SERVICE - Air Conditioning, Heating & Refrigeration News

SERVICE - Air Conditioning, Heating & Refrigeration News
Published September 2012
SERVICE
TROUBLESHOOTING
With The Professor
Sponsored by:
By John Tomczyk
: HVACR Service and Troubleshooting With The Professor
Contents
About The Author
J
Chapter 1System Check Sheets................................................................ 3
ohn Tomczyk is co-author of the book
Refrigeration and Air Conditioning Technology published by Delmar, Cengage
Learning. He is author of the book Troubleshooting and Servicing Modern Air Conditioning
and Refrigeration Systems published by ESCO
Press. He is also author of an EPA-approved
Technician Certification Program Manual and a
Universal R-410A Safety and Retrofitting Training Manual. He also is a monthly columnist for Air Conditioning, Heating
and Refrigeration News magazine. Tomczyk has 28 years of teaching experience at Ferris State University in Big Rapids, Mich., along with many
years of HVACR service experience. To order the book Refrigeration and
Air Conditioning Technology, call (800) 648-7450. Tomczyk can be reached
by email at [email protected]
Chapter 2Megohmmeters for Preventive Maintenance................... 6
Chapter 3Bad Compressor Valves........................................................... 8
Chapter 4Chemical-Free Cooling Tower Treatment.......................11
Chapter 5Loss of Air Conditioning Cooling........................................14
Chapter 6Condenser Splitting.................................................................16
Chapter 7Helical Oil Separators............................................................ 20
Chapter 8Frost on the Compressor’s Head....................................... 22
Chapter 9Ice Flake Machine Troubleshooting...................................26
Chapter 10More Ice Flake Machine Troubleshooting........................28
Chapter 11Restricted TXV Metering Device....................................... 30
Published by The Air Conditioning, Heating and Refrigeration News, September
2012. Copyright © 2012, BNP Media. All Rights Reserved. No part of this book
may be reproduced or used in any manner, except as permitted by the U.S. Copyright Act, without the express written permission of the publisher. Every effort
has been made to ensure the accuracy of the information presented in this book.
However, BNP Media does not guarantee its accuracy. Any error brought to the
attention of the publisher will be corrected in a future edition. For ordering information, go to www.achrnews.com/products.
Chapter 12Basic Leak Detection Methods........................................... 33
Chapter 13Advanced Leak Detection.................................................... 37
Chapter 14Checking on Refrigerant Overcharge................................41
Chapter 15Refrigerant Migration.............................................................. 43
Chapter 16Flooding and Slugging............................................................ 46
2
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essor by John Tomczyk
: HVACR Service and Troubleshooting With The Professor
Check Sheets
System Check Sheets
T
condenser, and
in thecompares
system. subcooling
s of
Overcharged
his air
chapter
amounts inSystem
a refrigeration
�Table����Overcharged�System
Note thatsystem
all of the
system check
red
Tableof1 refrigerant,
shows an R-134a
incorporating
an overcharge
a dirty refrigconsheets used denser,
as samples
in this
artiing
eration
system
with
overcharge
and air
in the
system.
Note that
all of
the an
system
check
Item to be measured
Measured value
cle incorporate
R-134a
as
a
refrigerion
of
refrigerant.
Notice
the
30
degrees
sheets used as samples in this chapter incorporate R-134a as
Compressor discharge temperature
240˚F
ant. These systems are refrigeration
of liquid subcooling backed up in
are
a refrigerant.. These systems are refrigeration systems with a
Condenser outlet temperature
90˚F
rig- systems with a thermostatic expan- the condenser. Because of the overthermostatic expansion valve (TXV) as a metering device with receivers.
sion valve (TXV) as a metering
charge of refrigerant, the condenser
an
Evaporator outlet temperature
15˚F
device with receivers.
will have too much liquid backed
rty
Compressor inlet temperature
25˚F
Overcharged System
up in its bottom, causing high conAmbient temperature
70˚F
Table 1 shows an R-134a refrigerationdenser
systemsubcooling.
with an overcharge
of reBy overcharging
Box temperature
10˚F
system withbacked
too much
frigerant. Notice the 30 degrees of liquida subcooling
up inrefrigerant,
the conCompressor volts
230 V
increased
liquid
subcooling
amounts
denser. Because of the overcharge of refrigerant,
the
condenser
will have
too
will be
realized
in thesubcooling.
condenser. By
Compressor amps
High
much liquid backed up in its bottom, causing
high
condenser
measure it.
However, just because a system
Low side (evaporator) pressure
8.8 psig (5˚F)
overcharging a system with too much refrigerant, increased liquid subcooling
has increased subcooling amounts
amounts will be realized in the condenser.
High side (condensing) pressure
172 psig (120˚F)
in the condenser doesn’t necessarHowever, just because a system has increased
in the
ily meansubcooling
the systemamounts
is overcharged.
Item to be calculated
Calculated value
condenser doesn’t necessarily mean theThis
system
willisbeovercharged.
explained inThis
the will
next
be explained in the next two system checks.
Remember,
the condenser
is
Condenser split
50˚F
two system
checks.
Remember,
condenser
is iswhere
refrigerwhere refrigerant vapor is condensed andthe
liquid
refrigerant
formed.
This
Condenser subcooling
30˚F
ant vapor
is condensed
liquid
backed-up subcooled liquid at the condenser’s
bottom
will take upand
valuable
Evaporator superheat
10˚F
refrigerant
is
formed.
This
backedcondenser volume, leaving less volume for desuperheating and condensation
Compressor superheat
20˚F
up subcooled liquid at the condensof refrigerant vapors.
er’s bottom will take up valuable
Too much liquid subcooling at the condenser’s bottom will cause unwanted
compressor discharge temperatures will also be realized from the higher heat
condenser volume, leaving less
inefficiencies by raising the head pressurevolume
and the compression
ratio. Higher
of�Table����System�With�A�Dirty�Condenser
compression caused from the high compression ratio.
for desuperheating
and
compression ratios cause lower volumetric
efficiencies and
lower mass
flow
Remember, most conventional condensers’ functions are to:
condensation
of refrigerant
vapors.
Item to be measured
Measured value
rates of refrigerant through the refrigeration
Higher subcooling
superheatedat
• Desuperheat compressor discharge vapors,
Toosystem.
much liquid
Compressor discharge temperature
250˚F
the condenser’s bottom will cause
110˚F
unwanted inefficiencies by raising 3 Condenser outlet temperature
www.achrnews.com
the head pressure and the
comEvaporator outlet temperature
10˚F
pression ratio. Higher compression
Compressor inlet temperature
25˚F
ratios cause lower volumetric effi-
ut of the
ge and into
tal Age
Ambient temperature
70˚F
ge and into
tal Age
Condenser subcooling
30˚F
ant vapor is condensed and liquid
Evaporator superheat
10˚F
refrigerant is formed. This
backed: HVACR
Service and Troubleshooting With The Professor
Compressor superheat
20˚F
up subcooled liquid at the condenser’s bottom will take up valuable
• Condense these vapors to liquid, andcondenser volume, leaving less
�Table����System�With�A�Dirty�Condenser
• Subcool refrigerant at its bottom. volume for desuperheating and
condensation of refrigerant vapors.
Item to be measured
Measured value
Too much liquid subcooling at
System with Dirty Condenser the condenser’s bottom will cause
Compressor discharge temperature
250˚F
Table 2 shows a refrigeration system
with a dirty
condenserbycausing
Condenser outlet temperature
110˚F
unwanted
inefficiencies
raising
restricted airflow over the condenser. Athe
similar
deheadcondition
pressurewould
and be
thea comEvaporator outlet temperature
10˚F
fective condenser fan motor starving thepression
condenser
of air.
Bothcompression
conditions
ratio.
Higher
Compressor inlet temperature
25˚F
caused the head pressure and thus condensing
temperature
to increase.
ratios cause
lower volumetric
effiAmbient temperature
70˚F
ciencies
lower because
mass flow
Even the liquid at the condenser’s bottom
will and
be hotter
of rates
the
Box temperature
15˚F
refrigerant
through
the refrigelevated condensing temperatures. Thisof creates
a greater
temperature
Compressor volts
230 V
eration system.
Higher
superheated
difference between the liquid at the condenser’s
bottom
and the
ambient
compressor discharge temperatures
Compressor amps
High
(surrounding air) designed to cool the condenser and its liquid. This will
will also be realized from the higher
Low side (evaporator) pressure
6.2 psig (0˚F)
cause the liquid at the condenser’s bottom to lose heat faster, causing
heat of compression caused from
High side (condensing) pressure
185.5 psig (125˚F)
more condenser subcooling. In this example,
highcompression
condenser subcooling
the high
ratio. (Forisa
not caused from an “amount” of liquid being
in the
condenser,
reviewbacked
of howup
much
condenser
subItem to be calculated
Calculated value
but from the liquid in the condenser’s bottom
losinginheat
faster. see
coolingsimply
is needed
a system,
Condenser split
55˚F
“The
Needed Amount
of Condenser
This phenomenon happens because the
temperature
difference
between
Subcooling,”
in theambient
April 2,is 2012,
Condenser subcooling
15˚F
the liquid at the condenser’s bottom and
the surrounding
the
edition
of
The
NEWS.)
driving potential for heat transfer to take place. As more and more air is
Evaporator superheat
10˚F
Remember, most conventional
restricted from flowing through the condenser, the amount of condenser
Compressor superheat
25˚F
condensers’ functions are to:
subcooling will increase.
• Desuperheat compressor disNotice that the system check sheet shows
higher
than normal condenser
larities of symptoms in both scenarios of an overcharge of refrigerant and
charge
vapors,
�Table����System�Containing�Air
subcooling of 15˚. This system check sheet• looks
very similar
an over-to
restricted
airflow over the condenser.
Condense
these tovapors
charge of refrigerant because of the increased
amounts, but do
liquid, subcooling
and
Item to be measured
Measured value
• Subcool
at its
not be fooled by it. When a high head pressure
and high refrigerant
condenser subcoolSystem
Containing Air
Compressor discharge temperature
235˚F
bottom.
ing is experienced in a refrigeration system,
the service technician must not
Another similar scenario would be a refrigeration system containing air,
Condenser outlet temperature
85˚F
assume an overcharge of refrigerant. The technician must first check to see
as in Table 3. Air is a noncondensable and will get trapped in the top of the
System with Dirty Condenser condenser.
Evaporator outlet temperature
17˚F
if the condenser is dirty or a condenser fan is inoperative because of simiThis will cause high head pressures and high condensing temperTable 2 shows a refrigeration
Compressor inlet temperature
40˚F
system with a dirty condenser caus- 4
Ambient temperature
75˚F
ing restricted airflow over the
conwww.achrnews.com
Box temperature
15˚F
ficiency
denser. A similar condition would
Compressor volts
230 V
be a defective condenser fan motor
uire tight
starving the condenser of air. Both
Condenser subcooling
edition of The NEWS.)
Evaporator superheat
Remember, most conventional
: HVACR Service and Troubleshooting With The Professor
Compressor superheat
condensers’ functions are to:
• Desuperheat compressor discharge vapors,
�Table����System�Containing�Air
• Condense these vapors to
liquid, and
Item to be measured
• Subcool refrigerant at its
Compressor discharge temperature
bottom.
This phenomenon happens because the
temperature difference between the liquid at
the condenser’s bottom and the surrounding
ambient is the driving potential
for heat transfer
System with Dirty Condenser
Table 2air
shows
a refrigeration
to take place. As more and more
is restricted
system with a dirty condenser causfrom flowing through the condenser,
the amount
ing restricted airflow
over the conficiency
denser. A similar condition would
of
condenser
subcooling
will increase.
be a defective condenser fan motor
uire tight
starving the condenser of air. Both
sto Digital
conditions
caused thecondense,
head pressure
to desuperheat,
and
er! atures because of reduced condenser volume
andbottom
thus condensing
temperature
subcool. Thus, the liquid at the condenser’s
will be hotter
than noriability
to
increase.
