HVAC/R Systems
HVAC/R Systems
Service Tips with Fluke Multimeters
and Accessories
Application Note
Getting the job
done right
Servicing and maintaining
refrigeration, air conditioning,
and heat pump systems can be
a tricky business—unless you
have the right tools.
Measurements must be
accurate, even when taken
in changing or harsh environments. Speed and ease-of-use
are important, too. Often a
single-point-in-time measurement doesn’t provide all the
information. What you really
need are measurements over
time—minimum/maximum
values recorded overnight,
for example.
In addition, some troubleshooting techniques require
knowledge of temperature,
pressure, voltage, and current
values in a system, which
means that a single-function
meter won’t do.
And finally, there’s often a
customer waiting in the wings,
so you want to make sure your
job gets done right the first
time, every time.
This application note provides information about refrigeration, air conditioning, heat
pump, and heating applications
and how to tackle some typical
troubleshooting tasks using
Fluke thermometers, digital
multimeters, pressure/vacuum
modules, and Fluke HVAC/R
accessories. Basic refrigeration
and heat pump theory is also
provided solely to illustrate
how digital thermometers,
multimeters, and accessories
can make servicing and maintaining HVAC/R systems
straightforward, fast, and
accurate.
Fluke advantages
Fluke meters are handheld,
professional test tools that
provide many advantages
over other measurement tools.
Among these advantages:
• Rugged construction protects
Fluke meters from damage
due to falls and electrical
overloads.
• Compact designs make Fluke
meters easy to carry and
easy to use.
•
•
•
•
Accuracy and resolution for
measurements you can trust.
Versatility to perform many
types of tests required of the
HVAC/R technician.
Safety standards and ratings
to ensure operator protection.
Service means that if anything goes wrong, you’re
backed up by Fluke’s warranties and rapid turnaround
from Fluke’s own Service
Centers.
Refrigeration Theory
Work Safely
Figure 1. Four IEC 1010 Categories
Testing, repair, and maintenance
of electrical and HVAC/R equipment
should be performed by trained and
experienced service personnel who
are thoroughly knowledgeable
about the equipment and electrical
systems. Dangerous voltages and
currents are present that may
cause serious injury or extensive
equipment damage.
Fluke cannot anticipate all possible precautions that you must take
testing all the different equipment
for which this brochure is applicable. Be certain that all power has
been turned off, locked out, and
tagged in any situation where you
must actually come in contact with
the circuit or equipment. Make sure
that the circuit cannot be turned on
by anyone but you. Always practice
Log Out/Tag Out procedures as
required by OSHA or local
regulating agencies.
Use only well designed and
well maintained equipment to test,
repair, and maintain electrical systems and equipment. Use appropriate safety equipment such as safety
glasses, insulating gloves, flash
suits, hard hats, insulating mats,
etc. when working on electrical
circuits. Make sure that multimeters
used for working on power circuits
contain adequate protection on all
inputs, including fuse protection
on ALL current measurement
input jacks.
Use meters designed and rated
for your job application. Modern
electrical test meters are now rated
2
Fluke Corporation HVAC/R Systems
by Overvoltage Category based
on the risk of high-energy
transients traveling through
the power system.
Each Overvoltage Category (CAT)
corresponds to an electrical environment within the electrical distribution system. CAT III meters are
intended for 3 phase distribution
circuits. This includes polyphase
motors on compressors, three phase
fans, feeders, and single phase
lighting. CAT II meters are intended
for single phase receptacle connected loads. CAT I meters are
intended for electronic equipment
connected to (source) circuits in
which measures are taken to limit
transient overvoltages to an appropriately low level.
Newer Fluke test meters are
CAT III and independently certified
to the highest standards currently
available, meeting or exceeding
the requirements for most HVAC/R
applications. Refer to the Fluke
Bulletin titled, “ABCs of Multimeter
Safety,” for an extended description
of these Overvoltage Installation
ratings and requirements.
This brochure is not intended
to be a substitute for the instruction
manuals shipped with your multimeter, thermometer, probes, or
electrical equipment. Make sure
you read and understand all of the
applicable manuals before using
the application information in this
brochure. Take special notice of
all safety precautions and warnings
in the instruction manuals.
All refrigeration applications
are based on the Second Law
of Thermodynamics which
states that heat flows naturally
from a warmer object to a cooler
object. What this means is that
a refrigeration unit does not
destroy heat, nor does it impart
coolness, rather it extracts heat
from an object or area and
moves it to another place
(outside a room to be cooled,
for example).
