ideal comfort range i-4
in-line compressor i-4
in-line drier i-4
in-line muffler i-4
in. Hg i-4
inch-pound i-4
inches of mercury i-4
Inspection & Maintenance Surveys
Inspection & Maintenance Surveys 7-1
Inspection & Maintenance— without gauges 7-1
intercooler i-4
internally and externally equalized TXV’s 4-14
Introduction Intro-1
K
M
magnetic clutch i-5
manifold i-5
manifold gauge hoses i-5
manifold gauge set i-5
Manifold Gauge Set Installation 8-6
Adding Refrigerant to the System 8-7
Purging Air From Gauge Set Hoses 8-7
Stabilizing The AC System 8-9
melting point i-5
mercury i-5
molecular sieve i-5
N
natures laws i-5
Nitrogen gas 8-9
iii-4
Go to Subject Index Start - Table of Contents
Subject Index
Click on page number to go to page. Pages references in italic refer to Glossary entries.
Draini 9-3
Purging Non-Condensable Gases 9-5
Recovery Cycle Procedure 9-4
Recovery/Recycle Station 9-2
Recycling Procedure 9-5
recovery i-5
recycle i-6
Recycle station 9-3
reed valve i-6
Refrigerant i-6
refrigerant container 6-3
refrigerant cycle i-6
Refrigerants 4-1, 9-1
AC system overview 4-2
Pressure/temperature relationships 4-3
refrigeration oil i-6
Refrigeration oil dipsticks 6-10
relative humidity i-6
resistor i-6
resistors 5-11
retrofitting i-6
Roof Mounted Condensers 7-6
roof top air conditioning system 4-16
rotary vane compressor i-6
rotating coil clutch i-6
S
Safety Intro-2, 4-1, 6-1
safety 6-4
Safety Equipment 6-1
Schrader valve i-6
Schrader valve core remover/installer 6-11
serpentine i-6
service port i-6
Service Tools & Their Use 6-1
service valve i-6
Servicing and Repairing the Heater 10-9
shaft seal i-6
sight glass i-6
silica gel i-6
sleeper unit 2-1
solenoid valve i-6
special cooling system hydrometer 6-9
specific heat i-6
stationery coil clutch i-6
stem-type valve i-6
suction line i-6
suction service valve i-6
suction side i-6
sump i-6
superheat i-6
superheat switch i-6
SUVA i-6
System Component Cycling 7-7
System Controls 5-1
System Operation 2-1
T
temperature range i-6
thermal limiter i-6
thermal limiter and superheat switch 5-9
thermistor i-7
Thermostat 3-2
thermostat 3-2, i-7
thermostat tester 6-10
Thermostatic Control 5-3
thermostatic expansion valve i-7
thermostats 5-3
torque wrench 6-11
Trinary™ pressure switch 5-12
TRINARY™ switch i-7
Troubleshooting & Service Procedures 8-1
Example 8-3
Troubleshooting Overview 8-1
Troubleshooting by Manifold Gauge Set Readings 8-10
air and/or moisture 8-12
compressor malfunction 8-17
condenser malfunction or system overcharge 8-18
excessive air and/or moisture 8-13
expansion valve (TXV) stuck open 8-15
extremely low refrigerant charge 8-11
low refrigerant charge 8-10
system high pressure side restriction 8-16
thermostatic switch malfunction 8-19
xpansion valve (TXV) stuck closed or
plugged 8-13
Troubleshooting HVAC Control Systems 10-3
Binary™ and Trinary™ Switch 10-4
Truck and Heavy Equipment Systems 2-1
tube and fin i-7
V
vacuum i-7
vacuum pump i-7
vacuum pumps 6-7
vacuum tester 6-11
valves-in-receiver i-7
viscous drive fan clutch 5-13
Visual Inspection - System Off 7-2
Check for Refrigerant Leaks 7-4
Check Hoses and Fittings 7-4
Inspect Parts 7-2
Observe the System 7-2
Visual inspections 7-7
W
WANKEL compressor i-7
Go to Subject Index Start - Table of Contents
iii-5
Subject Index
Click on page number to go to page. Pages references in italic refer to Glossary entries.
WARNING 1-6, 2-7, 3-1, 4-1, 6-2, 6-3, 6-8
Water Pump 3-3
Water Valve 3-6
water valve i-7
Water Valves 5-8
X
XH-5
XH-7
XH-9
iii-6
4-11
12-2
4-11, 12-2
Go to Subject Index Start - Table of Contents
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