Even
the
liquid
at the
Approved
for the ambient. This will result in an increase
faster to
oolingmal and will lose heat
use in CheckMe!®
condenser’s bottom will be hotter
es
in condenser subcooling.
programs
because of the elevated condensing
at pump operation
Table 3 shows 40˚ of condenser subcooling, but these amounts will vary
temperatures. This creates a greater
depending on the amount of air in the system.
temperature difference between the
SA.com/refrigeration
Again, in this example, high condenserliquid
subcooling
not caused from
an
at theis condenser’s
bottom
“amount” of liquid being backed up in the
condenser,
but from
the liquidair)
in
and
the ambient
(surrounding
condenser’s bottom simply losing heatdesigned
faster. to cool the condenser and
#14 at the
achrnews.com
15˚F
10˚F
25˚F
Measured value
235˚F
Condenser outlet temperature
85˚F
Evaporator outlet temperature
17˚F
Compressor inlet temperature
40˚F
Ambient temperature
75˚F
Box temperature
15˚F
Compressor volts
230 V
Compressor amps
High
Low side (evaporator) pressure
8.8 psig (5˚F)
High side (condensing) pressure
185.5 psig (125˚F)
Item to be calculated
Calculated value
Condenser split
50˚F
Condenser subcooling
40˚F
Evaporator superheat
12˚F
Compressor superheat
35˚F
Air Conditioning, Heating & Refrigeration NEWS | May 7, 2012
5/1/12 11:52 AM
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: HVACR Service and Troubleshooting With The Professor
Megohmmeters for Preventive Maintenance
M
egohmmeters (meggers) are electrical meters used to
check the resistance and condition of the motor windings
and the condition of the refrigeration and oil environment
around the motor windings. A megger is nothing but a giant ohmmeter that creates a very large dc voltage (usually
500 volts dc) from its internal battery. The meter will read out in megohms
(millions of ohms). Any motor winding or electrical coil can be checked with
a megger. A megohmmeter’s main function is to detect weak motor winding
insulation and to detect moisture accumulation and acid formations from
the motor windings to ground before they can cause more damage to motor
winding insulation.
When dealing with HVACR hermetic and semi-hermetic compressor motors, as contaminants in the refrigerant and oil mixture increase, the electrical resistance from the motor windings to ground will decrease. Because of
this, regular preventative maintenance checks can be made with a megohmmeter and can signal early motor winding breakdown from a contaminated
system when accurate records are kept.
One probe of the megger is connected to one of the motor winding terminals, and the other probe to the shell of the compressor (ground). Note:
Make sure metal is exposed at the shell of the compressor where the probe
is attached so that the compressor’s shell paint is not acting as an insulator to
ground. When a button is pushed and held on the megger, it will apply a high
dc voltage between its probes and measure all electrical paths to ground. It is
important to disconnect all wires from the compressor motor terminals when
megging a compressor motor.
Figure 1.
Also, read the instructions that come with the meter to determine what
time interval to energize the megger when checking winding or coils. If possible, it is a good idea to run the motor for at least one hour, disconnect
power, disconnect all electrical leads, and then quickly connect the megger
to the motor. This will give a more meaningful comparison between readings
for the same compressor on different days, because of the approximate same
winding temperatures.
Good motor winding readings should have a resistance value of a minimum of 100
megohms relative to ground. In fact, good motor winding resistance should be between 100 megohms and infinity.
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: HVACR Service and Troubleshooting With The Professor
Regular preventative maintenance checks
can be made with a megohmmeter and
can signal early motor winding breakdown
from a contaminated system when accurate
records are kept.
tion, moisture, or other system contamination.
Listed below are some other important tips service technicians should
know about the use of a megohmmeter:
• Never use a megger if the motor windings are under a vacuum.
• Meggers can be used for other electrical devices other than electric motors.
• Always consult with the meter manufacturer or user’s manual for detailed instructions on megging other electrical devices like coils.
• Meggers are often used in preventive maintenance programs, especially
before a contractor signs a preventive maintenance contract to determine
condition of the electrical devices.
• Any megger with a higher voltage output than 500 volts DC should be
used by an experienced technician. A high voltage for too long of a time may
further weaken or fail motor windings and the winding insulation could be
damaged by the testing procedure.
Figure 1 lists megohm readings with varying degrees of contamination and
motor winding breakdown. Because of the very high resistance of the motor
winding insulation, a regular ohmmeter cannot be used in place of the megger. A regular ohmmeter does not generate enough voltage from its internal
battery to detect high resistance problems like deteriorated winding insula-
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: HVACR Service and Troubleshooting With The Professor
M
Bad Compressor Valves
any servicemen experience service calls where the compressor has both a low head pressure and a high suction
pressure. Often, the refrigeration equipment is still running,
but the product temperature is suffering about 7 to 10°F.
These calls are tough to handle because the compressor is
still cooling, but not cooling to its rated capacity. The medium-temperature
products will spoil quicker and the low-temperature products are not frozen
as solid as they should be.
There are three main reasons why a compressor will simultaneously have
a low head pressure and a high suction pressure:
• Bad (leaky) compressor valves (Figure 1);
• Worn compressor rings (Figure 2); and
• Leaky oil separator.
• TXV set wrong — Too much superheat causing compressor overheating;
• Undercharge causing high superheat and compressor overheating; and
• Low load on the evaporator from a frozen coil or fan out causing slugging or flooding of the compressor.
Below is a service checklist for a compressor with valves that are not sealing.
Compressor With Leaky Valves
(Measured Values)
Compressor discharge temp...................................225˚
Condenser outlet temp.............................................75˚
Evaporator outlet temp............................................25˚
Compressor in temp.................................................55˚
Ambient temperature..............................................75˚
Box temperature.....................................................25˚
Compressor volts....................................................230
Compressor amps................................................... low
Lowside (evaporating) pressure (psig)...... 1.6 psig (10˚)
Highside (condensing) pressure (psig)....... 95 psig (85˚)
Leaky Compressor Valves
Here are reasons why a compressor’s valves may become inefficient because of valve warpage from overheating or lack of lubrication, or from having
carbon and/or sludge deposits on them preventing them from sealing properly.
• Slugging of refrigerant and/or oil;
• Moisture and heat causing sludging problems;
• Refrigerant migration problems;
• Refrigerant flooding problems;
• Overheating the compressor which may warp the valves;
• Acids and/or sludges in the system deteriorating parts;
• TXV set wrong — Too little superheat causing flooding or slugging;
(Calculated values ˚F)
Condenser split.........................................................10
Condenser subcooling...............................................10
Evaporator superheat...............................................15
Compressor superheat..............................................45
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: HVACR Service and Troubleshooting With The Professor
Symptoms include:
•
•
•
•
•
•
Higher than normal discharge temperatures;
Low condensing (head) pressures and temperatures;
Normal to high condenser subcooling;
Normal to high superheats;
High evaporator (suction) pressures; and
Low amp draw.
Higher than normal discharge temperatures: A discharge valve that
isn’t seating properly because it has been damaged will cause the head pressure to be low (Figure 1). Refrigerant vapor will be forced out of the cylinder
and into the discharge line during the upstroke of the compressor. On the
downstroke, this same refrigerant that is now in the discharge line and compressed will be drawn back into the cylinder because the discharge valve is
not seating properly. This short cycling of refrigerant will cause heating of the
discharge gases over and over again, causing higher than normal discharge
temperatures. However, if the valve problem has progressed to where there
is hardly any refrigerant flow rate through the system, there will be a lower
discharge temperature from the low flow rate.
Low condensing (head) pressures: Because some of the discharge
gases are being short cycled in and out of the compressor’s cylinder, there
will be a low refrigerant flow rate to the condenser. This will make for a
reduced heat load on the condenser thus reduced condensing (head) pressures and temperatures.
Normal to high condenser subcooling: There will be a reduced refrigerant flow through the condenser, thus through the entire system because
components are in series. Most of the refrigerant will be in the condenser and
receiver. This may give the condenser a bit higher subcooling.
Figure 1. Overheating and discoloring of a discharge valve.
(All photos courtesy Ferris State University.)
Normal to high superheats: Because of the reduced refrigerant flow
through the system, the TXV may not be getting the refrigerant flow rate it
needs. High superheats may be the result. However, the superheats may be
normal if the valve problem is not real severe.
High evaporator (suction) pressure: Refrigerant vapor will be drawn
from the suction line into the compressor’s cylinder during the downstroke
of the compressor. However, during the upstroke, this same refrigerant may
sneak back into the suction line because the suction valve is not seating properly. The results are high suction pressures.
Low amp draw: Low amp draw is caused from the reduced refrigerant flow
rate through the compressor. During the compression stroke, some of the re-
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: HVACR Service and Troubleshooting With The Professor
frigerant will leak through the suction valve
and back into the suction line reducing the
refrigerant flow. During the suction stroke,
some of the refrigerant will sneak through
the discharge valve because it is not seating properly, and get back into the compressor’s cylinder. In both situations, there
is a reduced refrigerant flow rate causing
the amp draw to be lowered. The low head
pressure that the compressor has to pump
against will also reduce the amp draw.
sor crankcase through a small return line.
The pressure difference between the high
and low sides of the refrigeration system
is the driving force for the oil to travel
from the oil separator to the compressor’s crankcase.
The oil separator is in the high side
of the system and the compressor crankcase in the low side. The float-operated
oil return needle valve is located high
enough in the oil sump to allow clean oil
to automatically return to the compressor’s crankcase.
Only a small amount of oil is needed
to actuate the float mechanism, which
ensures that only a small amount of oil is
ever absent from the compressor crankcase at any given time. When the oil level in the sump of the oil separator drops
to a certain level, the float forces the
needle valve closed. When the ball and
float mechanism on an oil separator goes
bad, it may bypass hot discharge gas directly into the compressor’s crankcase.
The needle valve may also get stuck partially open from grit in the oil. This will cause high pressure to go directly
into the compressor’s crankcase causing high low-side pressures and low
high-side pressures.
Worn Compressor Rings
When the compressor rings are worn,
high-side discharge gases will leak through
them during the compression stroke, giving
the system a lower head pressure (Figure
2). Because discharge gases have leaked
through the rings and into the crankcase, the
suction pressure will also be higher than normal. The resulting symptom will be a lower
head pressure with a higher suction pressure.
The symptoms for worn rings on a compressor are very similar to leaky valves.
Figure 2: Worn compressor rings.
Leaky Oil Separator
When the oil level in the oil separator becomes high enough to raise a
float, an oil return needle is opened, and the oil is returned to the compres-
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: HVACR Service and Troubleshooting With The Professor
Chemical-Free Cooling Tower Treatment
P
ure water is a rare commodity. Water, as
and attraction of particles eventually becomes hard,
we know it, contains many dissolved minerequipment-damaging scale.
als. When evaporation occurs in a cooling
Now, a proprietary and patented technology has
tower, only the water evaporates; it exits
been developed by an engineering and research team.
the cooling tower as water vapor, but leaves
This chemical-free technology eliminates scale, inhibits
the minerals behind to concentrate in the cooling tower’s
bacterial growth, and inhibits corrosion in water purifiwater system.
cation (Figure 1).
The concentrations of these dissolved minerals
gradually increase until a process called precipitation
How it Works
occurs. Precipitation happens when dissolved minerWhen the cooling tower water holding these small
als such as calcium carbonate (limestone) reach a cersuspended particles passes through a water treatment
tain concentration and become solid, usually clinging
module and is activated by a high-frequency electrical
to equipment and piping surfaces in the cooling tower.
pulse field, the natural electrical static charge on the
HVACR personnel refer to these solids as scale.
particle’s surface is removed.