At the simplest level, the
heat is extracted by routing cold
refrigerant through the area to
be cooled. The heat is transferred to the refrigerant which
is then quickly taken outside of
the cooled area to dissipate heat.
Two types of heat are commonly discussed in HVAC/R
applications: sensible heat and
latent heat. Sensible heat can
be measured with a thermometer and sensed by touch.
Latent heat on the other
hand is often called hidden
heat because it can’t be directly
measured with a thermometer.
For example, water can exist
both in liquid and solid form
at 32°F (0°C) because of latent
heat. In order to change one
pound of water at 32°F (0°C)
into ice at 32°F (0°C), 144 BTUs
of latent heat must be removed.
Latent heat is also a factor in
changing liquids to gas. In this
case, latent heat must be added
to the liquid before it will
change to gas. In order to
change one pound of water
at 212°F (100°C) into steam
at 212°F (100°C), 970 BTUs
of latent heat must be added.
Evaporation (changing a liquid to a gas) and condensing
(changing a gas to a liquid) are
used in refrigeration systems.
Because it takes latent heat to
change a liquid to a gas, refrigerant evaporating into gas
absorbs more heat than it would
in liquid form. In refrigeration
systems, the refrigerant is allowed to evaporate (boil) within
the evaporator, thereby absorbing heat from the area to be
cooled. During condensing, heat
is released at the condenser to
the surrounding area. Thus, this
process is used to get rid of the
heat that has been carried by
the gas from the evaporator.
Although any liquid that can
easily be changed from liquid
to gas and back to liquid can
be used as a refrigerant, special
refrigerants have been developed that exhibit qualities that
are particularly well suited to
refrigeration. A typical refrigerant evaporates (boils) at a temperature below the freezing
point of water, so it readily
absorbs heat during evaporation
even at low temperatures. It is
also desirable for refrigerants
to be nontoxic, non-explosive,
non-corrosive, nonflammable,
environmentally friendly with
low or minimum ozone depletion potential, and stable in
gas form.
The refrigeration cycle
A basic vapor compression
refrigeration system consists
of four primary components; a
metering device (e.g. a capillary
tube or a thermostatic expansion valve), evaporator, compressor, and condenser. (See
Figure 2.) The basic cooling
process is as follows:
First, liquid refrigerant under
high pressure is forced through
a metering device into a lower
pressure region within the
evaporator where it begins
to change to vapor.
The refrigerant is circulated
through the cooling coils of the
evaporator absorbing heat from
the area surrounding the coils.
As it moves through the evaporator, it steadily changes from
almost all liquid to all vapor.
The vapor (and the heat it carries) continues to move through
the coils to the compressor.
The compressor compresses
the gas to a high pressure. The
compression process simulta-
Liquid receiver
Figure 2. The refrigeration cycle. Based on the principle that heat flows
naturally from warmer areas to cooler areas, the refrigeration cycle consists
of seven stages: the compression of the hot gas, then its cooling, condensing,
subcooling, expansion, evaporation, and superheating.
Metering
device
Expansion
Liquid line
neously raises the temperature
of the gas. The hot gas is then
delivered to the condenser
where it is cooled and dissipates the heat and steadily
converts the gas to a liquid.
A liquid receiver (on thermostatic expansion valve systems)
captures the refrigerant
between the condenser and
the metering device. When
the liquid under high pressure
reaches the metering device,
the cycle starts over.
(See Figure 3.)
In most refrigeration systems,
temperature and pressure provide quick and accurate checks
on system performance. Close
monitoring of temperature and
pressure to verify proper control
and operation can ensure
longer system life and reduce
energy consumption.
Evaporator
Condenser
Liquid
receiver
Heat absorbed
Heat released
Evaporator
Condenser
Evaporating
and superheating
Cooling, condensing
and subcooling
Metering device
Area to be cooled
Hot gas line
Return air
Outside air
Compressor
Suction line
Hot gas line
Compressor
Suction line
Compression
Liquid refrigerant under high pressure
Refrigerant changed to vapor (gas)
Gas compressed to high pressure
Figure 3. The refrigeration system. In a typical refrigeration system,
the compressor sends hot gas to the condenser. Then the condensed liquid
passes through an expansion valve into the evaporator where it evaporates
and collects heat from the area to be cooled. The gaseous refrigerant then
enters the compressor where the compression process raises the pressure
and temperature. From the compressor, the refrigerant is routed back to the
condenser and the cycle repeats.
HVAC/R Systems Fluke Corporation
3
Refrigeration Applications
-20
Figure 5. Pressure-temperature chart.
Fluke Corporation HVAC/R Systems
-10.0
-40
Pressure (kPa)
1390.0
-10
1290.0
0
1190.0
10
-30
Pressure (PSIG)
4
20
990.0
Temperature (°C)
30
1090.0
40
890.0
50
790.0
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Temperature (°F)
Figure 4. Suction line superheat using the temperaturepressure method. Measure the pressure at the suction line
service valve. Find the evaporator boiling temperature from a
temperature-pressure chart using suction line pressure. Subtract
this temperature from the suction line temperature measured by
the Fluke digital thermometer. The difference is superheat.
690.0
Suction line
temperature
Pressure
measurement point
590.0
Service valve
490.0
Suction line
Discharge
(hot gas)
line
390.0
Compressor
commonly referred to as the
saturation temperature. Any
additional temperature increase
is called superheat.
Finding suction line superheat requires two temperatures—the evaporator boiling
temperature at a given pressure
and the temperature of the
refrigerant at the outlet of the
evaporator on the suction line,
commonly referred to as the
superheat temperature/pressure
method.
Note: Boiling temperature is derived from
using a pressure-temperature (PT) chart.
On new refrigerant blends with high
temperature glide, this is called the dew
point temperature.
The best method to determine
superheat using Fluke products
is to use the 80PK-8 Pipe
Clamp Temperature Probe in
conjunction with the PV350
Pressure/Vacuum Module. The
80PK-8 Pipe Clamp allows pipe
temperature measurements
to be made more quickly and
accurately than other methods
because it clamps directly to
the pipe without the need to
add insulation and tape or
velcro as in the case of a bead
thermocouple. The PV350
allows accurate and quick
pressure measurements.
When measuring for superheat, allow the system to run
long enough for temperatures
and pressures to stabilize while
verifying normal airflow across
the evaporator. Using the
Superheat and its
80PK-8 Pipe Clamp, find the
measurement
suction line temperature by
clamping the probe around a
In the system’s evaporator,
bare section of the pipe at the
conversion of liquid to vapor
outlet of the evaporator. Pipe
involves adding heat to the
liquid at its boiling temperature, temperature can be read at the
inlet of the compressor on the
suction line if the pipe is less
than 15' from the evaporator
and there is a minimum pressure drop between the two
points. (See Figure 4.) Best
results are obtained when the
pipe is free of oxides or other
foreign material. Next, attach
the PV350 to the suction line
service valve (or refrigerant
service port on your manifold
gauge set). Make a note of the
pipe temperature and pressure.
290.0
A common failure of refrigeration systems is the loss of refrigerant over long periods of
time due to a small leak in the
system. Whenever a system has
been opened and reassembled
it must be checked for leaks.
90.0
Refrigerant leak detection
Additionally, federal law established by the U.S. EPA is requiring systems with predetermined leaks to be repaired
by certified technicians upon
detecting a loss of refrigerant
charge. A pressure test using
refrigerant or an inert gas
allows you to determine if a
leak exists, without examining
every inch of the system.
With proper care, dry nitrogen and a minimum amount
of R-22 as a trace gas may be
used safely when pressure
testing for leaks. The pressure
in the nitrogen cylinder can
reach 2000 psig when full, so
a pressure-reducing device that
has a pressure regulator and a
pressure relief valve must be
used.
Connect the PV350 Pressure/
Vacuum Module and a manifold
gauge set to the system to be
pressurized. After pressurizing
the system, observe the reading
on the digital meter to see if the
pressure holds or if it leaks off.
If a leak is detected, then standard leak detection methods
such as soap suds or electronic
detectors may be employed.
The advantage of using a solid
state pressure gauge and digital
meter is that a leak which may
take hours to detect using only
manifold gauges can be
detected almost immediately,
saving precious time on the job.
190.0
Often, measuring temperatures or pressures at key points
in a system can pinpoint trouble
spots. In addition, basic electrical measurements are required
to verify the proper operation
of the various electrical components such as the compressor
motor. Examples of such
measurements follow.
Subcooling and
its measurement
In the system’s condenser,
conversion of vapor to liquid
involves removing heat from
the refrigerant at its saturation
condensing temperature. Any
additional temperature decrease
is called subcooling. Finding
liquid line subcooling requires
two temperatures—the condensing temperature at a given
pressure and the temperature
of the refrigerant at the outlet
of the condenser on the liquid
line. The liquid line temperature
involves measuring the surface
temperature of the pipe at the
outlet of the condenser. (See
Figure 6.)