Tiny suspended particles exist in large quantities
In removing this surface charge on the suspended
in all city water, or well water that is used for coolparticles, they are now the preferred site for precipiing tower or boiler makeup water. Once in the cooling
tation of minerals to occur, instead of the equipment
tower water system, these suspended particles neither
surfaces. The suspended particles now act as seeds
sink nor float because of their small size. They are
for precipitation of dissolved minerals. Thus, the hard
transported by the flowing water.
scale is prevented from forming on the equipment’s
The particles will concentrate during the evapora- Figure 1. Signal generator and water treatment
surfaces and instead bonds to the tiny suspended parmodule installed in a working cooling tower.
tion process and be attracted to the equipment sur- (Courtesy of Clearwater Systems Corp.)
ticles in the water.
faces in the cooling tower. When the concentration is
The minerals in the water now adhere to and coat
so great that the water can hold no more minerals, they are forced to find
the suspended particles. As more and more minerals bond to the suspendsurfaces to precipitate to as a solid, scaling the equipment. This concentration
ed particles, they become heavier and can no longer suspend themselves in
11
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: HVACR Service and Troubleshooting With The Professor
Figure 2 (left). The removal of
particles at the bottom of the
cooling tower’s basin can be
accomplished using a centrifugal
separator. (Courtesy of Lakos
Separators and Filtration Solutions)
the water stream. They eventually make their way to the cooling
tower’s basin as a harmless fluffy
powder or tiny coated particle.
This powder or coated particle
can easily be removed from the
cooling tower’s basin by manual
means, filtration, or centrifugal
separation. The quantity of powder
is typically about 15 percent of normal blow-in dirt in a cooling tower.
strength. Particles in the water are
now separated through centrifugal
action caused by the vortex. The
particles spiral downward along
the perimeter of the inner separation barrel and are deposited in a
collection chamber below the vortex deflector plate, where they can
be automatically purged.
Free of separable particles, the
water spirals up the center vortex
in the separation barrel and upward to the outlet. A vortex-driven pressure relief line draws fluid
from the separator’s solids-collection chamber and returns it to
the center of the separation barrel at the vortex deflector plate.
This allows even finer solids to be
drawn into the solids-collection
chamber that would otherwise be
re-entrained in the vortex.
Particle Separator
Particles can be removed
from the bottom of the cooling
tower’s basin using a centrifugal
separator (Figure 2). Water from
the basin is pumped to a centrifugal separator, where it enters the
separator tangentially. This gives
the water the proper inlet velocity and causes a constant change
of direction to generate an initial
vortexing action.
Internal tangential slots located on the inner separation barrel causes the water to accelerate
further and magnify the vortex
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Bacterial Control
a 24- to 48-hour life span. Any microbe not captured in the forming powder
are zapped by the secondary pulse of the signal generator, forcing them to
spend their lives repairing cell wall damage rather than reproducing.
All of the living organisms in a cooling tower system depend on one another for their food supply. Thus, when the nutrients from the planktonic bacteria
are diluted by both encapsulation and electroporation, the biofilm cannot be
sustained and it will disintegrate.
The biofilm will never be created if the cooling tower system is installed
using a high-frequency electrical pulse field and creating encapsulation and
electroporation processes. The combined effects of encapsulation and electroporation result in exceptionally low total bacterial counts (TBC) in cooling tower water.
There are two methods of controlling bacteria or microbial population in
cooling tower systems: encapsulation and electroporation.
Normally, bacteria form a biofilm or slime layer on equipment surfaces.
The slimy bacterial secretion forms a protective canopy to protect the bacteria beneath it from chemical biocides. It is very slimy to the touch, four times
more insulating to heat transfer than mineral scale, and is the primary cause
of microbial-influenced corrosion on equipment.
The bacteria that live in a biofilm and adhere to the equipment surfaces
are called Sessile bacteria; they represent 99 percent of the total bacteria
in a system. However, this slime layer can be eliminated through a process of
nutrient limitation.
The suspended particles in the water of a cooling tower incorporate
most of the free-floating planktonic bacteria. Normally, since like charges
repel one another, the bacteria are repelled by the suspended particles in
cooling tower water due to the fact that nearly all tiny particles have similar
negative static electrical charges on their surfaces. However, after being
activated by the high-frequency electrical pulse field at the water treatment
module by the signal generator, the natural electrical static charge on the
particle’s surface is removed.
The repulsion to the bacteria is eliminated; therefore, the bacteria are
attracted to the powder and become entrapped in it. The powder, in effect,
sweeps the water clean of planktonic bacteria and renders them incapable of
reproducing. This process is referred to as encapsulation.
The high-frequency, pulsing action of the signal generator also damages
the membrane of the planktonic bacteria by creating small pores in their outer
membrane. The condition weakens the bacteria and inhibits their capabilities
to reproduce. This process is referred to as electroporation. Microbial life has
Corrosion Control
Most corrosion in cooling tower systems or boilers comes from:
• Chemical additives;
• Softened water;
• Biofilm; and
• Mineral scale.
So, by removing chemicals, avoiding the use of softened water, and using
the chemical-free water treatment module and signal generator in cooling
tower and boiler water applications, corrosion concerns can be eliminated.
The calcium carbonate that coats the suspended particles is in a state
of saturation while it precipitates, and will act as a powerful cathodic corrosion inhibitor. It will greatly slow the corrosion process by blocking the
reception of electrons that are thrown off by the corrosion process. With
no place for the electrons to go, the corrosion process is physically, very effectively controlled.
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F
Loss of Air Conditioning Cooling
or this chapter I want to discuss a real life situation regarding
poor cooling in a residence and reduced airflow coming from the
registers in the house. The air conditioner is a three ton (36,000
btuh), HCFC-22, split type, air conditioner with the A-coil in the
plenum of the furnace located in the basement. The evaporator
has an orifice for a metering device. The condensing unit is located on the
east end of the house. The residence is a 1,800-square-foot ranch house located in a subdivision in Flint, Mich. The homeowners are an elderly couple
and rely on air conditioning for health reasons. It has been an unseasonably
hot summer and temperatures in the house are reaching 80˚F. In fact, the
homeowners said that temperatures inside the house have been rising steadily
in the last two weeks. They try to keep the house at 72˚ throughout the entire
summer. They are also complaining of high humidity inside the house.
A service technician soon arrives. After introducing himself and his company, the technician converses with the two homeowners for about 10 minutes
trying to get as much information and history about the a/c problem as possible.
The technician then goes outside to the condensing unit and installs both of his
gauges. He instantly notices that the suction pressure is reading 50 psig (26˚).
The normal suction pressure should be about 70 psig (41˚) for the outdoor temperature and humidity conditions that day. The head pressure is also low at 190
psig for the 90˚ day. The head pressure should be in the 255–265 psig range.
The technician also notices the compressor sweating heavily from top to bottom.
The technician then touches the crankcase area or bottom to the compressor and finds that it is extremely cold. This means that the compressor has
been suffering from liquid floodback during the day at some point during its
Equation 1.
run cycle. Floodback is liquid refrigerant entering the crankcase of the compressor during the running cycle. The technician then installs a temperature
probe on the suction line about 6 inches from where it enters the compressor. The temperature reads 28˚. The technician then subtracts the saturated
evaporating temperature of 26˚ from the compressor inlet temperature 28˚
and finds out that there is only 2˚ of compressor superheat (See Equation 1).
This reinforces that there is a floodback problem during the running cycle.
Floodback can ruin a compressor by diluting the compressor’s oil with liquid
refrigerant. This has a tendency to ruin the lubricity of the oil and score bearing surfaces in the compressor. Floodback also causes oil foaming, which can
cause oil to be pumped out the discharge valve and into the system. Discharge
valve damage can also occur from the oil foam/refrigerant rich mixture.
Finding a Cause
The technician then checks the airflow problem and agrees with the homeowners that there is a reduced airflow problem. The technician then takes a cur-
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rent reading of the fan motor and finds it to be 4.2 amps. This is far from the
nameplate current of 8 amps. This tells the technician that the fan motor is only
partially loaded and is not moving the proper amount of air it is designed to move.
The technician then decides to check the air filter located in the return air
cabinet before the evaporator or A-coil. He notices that it is completely filled
with dust and lint. However, even with the air filter pulled, there still is a restricted airflow problem and the fan motor continues to pull low current. He
then decides to have a look at the A-coil itself. He shuts off power to the unit
and removes the plenum. He finds that the A-coil is completely covered with
a blanket of ice and frost. The technician then melts the iced coil with a large
wattage blowdryer. After putting the plenum back on the unit and installing a
new air filter, the technician starts the air conditioner. The proper airflow has
been established and the suction pressure is normal at 70 psig. The fan motor
is now drawing normal current of about 7 amps.
The technician then explains to the homeowner that a dirty air filter has
caused a restricted airflow to the A-coil. He then explains the importance of
keeping the air filter clean. This restriction in the airflow has caused a low
suction pressure because of a reduced heat load entering the evaporator coil.
This caused a slower vaporization rate of refrigerant in the evaporator. The
low suction pressure made the refrigerant flowing through the evaporator
below freezing (26˚). This finally froze the evaporator coil solid with ice. The
restricted airflow also unloaded the fan motor causing it to draw low current.
Once the evaporator coil froze solid, the refrigerant saw very little heat
and humidity load. This caused a low vaporization rate and some of the liquid
refrigerant (R-22) trickled down the suction line to the compressor’s crankcase causing floodback. This is why there were only 2˚ of compressor superheat and the crankcase area was cold to the touch.
The low heat and humidity load on the evaporator also caused the head
pressure to be low. This happened because if there was very low heat being absorbed in the evaporator section, there will be hardly any heat to be
rejected into the condenser section of the system. This will keep condensing
(head) pressures down.
Talk Is Good
Many technicians will try to add refrigerant when they experience low suction and low head pressures simultaneously. This is not always the answer. It is
true, an undercharge of refrigerant will cause low head and low suction pressures, but that is not the only thing that will cause both pressures to be low.
An undercharge will have low subcooling readings on the high side, where a
dirty air filter for the evaporator will not produce low subcooling readings.
In this case, something as simple as a dirty air filter was the culprit in
freezing the coil and causing low head and suction pressures. In this case,
the low airflow was the major clue to the problem, and it wouldn’t have been
noticed if the technician did not converse with the homeowner before troubleshooting. Hopefully, the service technician would have eventually taken a subcooling reading if the low airflow problem was not noticed.
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T
Condenser Splitting
his chapter focuses on the concept of condenser splitting.
But first, here’s a quick review of condenser flooding before
covering condenser splitting to help the reader better understand both of these concepts and their particular advantages
and disadvantages.
Condenser Flooding
A pressure-actuated holdback valve is installed at the condenser outlet.
This valve is often referred to as an ORI (Open on Rise of Inlet) valve. The
valve will throttle shut when the condenser pressure reaches a preset minimum pressure in a cold ambient condition (Figure 1). This throttling action
will back up liquid refrigerant in the bottom of the condenser, causing a flooded condition. The condenser now has a smaller internal volume, which is what
is needed for a colder ambient condition. The condenser pressure will now
rise, giving sufficient liquid line pressures to feed the expansion valve. Larger
receivers are needed for these systems to hold the extra refrigerant for condenser flooding in the summer months.
While the condenser is being flooded with liquid refrigerant, a CRO (Close on
Rise of Outlet) valve, located between the compressor’s discharge line and the
receiver inlet, will bypass hot compressor discharge gas to the receiver inlet when
it senses a preset pressure difference between the discharge line and the receiver
(Figure 1). The ‘T’ symbol means the valve comes with a built-in pressure tap for
ease in taking a pressure reading for service purposes and for setting the valve.