Using superheat
to troubleshoot
Convert the liquid line pressure
to temperature using a PT chart
for the refrigerant type being
used. The difference of the two
temperatures is the subcooling
value.
The superheat value can indicate various system problems,
including a clogged filter drier,
undercharge, overcharge, faulty
metering device, or improper
Trouble diagnosis using
superheat and subcooling airflow. Suction line superheat
is a good place to start diagnoData from superheat and
sis because a low reading sugsubcooling measurements can
gests that liquid refrigerant may
be useful for determining varibe reaching the compressor. In
ous conditions within the sysnormal operation, the refrigertem including amount of charge, ant entering the compressor is
expansion valve superheat,
sufficiently superheated above
efficiency of the condenser,
the evaporator boiling temperaevaporator, and compressor.
ture to ensure the compressor
Before making conclusions
draws only vapor and no liquid
from the measured data, it is
refrigerant.
important to check external
A low or zero superheat
conditions that influence system reading indicates that the
performance. In particular,
refrigerant did not pick up
verify proper air flow in cubic
enough heat in the evaporator
feet per minute (CFM) across coil to completely boil into a vapor.
surfaces and line voltage to
Liquid refrigerant drawn into
the compressor motor and
the compressor typically causes
associated electrical loads.
slugging, which can damage
Liquid receiver
Liquid line
Service
port
Condenser
This pressure reading will be
that of the boiling refrigerant
inside the evaporator assuming
no abnormal restrictions in the
suction line. Using this pressure
value, find the evaporator boiling temperature from a PT chart
for the refrigerant type being
used. (See Figure 5.) Subtract
the boiling temperature from
the suction line temperature
to find the superheat.
The suction line temperature
may also be taken by attaching
a bead thermocouple to the
suction line. Be careful to
insulate the thermocouple and
use heat conducting compound
to minimize errors due to heat
loss to ambient air.
Measure
temperature
here
Measure
pressure
here
Note: Condensing temperature is derived
from using the PT chart. On new refrigerant
blends with high temperature glide, this is
called the bubble point temperature.
To measure subcooling with an
80PK-8 Pipe Clamp, allow the
system to run long enough for
temperatures and pressures to
stabilize. Verify normal airflow
and then find the liquid line
temperature by clamping the
80PK-8 around the liquid line.
Attach the PV350 to a service
port on the liquid line (or discharge line at the compressor if
a liquid line valve is not available). Make a note of the liquid
line temperature and pressure.
TRUE RMS MULTIMETER
79
Outside
air
RANGE
40
HOLD
40
V
Compressor
RANGE
CAL
Hz 20kHz
V 1kHz
V
Hz 20kHz
V 1kHz
mV
Hz
40
V
40
V
A
OFF
40
mA
Hot gas line
HOLD
CAL
mV
Hz
TRUE RMS MULTIMETER
79
V
A
OFF
40
mA
600V CAT
1000V CAT
10A
FUSED
COM
V
600V CAT
1000V CAT
10A
FUSED
COM
Suction line
Figure 6. Subcooling. After verifying normal airflow, place the 80PK-8 Pipe Clamp
on the liquid line. Note the temperature. Then attach the PV350 Pressure/Vacuum
Module to a port on the discharge line and measure the liquid line pressure.
Determine the condensing temperature by using the temperature-pressure chart for
the refrigerant type used. The difference in temperature is the subcooling value.
HVAC/R Systems Fluke Corporation
5
Refrigeration Applications
the compressor valves and/or
mechanical components. Additionally, liquid refrigerant in
the compressor, when mixed
with oil, reduces lubrication
and increases wear, causing
premature failure.
On the other hand, if the
superheat reading is excessive,
it indicates that the refrigerant
has picked up more heat than
normal, or that the evaporator is
short of refrigerant. Possibilities
include a metering device that
is underfeeding, improperly
adjusted, or simply broken.
Additional problems with high
superheat could indicate a system undercharge, refrigerant
restriction, or excessive heat
loads upon the evaporator.
Testing for noncondensible gases
within refrigerant
recovery cylinders
Next, determine if the refrigerant is within the proper range
as indicated on the PT chart. If
the measured refrigerant pressure is lower than indicated on
Since the discovery of the ozone the PT chart, it does not have
hole over Antarctica, the Federal non-condensibles. If the measured refrigerant pressure is
Clean Air Act has established
greater than the limit shown
legislation that mandates the
on the PT chart, then there
recovery of refrigerants on all
are noncondensibles residing
air conditioning equipment,
within the cylinder. At this
either stationary or motor
point, the cylinder contents
vehicles. During the recovery
must be transferred into a U.L.
process, the service technician
approved recovery/recycling
must properly handle and process the refrigerant prior to any machine and properly treated
as per manufacturer's instrucreuse in the refrigeration system. This process may be either tions to separate the noncondensible gases from the
a simple recovery of the refrigrefrigerant.
erant, extended recycle proceRepeat this process until the
dures, or shipping the refrigerant to a reclaim site. Regardless refrigerant cylinder pressure is
Using subcooling
of which process the technician within the acceptable pressure
as noted on the PT chart.
chooses, they must determine
to troubleshoot
if the refrigerant cylinder has
An improper subcooling value
Troubleshooting
been contaminated with noncan indicate various system
condensible by-products (such
compressor discharge
problems, including overcharge, as atmospheric air) prior to
line temperatures
undercharge, liquid line restric- recharging the system with
tion, or insufficient condenser
Use the 80PK-8 Pipe Clamp
the used refrigerant.
airflow (or water flow when
Testing for non-condensibles to measure the discharge line
using water cooled condensers). within the refrigerant cylinder
temperature at the discharge
For example, insufficient or
is a simple process. The instru- of the compressor. High
zero subcooling indicates that
temperatures above 275-300°F
ments you will need are the
the refrigerant did not lose the
(135-148°C) will slowly destroy
Fluke PV350 Pressure/Vacuum
normal amount of heat in its
lubricant qualities and perforModule, the 80PK-3A Surface
travel through the condenser.
mance of the compressor. These
Probe Thermocouple, and
Possible troubles include
high temperature conditions
a digital multimeter with
insufficient airflow over the
can be caused by high cona temperature input.
condenser, the metering device
densing temperatures/presHere’s how the test process
stuck too far open, overfeeding, works. Allow the refrigerant
sures, insufficient refrigerant
or misadjusted, or the system
charge, non-condensibles
cylinder to cool down to ambiis undercharged.
within the system, high
ent temperature, preferably in
Excessive subcooling means
a cool shaded area. Connect the superheat from the evaporator,
the refrigerant was cooled more PV350 directly to the refrigerant restricted suction line filters,
than normal. Possible explana- cylinder using a short refrigeror low suction pressure.
tions include an overcharged
These conditions cause the
ant hose with a 1/4" female
system, the metering device is
flare fitting. Attach the electrical compressor to have a higher
restricted, misadjusted (undercompression ratio, work
connections of the module to
feeding), or faulty head pressure your digital multimeter and
harder, generate hotter internal
control during low ambient
hermetic motor windings, and
record the pressure.
conditions.
prematurely creates compressor
Use the 80PK-3A Surface
wear, fatigue and failure.
Probe to measure the temperature of the refrigerant cylinder.
Using your standard PT chart for
the refrigerant, convert the temperature of the tank into its
associated pressure.
Note: On refrigerant blends with a high glide,
refer to the bubble point (liquid) section of the
PT chart.
6
Fluke Corporation HVAC/R Systems
Temperature survey
The Fluke Model 52 Digital
Thermometer allows you to
A temperature survey is a
record minimum and maximum
critical part of the service
temperatures over extended
technician’s job. A quick check
periods of time. To record overof a system’s components not
night values, just select T1, T2
only helps to diagnose troubles
or T1-T2 as the input and push
Note: IR instruments read best when
but also allows you to anticipate measuring an object with a dull (not shiny)
the RECORD button. The therfailures by regular monitoring
surface. If the surface is shiny, dull it with
mometer immediately starts
either black markers, non-gloss paint,
of critical temperatures.
recording the minimum and
masking tape, electrical tape, etc.
(See Figure 7.)
maximum values. Temperature
Use the 80T-IR Infrared
values can be viewed at any
Recording
a
Temperature Probe to do
time by pressing the view buttemperature
overnight
a quick survey of:
ton (recording still continues).
1. Compressor head
If the HOLD button is pushed,
To check refrigeration system
temperatures
the recorded MIN/MAX values
performance, it is often useful
are saved and recording stops.
to record temperatures in the
2. Compressor oil sump
The data is saved until the user
refrigerated space. This allows
temperatures
selects a different input or turns
you to detect problems that
3. Evaporator coil and suction
may go unnoticed with a single off the 52. The Fluke 16 can
line temperatures
also measure MIN/MAX of a
system check.