The pressure difference is created from the reduced flow of refrigerant to the
receiver because of the throttling action of the ORI valve. The bypassed hot gas
Figure 1. The Close on Rise of Outlet (CRO) valve is located between the
compressor’s discharge line and the receiver inlet. (All artwork courtesy
Sporlan Division, Parker Hannifin Corp.)
through the CRO valve serves to warm up any cold liquid coming from the ORI
valve at the receiver’s inlet, and it will also increase the pressure of the receiver
so metering devices will have the proper liquid line pressure feeding them.
One of the main advantages of condenser flooding is to keep consistent liquid pressure feeding the metering device in low ambient conditions. Manufac-
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Figure 2. One way to reduce the
amount of extra refrigerant charge
needed for condenser flooding is to
split the condenser into separate
and identical condenser circuits.
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Figure 3 (left). The splitting of the condensers is done with the addition
of a pilot-operated, three-way solenoid valve installed in the discharge
line from the compressors.
turers do supply technical information on how much
extra refrigerant is needed for flooding a condenser
for a certain low ambient condition. However, in
extreme low ambient conditions, it may be necessary to flood 80 to 90 percent of the condenser. On
larger systems, this could mean several hundred pounds
of refrigerant. This is the main disadvantage of flooding
a condenser for low ambient operations. With the rising
price of refrigerant and the environmental concerns of
global warming and ozone depletion, condenser flooding
can become quite expensive and environmentally unsound if
not managed and serviced properly.
denser is referred to as the summer condenser (Figure 2). The threeway solenoid valve controlling the splitting of the condensers can be
energized and de-energized by a controller sensing outside ambient
conditions, an outdoor thermostat, or a high-side pressure control.
During summertime operations, the added surface area and volume of both condensers are needed to maintain a reasonable head
pressure at higher ambient conditions. The pilot-operated, three-way
solenoid valve is then de-energized. This positions the
main piston inside the valve to let refrigerant flow
from the compressor’s discharge line to the threeway valve’s inlet port, and then equally to the valve’s
two outer ports. In other words, the flow of refrigerant will flow to both of the condenser halves equally.
In low ambient conditions, the summer portion of the condenser
can be taken out of the active refrigeration system by the three-way
valve. When the coil of the pilot-operated, three-way solenoid valve
is energized, the sliding piston inside the valve will move and close off
the flow of refrigerant to the port on the bottom of the valve that feeds
the summer condenser. This action will render the summer condenser
inactive or idle, and the minimum head pressure can be maintained by
flooding the summer-winter half of the condenser with conventional refrigerant-side head pressure control valves, as explained in the condenser
flooding section of this chapter.
In fact, during winter operations, the system’s head pressure is best maintained with a combination of condenser splitting, refrigerant-side head pressure
Condenser Splitting
As mentioned above, the main disadvantage of
condenser flooding is that larger refrigeration systems may hold hundreds of extra pounds of refrigerant needed to properly flood a condenser at extremely low ambient conditions. One way to reduce the amount of extra refrigerant
charge needed for condenser flooding is to split the condenser into two
separate and identical condenser circuits (Figure 2 on the previous
page). This method is referred to as condenser splitting. The splitting
of the condensers is done with the addition of a pilot-operated, threeway solenoid valve installed in the discharge line from the compressors
(Figure 3). The splitting of the identical condensers is done in such a
way where only one-half of the condenser is used for winter operation, and
both halves are used for summer operation. The top half of the condenser is
referred to as the summer-winter condenser, and the bottom half of the con-
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controls, and air-side controls like fan cycling or fan variable-speed devices.
This combination of refrigerant-side and air-side controls will minimize the refrigerant charge even more while splitting the condenser. These combinations
will also maintain the correct head pressure for better system efficiencies.
The refrigerant that is trapped in the idle summer condenser during lowambient conditions will flow back into the active system through a bleed
hole in the piston of the three-way valve. This trapped refrigerant will flow
through the piston’s bleed hole, into the valve’s pilot assembly, and back to
the suction header through a small copper line which feeds all parallel compressors (Figure 2).
Another scheme to rid the idle summer condenser of its refrigerant is to have
a dedicated pump-out solenoid valve, which will open when energized and vent
the trapped refrigerant to the common suction header through a capillary tube
restriction. Both the bleed hole in the piston or the capillary tube ensure that the
refrigerant experiences a restriction, and is mostly vaporized before reaching the
common suction header which is under low side (common suction) pressure.
A check valve is located at the summer condenser’s outlet to prevent any
refrigerant from entering it while it is idle and under a low pressure condition.
While not needed for backflow prevention, a check valve is also located at
the outlet of the summer/winter condenser simply to make the pressure drops
equal in both halves of the condenser when both are being used simultaneously in summertime operations.
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B
Helical Oil Separators
ecause refrigerants and refrigeration oils are miscible in one another, there will always be some oil that leaves the compressor with the
refrigerant being circulated. Also, any time flooding or migration
occurs, crankcase oil is sure to be diluted with refrigerant. This will
cause oil foaming at start-ups. Crankcase pressures will build often
forcing oil and refrigerant around the rings of the compressor’s cylinders to be
pumped into the discharge line. Oil separators remove oil from the compressor’s
discharge gas, temporarily store the oil, and then return it to the compressor’s
crankcase. Oil separators are located close to the compressor in the discharge
line. Even though most oil separators are designed to be mounted vertically, there
are some horizontal models available on the market. Oil separators are essential
on low and ultra-low temperature refrigeration systems and on large air conditioning systems up to 150 tons. Most compressor manufacturers require oil
separators on all two-stage compressors. Oil separators can also act as discharge
mufflers to quiet compressor pulsation and vibration noises.
Unusual conditions occur at times to compressors and rapid removal of oil from
the compressor’s crankcase happens. A lot of times these occurrences happen
beyond the control of both the designer and installer. The velocity of the refrigerant flowing through the system should return oil to the compressor’s crankcase.
Even though proper refrigerant system piping designs maintain enough refrigerant velocity to ensure good oil return, sometimes this added pressure drop, which
assists in getting the right refrigerant velocity for oil return, hampers the system’s
efficiencies. A lot of times, a higher than normal pressure drop is intentionally
designed into a system for better oil return. This will cause higher compression
ratios and lower volumetric efficiencies, leading to lower capacities.
A helical oil separator. (Courtesy Ferris State University)
Detrimental Effects of Oil in a System
Oil that gets past the compressor and into the system not only robs the
compressor’s crankcase of vital lubrication, but it coats the walls of the condenser and evaporator. Oil films on the walls of these important heat exchangers will reduce heat transfer. The condenser will not be able to reject heat as
efficiently as it should with an oil film coating its walls. Even though this oil
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film will be hotter and thinner than if it were in the evaporator, system efficiencies will suffer. Head pressures will rise causing higher compression ratios
and lower volumetric efficiencies with lower than normal system capacities.
Oil that coats the walls of the evaporator will decrease heat transfer to the
refrigerant in the evaporator. A film of oil bubbles, which acts as a very good
insulator, will form on the inside of the evaporator. The evaporator will now see
a reduced heat load, which will cause the suction pressure to be lower. Lower
suction pressures cause higher compression ratios and lower volumetric efficiencies. The result is a lower system capacity with much longer running times.
Most metering devices including thermal expansion valves (TXV) and capillary tubes will also experience inefficient performance due to the presence
of oil filming. Capillary tubes may experience wide variation in flow rates.
Usually, reduced refrigerant flow rate with higher head pressures and lower
suction pressures are experienced. TXV remote bulbs may not sense the correct refrigerant temperature at the evaporator outlet, causing improper superheat control. TXV hunting can also occur.
If an oil separator isn’t employed, the compressor often sees slugs of oil
that are returning from the evaporator. The compressor’s pistons can momentarily pump slugs of liquid oil which can build tremendous hydraulic forces
because of the incompressibility of most liquids. Serious compressor valve and
drive gear damage can result.
screen layer occurs. This screen layer serves as an oil stripping and draining
medium. The separated oil now flows downward along the boundary of the
shell through a baffle and into an oil collection area at the bottom of the separator. The specially designed baffle isolates the oil collection and eliminates
oil re-entrainment by preventing turbulence.
Virtually oil-free refrigerant gas exits the separator through an exit screen
just below the lower edge of the helical flighting. A float activated oil return
valve allows the captured oil to return to the compressor’s crankcase or oil
reservoir. When the level of oil gets high enough to raise a float, an oil return needle is opened and the oil is returned to the compressor’s crankcase
through a small return line connected to the compressor’s crankcase.
The pressure difference between the high and low sides of the refrigeration or air conditioning system is the driving force for the oil to travel from
the oil separator to the crankcase. The oil separator is in the high side of the
system, and the compressor’s crankcase is in the low side. This float operated
oil return needle valve is located high enough in the oil sump to allow clean oil
to be automatically returned to the compressor’s crankcase.
Only a small amount of oil is needed to actuate the float mechanism. This
ensures only a small amount of oil is ever absent from the compressor’s crankcase at any given time. When the oil level in the sump of the oil separator
drops to a certain level, the float will force the needle valve closed.
On larger parallel compressor systems, the oil separator gives the oil to
an oil reservoir for temporary storage until a compressor calls for it. The
oil reservoir is usually kept at a pressure at about 20 psi above the common
suction header pressure by a special pressure regulating valve. Many times
there may be a combination oil separator/reservoir. In this case, the oil is
distributed to each compressor’s oil level regulator at a reduced pressure
before entering a compressor’s crankcase.
How Helical Oil Separators Work
Helical oil separators offer 99 to 100 percent efficiency in oil separation
with low pressure drop. Upon entering the oil separator, the refrigerant gas
and oil fog mixture encounter the leading edge of a helical flighting. The gas/
oil mixture is centrifugally forced along the spiral path of the helix, causing
the heavier oil particles to spin to the perimeter where impingement with a
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M
Frost on the Compressor’s Head
any service technicians believe that if there is frost on the
compressor’s head, there is cause for alarm. This is simply not true. Frost is simply frozen dew. Usually on lower
temperature refrigeration applications, the suction line and
part of the compressor’s head will get cold. The part of the
compressor’s head that gets coldest is where the suction vapors enter before
they are compressed. These parts often get cold enough to reach the dew
point of the surrounding air. When the air’s dew point temperature is reached
from coming in contact with the cold suction line and compressor head, water
vapor in the air is cooled to its dew point and will condense on the suction line
and head of the compressor. When this condensed water vapor reaches 32˚F,
it will freeze into frost (Figure 1). So, frost is simply condensed water vapor
or dew, which has reached 32˚ or below.
System Specifications
Consider a low temperature commercial refrigeration application operating
with 7˚ of evaporator superheat and 40˚ of compressor superheat (Figure 2,
page 23). The refrigerated box temperature is 0˚ with an evaporator temperature of –13˚. It is an R-404A system. With an evaporator temperature of –13˚
and the system having 40˚ of compressor superheat, the temperature of the refrigerant coming into the compressor is 27˚ (-13 plus 40). The 27˚ temperature
coming into the compressor is lower than the surrounding air’s dew point,
and it is also lower than the freezing point of water (32˚), so the dew on the
suction line and compressor’s head will form frost. These frost lines are completely normal for this low temperature application refrigeration machine.
Figure 1. Condensed water vapor freezes into frost.
(Courtesy of Ferris State University.)
Compressor Flooding or Slugging?
Because the system has a compressor superheat of 40˚, there is no worry
about whether the compressor is flooding or slugging. In review, flooding is liquid refrigerant coming back to the compressor’s crankcase during a run cycle.
Slugging is liquid refrigerant or oil actually entering the compressor’s cylinders
and/or valve arrangement and being pumped. Again, because the system has
superheat at the compressor of 40˚, flooding and slugging cannot exist.
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In order for slugging or flooding to occur, the compressor would have to
be experiencing no superheat. In other words, the temperature coming into
the compressor would be the same as the evaporator temperature (-13˚). This
would indicate that there was no compressor superheat and liquid refrigerant
was entering the compressor.
The amp meter on the air cooled, semi-hermetic compressor (Figure 1)
is reading 5.87 amps. The rated load amps (RLA) of the air-cooled, semihermetic compressor is 6.5 amps. We are still quite below the RLA of the compressor. However, if liquid was coming back to the compressor, the amp meter
would be above the RLA rating of the compressor. A mixture of high-density
vapors and liquid is hard for the compressor to pass, causing high amp readings. Valve plate damage usually occurs in these situations. Air-cooled, semihermetic compressors bring the refrigerant gas right back to the head of the
compressor and then to the suction valves directly. This is why it is very important to have some superheat to ensure that vapor and not liquid is returning to
the compressor. This is not the case for refrigerant cooled compressors where
suction gases come into the end bell of the compressor and then pass through
the motor windings before entering the valve arrangement (Figure 3, page 24).
In either scenario, whether the system has compressor superheat and doesn’t
have compressor superheat, both the suction line and compressor’s head would
still be frosted. This is why it is of utmost importance for service technicians
to measure superheat at both the evaporator and compressor to make sure the
compressor is protected from slugging and flooding.
Measuring Compressor (Total) Superheat
In review, compressor superheat or total superheat is all of the superheat
in the low side of the refrigeration system. Compressor superheat consists
of evaporator superheat and suction line superheat. A service technician can
Figure 2. Low temperature commercial refrigeration application.
(Figure from Troubleshooting and Servicing Modern Air Conditioning and
Refrigeration Systems by John Tomczyk)
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measure total superheat by placing a thermometer, thermocouple, or thermistor at the compressor inlet and taking the temperature. A pressure reading
will also be needed at this same location.
For example, consider the example below for a R-404A system with a low
side pressure taken at the compressor of 21 psig or –13˚ and a compressor
inlet temperature of 27˚. The pressure gauge reading on the low side of the
system of 21 psig tells the service technician that there is a –13˚ evaporating
temperature. The compressor superheat calculation is as follows:
Compressor inlet temp. — Evaporator temp. = Compressor superheat
27˚F – (-13˚F) = 40˚F
In this example, the compressor superheat is 40˚. It is possible to have a
TXV adjusted to control the proper amount of evaporator superheat at the
coil and still return liquid refrigerant to the compressor at certain low load
conditions. It is recommended that all TXV controlled refrigeration systems
have some compressor superheat to ensure that the compressor does not see
liquid refrigerant (flood or slug) at low evaporator loads. The TXV, however,
should be set to maintain proper superheat for the evaporator. This will ensure that the compressor will always see refrigerant vapor, and not liquid.
Figure 3. Refrigerant cooled semi-hermetic compressor.
(Figure from Troubleshooting and Servicing Modern Air Conditioning and
Refrigeration Systems by John Tomczyk)
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Ice Flake Machine Troubleshooting
M
any ice flake machines employ an auger rotating within an
insulated freezing cylinder or evaporator. The auger, which
is driven and geared down by a gear motor and gear box
to about 8-16 rpm, has cutting edges or flights. The flights
shave ice from the walls of the freezing cylinder (evaporator) which is flooded with water and has refrigerant lines wrapped around its
outer circumference (Figure 1). The refrigerant lines have vaporizing refrigerant in them which will freeze the water that is in close proximity or contact
to the inside of the freezing cylinder.
A water reservoir supplies the right height or level of water to the freezing cylinder. Because water will seek its own level, the water level or height in the water
reservoir will also be the level in the freezing cylinder (Figure 2 on the next page).
Water level in the reservoir is usually controlled by a single float mechanism, or a
dual-float mechanism which controls an electric solenoid valve to bring water to
the reservoir. The water-logged shaved ice is then carried through the water to the
top or head of the freezing cylinder where it is squeezed, extruded, shaped, cut and
eventually falls to an insulated ice storage bin for use (Figure 3 on the next page).
It is of utmost importance that the water level in the reservoir and freezing
cylinder are at the proper levels for the ice flake machine to operate effectively.
What follows are some scenarios for improper water levels in the freezing cylinder, and how they affect other components of the ice flake machine.
Figure 1. A cutting edge, or flight, is shown to the right in this photo of an auger.
(Courtesy of Ferris State University.)
because of water seeking its own level. Since water is the refrigerating load
for an ice flake machine, low water level in the freezing cylinder means low
load on the evaporator. This condition will cause lower than usual evaporator
pressures, thus lower evaporator temperatures.
These low evaporator temperatures will produce harder and colder ice
for the auger to cut. This will put an extra load on the auger, gears, and gear
motor. Often, the gear motor will trip on its overload and sometimes has to
be manually reset. Water reservoirs should have a line indicating the correct
water level for that particular machine.
Low Water Levels
If a float mechanism in the water reservoir is adjusted wrong and the
water level is low in the reservoir, it will also be low in the freezing cylinder
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Figure 2. This schematic shows the relationship of the water level with the freezing cylinder in a flake
ice machine. (Courtesy of Hoshizaki America.)
High Water Levels
If the float mechanism in the water reservoir is adjusted wrong, or the seat in the float
chamber is leaking and the water level is too high, the freezing cylinder will experience high
water levels. This will cause stress on the gear motor from the auger doing more work because
there is more surface area of ice to cut.
Again, the overload may trip on the gear motor. When the gear motor’s overload reset button must be reset often, a service technician should suspect water level problems as a possible
cause. Often, high water levels will cause water to pour over into the ice storage bin and cause
a large melting depression in the stored flaked ice. Also, this new water constantly coming into
the freezing cylinder will impose extra heat load on the evaporator and cause higher than normal evaporating pressures and poor ice quality and quantity. This happens because the higher
quantities of new water will have to be refrigerated to the freezing point to start making ice.
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Figure 3. Water-logged shaved ice is carried through the water
to the top or head of the freezing cylinder where it is squeezed,
extruded, shaped, cut and eventually falls to an insulated ice
storage bin for use. (Courtesy of Ferris State University.)
: HVACR Service and Troubleshooting With The Professor
More Ice Flake Machine Troubleshooting
T
his chapter is part two of our discussion on ice flake machine troubleshooting. The previous chapter examined troubleshooting low and high water levels. This chapter will examine problems associated with water impurities as well as
mechanical problems.
When water is frozen in an evaporator flooded with water, minerals in the
water will often build up on the walls of the evaporator. This mineral buildup
will cause added resistance for the ice cutting auger. Mineral buildup (scale)
is a porous material and is a good insulator to heat transfer. The refrigerant
will now see less heat load from the water in the cylinder and the evaporator
pressure will drop. A drop in evaporator pressure will cause a colder evaporator and harder ice. The cutting auger’s flights now have to cut harder ice
along with minerals that have built up on the evaporator surface. The result
is a loud crunching or squealing noise coming from the evaporator compartment. This added resistance of cutting ice and mineral buildup will also add
extra load on the gear motor. A higher amp draw will be the result.
Figure 1. The ice cutting auger, drive train with gears, and the gear motor are all
connected. (Courtesy of Ferris State University.)
Drive Train (Gears + Shafts)
When the ice-cutting auger is stressed, so is the gear motor and drive train.
The ice-cutting auger, drive train with gears, and the gear motor are all connected (Figure 1). When the gear motor is stressed from cutting hard ice and
minerals, the extra torque generated from the motor will cause excessive heat.
This may cause the gear motor’s overload to open and shut the unit down until
a service person manually resets the overload on the gear motor. Cleaning the
ice flake machine according to the manufacturer’s recommendations with an
approved cleaner, and inspecting the bearings connecting the cutting auger with
the drive train will prevent mineral buildup on the freezing cylinder’s surface
and keep the ice flake machine operating quieter and longer.
Often, grease can leak out of a bearing housing and start a bearing failure.
If a bearing has started to fail, the cutting auger may wobble from the added
clearance in the worn bearing. This wobbling as the auger rotates may cause
the auger to touch the freezing cylinder (evaporator) and scar its surface. If
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scarring of the evaporator surface or auger’s cutting surface has occurred,
one of the components will, for sure, have to be replaced. Always follow the
manufacturer’s recommendation when replacing a cutting auger or freezing
cylinder. It is this gear motor assembly that is more susceptible to failure than
any other part of the ice flake machine.
Remember, as the auger rotates and cuts ice and mineral deposits, the
gear motor and gear assembly senses all of these stresses and strains. It is
for this reason that some manufacturers have manufactured open-type gear
case housing assemblies. This means the gear assembly has a vent and is exposed to the atmosphere, usually with a soft plastic plug holding the gear lube
(grease) from escaping. When excessive heat occurs from gear motor stress,
expanded hot grease can escape through the vent. However, one has to be
careful to keep the vent hole plugged or moisture can enter. This will deteriorate the lubricating effect of the grease, and excessive gear wear will result.
Usually, a regular clicking sound will be heard from the drive train if a gear is
chipped from poor lubrication or too much stress. However, if the auger motor is
starting to fail, a loud, higher pitch noise will be heard. Cleaning the ice flake machine with an approved cleaner and inspecting the bearings connecting the cutting
auger with the drive train will prevent mineral buildup on the freezing cylinder’s
surface and keep the ice flake machine operating quieter and longer.
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T
Restricted TXV Metering Device
his chapter explores how a restricted metering device will
affect system performance and efficiency. The system is a
commercial refrigeration system with a TXV as the metering
device. The refrigerant being used is HFC-134a. Very similar
results will occur if an automatic expansion valve (AXV) is
used. However, because different refrigerant system configurations may
apply when using capillary tubes as metering devices, different system
symptoms may occur. The intent of this chapter is to explore how a partially restricted TXV will affect system performance and efficiency and
what symptoms will occur.
Listed below are ways the metering device (TXV) can become restricted:
• Plugged inlet screen;
• Foreign material in orifice;
• Oil logged from refrigerant flooding the compressor;
• Adjusted too far closed;
• Wax buildup in valve from wrong oil in system;
• Sludge from the byproducts of a compressor burnout;
• Partial TXV orifice freeze-up from excessive moisture in the system; and
• Manufacturer’s defect in the valve.
A system with a restricted metering device has the very same symptoms as a system with a liquid line restriction that occurred after the receiver. This is because the TXV is actually part of the liquid line. A TXV
being restricted will cause the evaporator, compressor, and condenser
to be starved of refrigerant. This will cause low suction pressures, high superheats, low amp draws, and low head pressures.
Also, the symptoms of a restricted TXV system are very similar to a system with a refrigerant undercharge. However, the undercharged system will
have low condenser subcooling levels. Service technicians often confuse an
undercharged system with a restricted metering device.
Adding refrigerant to a system with a restricted metering device will only
raise the condenser subcooling amounts to a level where the head pressure
may elevate. This is caused from a lack of internal volume in the condenser
to hold the added refrigerant. Even the receiver may overfill if too much
refrigerant is added.
Table 1 on the next page shows a system checklist for a system with a restricted metering device. Symptoms can include:
• Somewhat high discharge temperature;
• Low condensing (head) pressure;
• Low condenser split;
• Normal to a bit high condenser subcooling;
• Low evaporator (suction) pressure;
• High superheats;
• Low amp draw; and
• Short cycle on low-pressure control (LPC).
Symptoms
High discharge temperature: Somewhat high discharge temperatures
are caused by the higher superheats from the evaporator being starved of
refrigerant. The compressor is now seeing a lot of sensible heat coming from
the evaporator and suction line, along with its heat of compression and mo-
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tor heat. The compressor will probably overheat from the lack of refrigerant
cooling if it is a refrigerant-cooled compressor.
Low condensing (head) pressures: Since the evaporator and compressor are being starved of refrigerant, so will the condenser because these components are in series with one another. There will be little heat to eject to the
ambient surrounding the condenser. This allows the condenser to operate at a
lower temperature and pressure.
Low condenser splits: Since the condenser is being starved of refrigerant, it can operate at a lower temperature and pressure. This is because it
does not need a large temperature difference between the ambient and the
condensing temperature to reject the small amount of heat it is getting from
the evaporator, suction line, and compressor. This temperature difference is
referred to as the condenser split. If there were large amounts of heat to
reject in the condenser, the condenser would accumulate heat until the condenser split was high enough to reject this large amount of heat. High heat
loads on the condenser mean large condenser splits. Low heat loads on the
condenser mean low condenser splits.
Normal to a bit high condenser subcooling: Most of the refrigerant
will be in the receiver, with some in the condenser. The condenser subcooling
will be normal to a bit high because of this. The refrigerant flow rate will be
low through the system from the restriction. This will cause what refrigerant
that is in the condenser to remain there longer and subcool more. Note that
an undercharge of refrigerant will cause low subcooling.
Low evaporator pressures: Since the evaporator is starved of refrigerant, the compressor will be starving also and will pull itself into a low-pressure
situation. It is the amount and rate of refrigerant vaporizing in the evaporator that keeps the pressure up. A small amount of refrigerant vaporizing will
cause a lower pressure.
Restricted Metering Device
(Measured Values)
Compressor discharge temperature...................................... 200
Condenser outlet temperature................................................ 70
Evaporator outlet temperature............................................... 30
Compressor in temperature.....................................................65
Ambient temperature............................................................. 70
Box temperature................................................................... 30
Compressor volts................................................................. 230
Compressor amps................................................................. low
Low side (evaporating) pressure (psig).................. 1.8 psig (-10˚)
High side (condensing) pressure (psig)................ 104.2 psig (85˚)
(Calculated Values °F)
Condenser split.......................................................................15
Condenser subcooling.............................................................15
Evaporator superheat............................................................ 40
Compressor superheat............................................................75
Table 1. This is a system checklist for a system with a restricted metering device.
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High superheats: High superheats
are caused again from the evaporator
and compressor being starved of refrigerant. With the TXV restricted, the
evaporator will become inactive and
run high superheat. This will cause the
compressor superheat to be high. The
100 percent saturated vapor point in
the evaporator will climb up the evaporator coil causing high superheats.
Low amp draw: High compressor
superheats and low suction pressures
will cause low density vapors to enter
the compressor. Also, the compressor
will be partly starved from the TXV being restricted. These factors will put a
very light load on the compressor causing the amp draw to be low.
Short cycle on the low-pressure
control (LPC): The compressor may
short cycle on the LPC depending on
how severe the restriction in the TXV
is. The low suction pressures may cycle
the compressor off prematurely. After
a short period of time, the evaporator
pressure will slowly rise from the small
amounts of refrigerant in it and the heat
load on it. This will cycle the compressor back on. This short cycling may keep
occurring until the compressor overheats. Short cycling is hard on controls,
capacitors, and motor windings.
A system with a restricted metering device has the very same symptoms as
a system with a liquid line restriction that occurred after the receiver. This
is because the TXV is actually part of the liquid line. (Courtesy of Sporlan
Division, Parker Hannifin Corp.)
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E
Basic Leak Detection Methods
Exposing the Leak
very environmentally conscious service technician should spend
time learning how to check for refrigerant leaks in refrigeration
and/or air conditioning systems. Ozone depletion, global warming, and the increasing price of refrigerants are forcing technicians to become better and more thorough leak detectors. This
chapter will cover some basic methods of leak detection in refrigeration and
air conditioning systems. The next chapter will look at some of the more
advanced methods.
Refrigerant vapor can flow under layers of paint, flux, rust, slag, and pipe
insulation. Often the refrigerant gas may show up quite a long distance from
the leak site. This is why it is important to clean the leak site by removing
loose paint, slag, flux, or rust. Remove any pipe insulation. Oil and grease
must also be removed from the site because they will contaminate the delicate detection tips of electronic detectors.
There are six classifications of leaks.
1.Standing leaks: Standing leaks are leaks that can be detected while
the unit is at rest or off. This includes freezer evaporator coils warmed up by
defrost. Standing leaks, fortunately, are the most common of all leaks.
2.Pressure-dependent leaks: Pressure-dependent leaks are leaks that can
only be detected as the system pressure increases. Nitrogen is used to pressurize
the low sides of systems to around 150 psig, and high sides to 450 psig. Never use
air or pure oxygen. Often, a refrigerant trace gas is introduced into a recovered
and evacuated system along with the nitrogen. The trace gas enables electronic
leak detectors to be used to detect the vicinity of the leak. Refrigerant trace gas
will be covered in more detail later in the article. Pressure-dependent leak testing
should be performed if no leaks are discovered by the standing leak test. Bubbles
or a microfoam solution can also be used to locate pressure-dependent leaks.
Warning: Mixtures of nitrogen and a trace gas of refrigerant, usually of the
system’s refrigerant, can be used as leak test gases because, in these cases, the
trace gas is not used as a refrigerant for cooling. However, a technician cannot
avoid recovering refrigerant by adding nitrogen to a charged system. Before nitrogen is added, the system must be recovered and then evacuated to appropriate
Leak Detection Methods
All sealed systems leak. The leak could be 1 pound per second or as low as
1 ounce every 10 years. Every pressurized system leaks because “flaws” exist
at every joint fitting, seam, or weld. These flaws may be too small to detect with
even the best of leak detection equipment. But given time, vibration, temperature, and environmental stress, these flaws become larger detectable leaks.
It is technically incorrect to state that a unit has no leaks. All equipment
has leaks to some degree. A sealed system which has operated for 20 years
without ever needing a charge is called a “tight system.” The equipment still
has leaks, but not enough leakage to read on a gauge or affect cooling performance. No pressurized machine is perfect.
A leak is not some arbitrary reading on a meter. Gas escapes at different
times and at different rates. In fact, some leaks cannot be detected at the time of
the leak test. Leaks may plug, and then reopen under peculiar conditions. A leak
is a physical path or hole, usually of irregular dimensions. The leak may be the tail
end of a fracture, a speck of dirt on a gasket, or a microgroove between fittings.
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levels. Otherwise, the HCFC, or HFC refrigerant trace gas vented along with the
nitrogen will be considered a refrigerant. This will constitute a violation of the
prohibition on venting. Also, the use of CFC as a trace gas is not permitted.
3.Temperature-dependent leaks: Temperature-dependent leaks are
associated with the heat of expansion. They usually occur from high-temperature ambient air, condenser blockages, or during a defrost period.
4.Vibration-dependent leaks: Vibration-dependent leaks only occur
during unit operation. The mechanical stain of motion, rotation, refrigerant
flow, or valve actuation are all associated with vibration-dependent leaks.
5.Combination dependent leaks: Combination dependent leaks are
flaws that require two or more conditions in order to induce leakage. For example, temperature, vibration, and pressure cause the discharge manifold on
a semi-hermetic compressor to expand and seep gas.
6.Cumulative microleaks: Cumulative microleaks are all the individual
leaks that are too small to detect with standard tools. The total refrigerant loss over many years of operation slightly reduces the initial refrigerant
charge. A system having many fittings, welds, seams, or gasket flanges will
probably have a greater amount of cumulative microleaks.
Figure 1. In leaking systems, oil spots can appear wet and have a fine coating of
dust. (Photo courtesy of Refrigeration Technologies, Anaheim, Calif.)
first quick-check, but is not always reliable for the following reasons:
• Oil is always present at Schrader valves and access ports due to the discharging of refrigerant hoses on the manifold and gauge set. (Figure 2, next
page). Often these parts are falsely blamed as the main point of leakage.
• Oil blotches can originate from motors, pumps, and other sources.
• Oil residue may be the result of a previous leak.
• Oil is not always present at every leak site. It may take months, even years
of unit operation to cause enough oil blow-off to accumulate on the outer side.
• Oil may not be present with micro-leaks.
• Oil may not reach certain leak positions.
• Oil may not be present on new start-ups.
Spotting Refrigerant Oil Residue for Standing Leaks
Successful leak detection is solely dependent on the careful observation
made by the testing technician. Fortunately, all refrigeration systems internally circulate compressor oil with the refrigerant. Oil will blow off with the
leaking refrigerant gas and “oil mark” the general area of leakage. Oil spots
appear wet and have a fine coating of dust (Figure 1). The technician must
determine that the area wetness is oil and not condensate. This can be accomplished by rubbing the area with your fingers and feel for oil slickness.
However, what is the reliability of oil spotting? Oil spotting is the technician’s
Testing for Evaporator Section Leaks
Many leaks that go undetected are in the evaporator coil. This is because
most evaporator sections are contained in cabinets, buttoned-up, or framed
into areas that do not allow easy access. In order to avoid time-consuming
labor to strip off covers, ducting, blower cages, or the unloading of product,
an easy electronic screening method is outlined on the next page.
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3.Calibrate an electronic leak detector to its highest sensitivity.
4.Locate the evaporator drain outlet or downstream drain trap.
5.Position the electronic leak detector probe at the drain opening. Be careful that the leak detector probe does not come into contact with any water.
6.Sniff with the electronic detector for a minimum of 10 minutes or until
a leak is sensed. Recalibrate the device and test again. Two consecutive “positive” tests confirm an evaporator leak. Two consecutive “negative” tests
rules out an evaporator section leak.
Remember, refrigerant gas is heavier than air. Gravity will cause the gas to flow
to the lowest point. If the evaporator section tests positive, the technician should
expose the coil and spray coat all surfaces with a specially formulated bubble/foam
promoter. Bubble/microfoam solutions have been very successful in leak detection
because of their price and effectiveness. Leaks can be easily pinpointed with these
solutions. Often, a mild soap and water solution is used for bubble checking. Research has shown that soap and water does not have the same properties as do the
micro-foam solutions that contain coagulants and wet adhesives. Household detergents often contain chlorides and will pit and corrode brass and iron.
The specially formulated and patented bubble solutions have entered the
market with remarkable results. These new solutions will form a foam “cocoon” when in contact with a leak. All that is required is for the solution to be
applied over the suspected leak area. When a leak is found, bubbles or foam
will tell the technician of its location. The technician must be patient and let
the bubbles stand for at least 10-15 minutes if small leaks are suspected.
Another advantage of bubble testing is that bubbles can be used with nitrogen or refrigerants pressurizing the system. Small, significant leaks of less
than a couple ounces per year can often be found with special formulated microfoam solutions. If the evaporator section tests negative for leaks, continue
on to leak testing the condensing unit.
Figure 2. Oil is always present at Schrader valves and access ports due to the
discharging of refrigerant hoses on the manifold gauge set. (Photo courtesy of
Refrigeration Technologies, Anaheim, Calif.)
1.Turn off all system power including evaporator fan motors.
2.Equalize high- and low-side pressures in the refrigeration or air conditioning system and defrost any frozen evaporator coils. (If the system does not
have any pressure, evacuate to the required levels and then add a refrigerant
trace gas. Nitrogen is then added to generate a practical test pressure). Most
low sides of systems have a working pressure of 150 psig, but always read the
nameplate on the evaporator section for test pressure specifications.
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Testing for Condensing Section Leaks
To test for condensing section leaks:
1.Calibrate an electronic leak detector to its highest sensitivity and place
the probe at the base of the unit, usually under the compressor. The unit
should be fully pressurized.
2.Cover the condensing unit with a cloth tarp or bed sheet to serve as a barrier against any outside air movement and to trap refrigerant gas (Figure 3).
Do not use a plastic material because some plastics may set off some electronic
leak detectors and give a false reading.
3.Monitor for leakage for 10 minutes or until a leak is sensed. Recalibrate and test again. Two consecutive positive tests confirm condensing section leakage. Two consecutive negative tests rule out a detectable leak.
4.Use the electronic leak detector to check for leaks on the bellows of the
pressure controls. Remove the control box cover and place the probe within
the housing. Cover the control tightly with a cloth barrier and monitor for 10
minutes as above.
5.If the results are positive, uncover the equipment and begin spray coating with a microfoam solution. If the results are negative, continue to the suction/liquid line leak test that follows.
Figure 3. In testing for leaks, cover the condensing unit with a cloth tarp or bed sheet
to serve as a barrier against any outside air movement and to trap refrigerant gas.
(Photo courtesy of Refrigeration Technologies, Anaheim, Calif.)
The suction line can be screened by calibrating an electronic leak detector
to its highest sensitivity. Tuck the probe underneath the pipe insulation. Monitor
for 10 minute intervals while the system is at rest and fully pressurized to equalization. It may be necessary to insert the probe at several downstream points.
If a leak is sensed, strip off insulation and apply a bubble/foam promoter
to all surfaces. If no leak was positively screened, test the liquid line.
Suction + Liquid Line Leak Test
The longer the tubing runs are between the evaporator and condensing
unit, the greater is the odds for defects. Count on all possibilities whether
it be a typical sight glass-drier connection leak to a poor solder joint hidden
under pipe insulation.
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T
Advanced Leak Detection
he last chapter introduced the topic
of leak detection and provided details on basic detection methods.
This chapter will look at more advanced methods. You may recall
that the previous chapter outlined various classes
of leaks with standing leaks as the most common.
How to deal with such leaks was covered in that
chapter as the first classification of leaks.
mixture. Even some refrigerants when mixed with
air or oxygen can become explosive under pressure.
Pure oxygen and the oxygen in the air will oxidize
the system’s oil rapidly. In a closed system, pressure
from the oxidizing oil can build up rapidly and may
generate pressures to a point of exploding.
The second step in testing for pressure-dependent leaks is to always conduct proper bubble testing
by thoroughly saturating all surfaces with a microfoam solution. Allow up to 15 minutes reaction time
for the microfoam to expand into a visible white “coPressure-Dependent Leaks
coon” structure (Figure 1 and Figure 2, shown on
The second classification was the pressure-dethe next page). Use an inspection mirror to view any
pendent leaks which can only be detected as the sysundersides and a light source for dark areas.
tem pressure increases. So we will begin with a disThird, starting at the compressor, coat all suscussion of how to test for pressure-dependent leaks. Figure 1. In using a micro-foam solution for leak testing,
allow up to 15 minutes reaction time. (Photo courtesy of
pected surfaces. Continue to coat all suction line
First, you need to pressurize the low side to Refrigeration Technologies, Anaheim, Calif.)
connections back to the evaporator section.
150 psig and the high side to 450 psig using dry
Fourth, spray coat all fittings starting at the discharge line at the compresnitrogen. The equipment rating plate usually states the maximum pressure
sor to the condenser coil. Spray coat all soldered condenser coil U-joints.
permissible. Also, always make sure that valving and other components can
Fifth, from the condenser, continue to spray coat all liquid line connections
take these pressures whether they are original equipment or not. If the high
including the receiver, valves, seams, pressure taps, and any mounting hardside and low side cannot be split by ways of isolation valves, pressurize the
ware. Continue the liquid line search back to the evaporator section.
entire system to about 350 psig if permissible.
Sixth, any control line taps to the sealed system must be spray coated the
Warning: Never use pure oxygen or air to raise the pressure in a refrigeraentire length of their run all the way back to the bellow device.
tion system. Pure air contains about 20 percent oxygen. The pure oxygen and/
Seventh, expose the evaporator section and coat all connections, valves,
or the oxygen in the air can combine with refrigerant oil and cause an explosive
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These metals actually warp when heated, then
contract and seal when heat is removed.
The procedures to deal with that are:
1. Place the unit in operation and raise the
operating temperature by partially blocking the
condenser’s air intake.
Warm water may also be used for system pressurization. Water chillers are usually pressurized
using controlled warm water. When dealing with
chillers, valve off the condenser and evaporator
water circuits. Controlled warm water is now introduced on the evaporator tube bundle. This causes
the rate of vaporization of the refrigeration to increase, causing higher pressures in the evaporator.
One must slowly control the amount of warm
Figure 2. Proper bubble testing for leaks includes
Figure 3. An example of a micro-foam solution
thoroughly saturating all surfaces. (Photo courtesy of
used for leak testing. (Photo courtesy of
water introduced to avoid temperature shock to the
Refrigeration Technologies, Anaheim, Calif.)
Refrigeration Technologies, Anaheim, Calif.)
evaporator. The rupture disc on the evaporator may
open if the pressures are raised too high. There are
and U-joints.
special fittings available from the chiller manufacturer to equalize pressure inside
Notice that the first sequence of searching started with the compressor
and outside of the rupture disc to prevent rupture. Please consult with the chiller
and suction line due to their large surface areas.
manufacturer before attempting to service or leak check any chiller.
The next sequence began with the discharge line, went across the condenser
An electronic leak detector may be used while the system is running. Howto the liquid line connection, and then to the evaporator section. The evaporator
ever, running a system usually causes a lot of fast air currents from fans and
section is the last and least desirable component to pressure test in the field.
motors that may interfere with electronic detection. It helps to cover the unit
with a blanket or sheet to try to collect escaping refrigerant gases. The leakTemperature-Dependent Leaks
ing refrigerant will be easier to pick up with an electronic detector if it can
The third classification of leaks is temperature dependent. All mechanical
collect somewhere, instead of being dissipated by air currents.
connections expand when heated. The connections on refrigeration and air con2.Spray coat all metal connections with a microfoam solution (Figure 3)
ditioning systems are usually of soft metals such as copper, brass, or aluminum.
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one at a time and observe for leakage. Rewet any extremely hot surfaces with
water to keep the fluid from evaporating too quickly.
3.When testing evaporator components, you may induce heat by placing the
unit into defrost.
Vibration-Dependent Leaks
The fourth classification of leaks is vibration dependent. Leaks that only occur while the unit is in operation are the rarest of all leaks. They are cracks that
open and close from physical shaking. However, studies have shown that certain
components and piping on refrigeration units will develop vibration leaks.
An electronic leak detector or a microfoam solution can be used while
the unit is running. Again, drafts have to be minimized when the unit is running for use of an electronic detector. If an electronic detector is used first,
a blanket or sheet should be used to help collect escaping gases and minimize air currents.
If a microfoam solution is used, place the unit in operation and spray coat
the following areas with the solution. Look for large bubbles or foam cocoons
formations. Large bubbles will form on larger leaks (Figure 4) and foam cocoons will form on small leaks.
Below are areas to spray coat:
• All compressor bolts and gasket edges;
• Suction line connection at compressor;
• Suction line connection at evaporator;
• Discharge line connection at compressor;
• Discharge line connection at condenser;
• Vibration eliminators;
• Any joint or fitting on unsupported pipe runs;
• Expansion and solenoid valves;
Figure 4. Large bubbles form on larger leaks. (Courtesy of Refrigeration
Technologies, Anaheim, Calif.)
• Capillary tube connections; and
• Sight glass.
Combination-Dependent Leaks
Dealing with combination-dependent leaks — the fifth classification of
leaks — involves overlapping the procedures already mentioned. At least two,
and usually three, procedures should be merged into one procedure. This type
of testing requires a high order of skills and observation techniques. Each suspected component must be isolated and tested in the following manner:
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Such superfine leak testing is beyond
the normal operations of the service
technician. Microleaks are considered
an acceptable amount of leakage in our
industry at this point in time.
4.Gently add heat to the component. If no leakage, continue on to another
component.
Cumulative Microleaks
The sixth and final classification of leaks discussed over these past two
chapters was a cumulative microleak that is measured using a helium mass
spectrometer. Such superfine leak testing is beyond the normal operations of
the service technician. Microleaks are considered an acceptable amount of
leakage in our industry at this point in time.
1.A valve or fitting is subjected to high pressure.
2.Spray coat the valve or fitting.
3.Tap the component repeatedly with a rubber mallet to induce vibration.
If there’s no leakage, then go to step 4.
Note: The technical information and photographs contained in this chapter
and the previous chapter on leak detection were used with the permission of
Refrigeration Technologies, Anaheim, Calif.
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Checking on Refrigerant Overcharge
T
Refrigerant Overcharge
his chapter will discuss refrigerant overcharge. The check sheet
shown on this page depicts a refrigeration system with an overcharge of refrigerant. The system in this example is a lowtemperature HFC-134a refrigeration unit with a TXV/receiver.
(See the chart at right.)
(Measured Values)
Symptoms
Symptoms can include:
• High discharge temperature
• High condenser subcooling
• High condensing pressures
• Higher condenser splits
• Normal to high evaporator pressures
• Normal superheats
• High compression ratio
High Discharge Temperatures: With an overcharged system, the high
compressor (superheated vapor) discharge temperature of 240˚ is caused from
the high compression ratio. A discharge temperature of 225-250˚ is considered
the maximum discharge temperature in order to prevent system breakdown
from excessive heat. Liquid backed up in the condenser from the overcharge
of refrigerant will flood some of the condenser’s internal volume at its bottom
causing high head pressures. All of the heat being absorbed in the evaporator
and the suction line, along with motor heat and high heat of compression from
the high compression ratio, has to be rejected into a smaller condenser’s internal volume because of the backed up (overcharged) liquid refrigerant.
Compressor Discharge Temperature
240˚
Condenser Outlet Temperature
90˚
Evaporator Outlet Temperature
15˚
Compressor In Temperature
25˚
Ambient Temperature
70˚
Box Temperature
10˚
Compressor Volts
230
Compressor Amps
High
Low Side (Evaporating) Pressure (PSIG)
8.8 (5˚)
High Side (Evaporating) Pressure (PSIG)
172 (120˚)
(Calculated Values ˚F)
41
Condenser Split
50
Condenser Subcooling
30
Evaporator Superheat
20
Compressor Superheat
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pressure would be caused by the decreased mass flow rate through the compressor from high compression ratios causing low volumetric efficiencies. The
evaporator would have a harder time keeping up with the higher heat loads
from the warmer entering-air temperature. The TXV will also have a tendency to overfeed refrigerant to the evaporator on its opening stroke due to
the high head pressures.
Normal Evaporator Superheats: The TXV will try to maintain superheat even at an excessive overcharge. As mentioned above, the TXV may
overfeed slightly during its opening strokes, but then should catch up to itself
if still in its operating pressure ranges.
High Compression Ratios: The condenser flooded with liquid during the
overcharge will run high condensing pressures. This causes high compression
ratios and causes low volumetric efficiencies causing low refrigerant flow rates.
High Condenser Subcooling: Because of the overcharge of refrigerant
in the system, the condenser will have too much liquid backed up at its bottom
causing high subcooling. Remember, any liquid in the condenser lower than the
condensing temperature is considered subcooling. You can measure this at the
condenser outlet with a thermometer or thermocouple. Subtract the condensing out temperature from the condensing temperature to get the amount of
liquid subcooling in the condenser. A forced-air condenser used in refrigeration
should have at least 6-8˚ of liquid subcooling in the condenser. However, subcooling amounts do depend on system piping configurations and liquid line static
and friction pressure drops. Condenser subcooling is an excellent indicator of
the system’s refrigerant charge. The lower the refrigerant charge, the lower the
subcooling. The higher the charge, the higher the subcooling.
High Condensing Pressures: Subcooled liquid backed up in the condenser causes a reduced condenser internal volume and raise condensing
pressures. Now that the condensing pressures are raised, there is more of
a temperature difference between the surrounding ambient and condensing
temperature, causing greater heat flow. This compensates for the reduced
condenser’s internal volume. The system will still reject heat, but at a higher
condensing pressure and temperature.
High Condenser Splits: Because of the higher condensing pressures,
thus higher condensing temperatures, there will be a greater temperature
difference (split) between the ambient and condensing temperature. A dirty
condenser will also give a system high condenser splits, but the condenser
subcooling will not be as high as with an overcharged system.
Normal to High Evaporator Pressures: Since this system has a TXV
metering device, the TXV will still try to maintain its evaporator superheat,
and the evaporator pressure will be normal to slightly high depending on the
amount of overcharge. If the overcharge is excessive, the evaporator’s higher
Overcharged Capillary Tube Systems
If we are dealing with a capillary tube metering device, the same symptoms occur with exception to the evaporator superheat. Remember, capillary
tube systems are critically charged to prevent liquid floodback of refrigerant
to the compressor during low evaporator loads. The higher head pressures of
an overcharged system incorporating a capillary tube as a metering device will
have a tendency to overfeed the evaporator, thus decreasing the superheat.
If the capillary tube system is severely overcharged, liquid can enter the
suction line and get to the suction valves or crankcase. This will cause compressor damage and eventually failure.
Again, it is the system check sheet that will tell the service technician
whether a system is overcharged or not. Service technicians must install pressure gauges and thermistors or some other sort of temperature sensing devices in order to systematically troubleshoot a refrigeration system correctly.
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R
Refrigerant Migration
efrigerant migration is defined as refrigerant, either liquid or
vapor, traveling to the compressor’s suction line or crankcase
during the off cycle. During the off cycle, or especially during a
long shutdown, refrigerant will want to travel, or migrate, to a
place where the pressure is the lowest.
In nature, most fluids travel from a place of higher pressure to a place of
lower pressure. The crankcase usually has a lower pressure than the evaporator because of the oil it contains. Oil has a very low vapor pressure and refrigerant will flow to it whether the refrigerant is in the vapor or liquid form.
In fact, refrigerant oil has such a very low vapor pressure it will not vaporize
even when a 100-micron vacuum is pulled on the refrigeration system.
Some refrigeration oils have a vapor pressure of as low as 10 microns. If
the oil did not have a very low vapor pressure, it would vaporize every time a
low pressure exists in the crankcase, or a vacuum was pulled on it.
If refrigerant migration does occur, and the crankcase is lucky enough to have
a crankcase heater, the vapor will be forced away from the crankcase and end
up in the suction line. This refrigerant may condense in the suction line and cause
slugging in the compressor’s cylinders on start-up. Slugging is liquid refrigerant
or liquid oil actually trying to be compressed in the cylinders of the compressor.
Slugging happens during the compressor’s on-cycle. As we know, liquids cannot
be compressed, and tremendous reversal forces are generated often resulting in
broken parts. Slugging can especially happen if the compressor is located in a cold
ambient outdoor setting. The cold ambient will amplify the lower vapor pressure
area and help condense the refrigerant vapor to liquid. The crankcase heater does
help keep the oil in the crankcase free of refrigerant from refrigerant migration.
Because refrigeration migration can occur with refrigerant vapor, the migration can occur uphill or downhill. Once the refrigerant vapor reaches the crankcase, it will be absorbed and condense in the oil. Refrigerant and oil have a strong
attraction for one another and mix very well. Since liquid refrigerant is heavier
than oil, the liquid refrigerant will be on the bottom of the oil in the crankcase.
On short off cycles, the migrated refrigerant does not have a chance to
settle under the oil, but does still mix with the oil in the crankcase. When the
compressor does turn on, the sudden pressure drop on the crankcase containing liquid refrigerant and oil will cause the refrigerant in the oil to flash to a
vapor. This causes violent foaming in the crankcase.
The oil level in the crankcase will now drop and mechanical parts will be
scored from inadequate lubrication. The crankcase pressure will now rise and
the mixture of refrigerant and oil foam can now be forced through compressor passages and around piston rings and be pumped by the compressor.
Not only does this situation cause loss of oil from the crankcase to the
system, but it can also cause a mild form of slugging in the compressor’s cylinders. High compressor current draw, which will lead to motor overheating
usually, follows. Also, broken or warped valves can occur as a result of overheating and/or slugging.
Solution
The only sure solution in avoiding migration is to get rid of all the refrigerant in the evaporator, suction line, and crankcase before the off-cycle. An automatic pump down system can accomplish this. A thermostat controlling box
temperature is wired in series with a liquid line solenoid. When the box tem-
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Figure 1. Schematic diagram of an automatic pump down system.
(Figure from Troubleshooting and Servicing Modern Air Conditioning and
Refrigeration Systems by John Tomczyk)
perature is satisfied, the thermostat contacts will open. This will de-energize
the liquid line solenoid and a pump down cycle will be initiated. Soon all the
liquid and vapor refrigerant from the solenoid forward through the compressor will be pumped into the high side (condenser and receiver) of the system.
Once the low-side pressure reaches about 10 psig, a low-pressure controller
will interrupt the compressor circuit initiating an off cycle. The system is now
pumped down and migration cannot occur because of lack of refrigerant vapor
Figure 2. Pictorial diagram of an automatic pump down system.
(Figure from Troubleshooting and Servicing Modern Air Conditioning and
Refrigeration Systems by John Tomczyk)
and liquid in the evaporator, suction line, and crankcase. When the box thermostat then calls for cooling, the liquid line solenoid is energized; refrigerant pressure will now travel through the metering device to the low side of the system.
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This pressure will cause the cut-in pressure of the low-pressure control to
close its contacts and bring the compressor to another on-cycle. The cut-in
pressure for the low-pressure control is system and refrigerant dependent. It
has to be high enough to prevent any short cycling of the compressor during an
on-cycle, but low enough to allow the low side pressure to reach it when the
box thermostat initiates an on-cycle. Actual trial and error will allow a service
technician to determine the low-pressure control’s settings.
Figures 1 and 2 (both shown on the previous page) show an automatic pump
down circuit and system in both schematic and pictorial forms respectively. It
is important not to let the low-side pressure get too low before shutting off the
compressor. If the low-side pressure was allowed to drop to 0 psig before the
low-pressure control terminated the cycle every off cycle, damage could occur
to the compressor from lack of refrigerant mass flow rate and high compression
ratios. This severely unloads the compressor and may cause overheating from
loss of the cooling effect on the compressor’s windings. A cutout pressure of
10 psig is low enough to ensure most of the liquid and vapor refrigerant has
been cleared from the evaporator, suction line, and crankcase to prevent refrigerant migration during the off cycle.
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H
Flooding and Slugging
VACR field service terminology is often confusing and misused
even by the most seasoned service veterans. Clarification of
terminology among service technicians is of utmost importance in order to clarify the real problem and efficiently find
the correct remedy. Clear, concise, and accurate communication between service technicians, part suppliers, customers, and the home
shop is rapidly gaining importance as the HVACR field transitions become
more technically oriented.
The previous chapter on refrigerant migration discussed how this issue
can damage the compressor’s mechanical parts. It also covered remedies to
migration using automatic pump-down systems. This chapter will cover flooding and slugging of compressors. Two important service terms that are often
misunderstood and misused by service technicians are “flooding” and “slugging.” Each one will be thoroughly defined and explained as they apply to
refrigeration and air conditioning compressors.
• Defrost clock or heater out (iced coil);
• Dirty or blocked evaporator coil;
• Capillary tube overfeeding;
• Capillary tube system overcharged;
• Expansion bulb loose on evaporator outlet;
• Oversized expansion valve;
• Flooding after hot gas termination;
• Heat pump changeover; and
• Defrost termination.
Since liquid refrigerants are heavier than refrigeration oils, liquid refrigerant returning to the compressor will settle under the oil in the bottom of the
compressor’s crankcase. This liquid refrigerant will gradually be boiled off
from the low pressures in the crankcase. However, since the liquid refrigerant
being boiled off is under the oil in the crankcase, very small oil particles will
be entrained in this vaporization process. The oil level in the crankcase will
now drop and rob mechanical parts of vital lubrication.
Often, refrigerant-cooled semi-hermetic compressors have check valves located on a partition between the crankcase and motor barrel to prevent oil and liquid refrigerant from mixing. Air-cooled semi-hermetic compressors and hermetic
compressors are often more prone to flooding. Suction accumulators can help a
flooding condition, but if the situation is severe, accumulators can also flood.
Crankcase pressures can become excessively high from liquid refrigerant
boiling in the crankcase. These high crankcase pressures can cause refrigerant and entrained oil particles to escape around the rings of the pistons during
its down stroke. Once in the compressor’s cylinders, the refrigerant and oil
Flooding
Flooding is liquid refrigerant entering the compressor’s crankcase while the
compressor is running. Flooding occurs to a compressor only during the on cycle.
Causes could be:
• Wrong TXV setting (no compressor superheat);
• Overcharge;
• Evaporator fan out;
• Low load on evaporator;
• End of cycle (lowest load);
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refrigerant-cooled semi-hermetic compressors. This is because refrigerant is often drawn directly into an air-cooled semi-hermetic compressor’s cylinder without passing through the motor barrel. Slugging can result in broken valves, broken
head gaskets, broken connecting rods, and other major compressor damage.
Refrigerant-cooled semi-hermetic compressors will often draw liquid from the
suction line through hot motor windings in the motor barrel, which will assist in
vaporizing any liquid. Even if liquid refrigerant gets past the motor windings, the
check valve in the partition between the crankcase and the motor barrel will prevent any liquid refrigerant from entering the crankcase. High current draws will
be noticed here from dense refrigerant vapors entering the compressor’s cylinder.
Most hermetic compressor’s suction lines end at the shell of the compressor. If liquid refrigerant is entering the compressor, liquid will fall directly
into the crankcase oil and eventually be flashed. As mentioned earlier, this is
referred to as flooding. This causes oil foaming and excessively high crankcase
pressures. Refrigerant and oil droplets will soon reach the compressor’s cylinder and slugging will soon occur.
Slugging in hermetic compressors can also occur from a migration problem. As mentioned before, foaming oil and refrigerant in the crankcase due
to migration will generate excessive crankcase pressures when the on-cycle
occurs. These oil and refrigerant droplets can now get past piston rings and
other small openings and enter the compressor’s cylinder. The end result is
slugging of refrigerant and oil. Slugging can damage reed valves, piston rods,
bearings, and many more mechanical parts.
will be pumped by the compressor into the discharge line. The compressor is
now pumping oil and refrigerant and robbing the crankcase of lubrication.
Oil in the system and not in the crankcase will coat the inner walls of
the tubing and valves and cause unwanted inefficiencies. Higher than normal
crankcase pressures caused from the higher density refrigerant and oil mixture
being pumped through the compressor’s cylinders will cause high compressor
current draw. This may overheat and even trip the compressor. Broken valves
can also occur from this phenomenon. A telltale sign that a compressor’s
crankcase is being flooded with refrigerant will be a cold, frosted, or sweaty
crankcase. A foaming compressor’s oil sight glass with a low oil level are also
signs of flooding. Higher than normal current draws will also be present.
Slugging
Slugging is liquid refrigerant, or liquid refrigerant and oil, entering the
compressor’s cylinder during an on cycle. Causes could be:
• No compressor superheat;
• Migration (off cycle);
• Bad TXV;
• TXV hunting;
• Low load;
• End of cycle (lowest load);
• Evaporator fan out;
• Iced evaporator coil;
• Defrost timer or heater out;
• Dirty evaporator;
• Capillary tube overfeeding; and
• Overcharge.
Air-cooled semi-hermetic compressors are more prone to slugging liquid than
Conclusion
Clarification and understanding of these two technical terms can help
technicians troubleshoot and remedy even the most complex compressor
breakdowns.
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