4. Discharge line temperatures
For instance, in a refrigerated single temperature plus the
benefit of a 100-hour relative
space it is important to ensure
5. Condenser coil and liquid
that temperature variations are time stamp to know when the
line temperatures
MIN/MAX occurred.
minimized. Temperature varia6. Fan motor temperatures
tions may result from changes
With the 80T-IR you can
in load or ambient conditions
Motor compressor
quickly survey a refrigeration
that occur over periods of time, performance test
system by scanning the
so constant monitoring is called
To test small hermetic and
temperatures of various
for. By recording minimum
semi-hermetic compressors
components. While this is often and maximum temperatures
used for medium and low temdone by touching each of the
in key locations over a period
components, a non-contact
of time you can be sure that air perature applications, the following method can be used to
infrared probe is often faster.
circulation and refrigeration
test for internal valve leakage:
capacity meets the application
Attach the PV350 to a DMM and
requirements.
put the PV350 function switch
to cm/in Hg. Connect the PV350
at the suction line service port.
Close the compressor off from
Metering
Liquid receiver
80T-IR
device (TXV)
the low side of system by front
Infrared temperature
5
seating the suction service
probe
valve. Run the compressor for
two minutes. Turn off the compressor and observe the reading. The compressor should
have pulled down to at least
5
16" (410 mm) of Hg. If the
vacuum reading starts weakening toward 10” (254 mm) of Hg
3
vacuum, the discharge valves of
the compressor may be leaking
6
and will probably need to be
6
replaced. If the compressor
doesn’t pull a vacuum below
1
Outside
Return
16" Hg, the suction valves are
air
air
weakening and may need to be
By keeping careful records it is
possible to detect trends that
indicate impending failure. This
allows you to keep the system
in top condition and avoid
costly failures.
R
T-I
E
OB
Y
PR
AN
LE
RM
UP
CO IN GE
MO
ER MADE
80
D
TH
RE
RA
Condenser
Evaporator
INF
4
Discharge
line
3
2
Compressor
Suction
line
Figure 7. Temperature survey. Regularly monitor temperatures at key
locations to anticipate component failure.
HVAC/R Systems Fluke Corporation
7
Refrigeration Applications
3. Check running current. The
Here’s some simple procedures:
readings should not exceed
1. Compressor bearings can fail
manufacturers full load rated
or lock up due to poor piping
amps during heavy load peripractices, which causes oil
ods. Low amps are normal
logging in the system and
during low load conditions.
Caution: Whenever replacing a compressor
results in insufficient oil
with faulty valves, be sure to diagnose the
Excessive current may be due
return to the compressor.
complete refrigeration system before and after
to a shorted or grounded
If the bearings don’t lock up
a new compressor is installed to avoid
windings, a bad capacitor,
and continue to wear during
repeated compressor failures.
a faulty start relay, or an
these conditions, the rotor
indication of excessive
will lower into the stator
Troubleshooting
bearing fatigue.
housing, shorting out the
compressor motor faults
Caution: When doing electrical
windings. To diagnose this
measurements on compressors with
The Fluke Model 30 Clamp
problem, measure the cominternal thermal motor protection devices
Meter is designed to accurately
pressor amps. They should
that have been running extremely hot, be
measure both ac voltage and ac
not exceed manufacturers full
sure to give the compressor time to cool
current. A big advantage of this
down prior to the electrical test. This will
load ratings. Worn bearings
allow the device to reset to its normal
meter is its built-in current
will cause higher than norposition.
clamp. This allows current to be
mal amps. Inspect the oil
measured without breaking into
level via the compressor
Troubleshooting
the electrical circuit.
sightglass. If there is no
compressor motor failures
A compressor failure is often
sightglass, use your Fluke 16
caused by an electrical fault.
caused by refrigeration
and 80T-IR Temperature
To check the compressor for
system problems
Probe to measure the sump
electrical problems, remove
of the compressor housing.
Occasionally, defective comthe electrical terminal cover
The oil level can be detected
pressors
with
electrical
winding
and check the following
with the temperature probe.
failures are condemned premaexternal connections.
The sump temperature will
turely by the service technician
be different on the compres1. Check line voltage at the load as having been caused by an
sor housing at the oil level.
center with the compressor
electrical system problem.
off. Low line voltage causes
Caution: Whenever an oil problem exists
However, compressor electrical
due to poor piping practices, the correct
the motor to draw more curproblems are often caused by
remedy is to fix the piping, not to
rent than normal and may
mechanical system failure or
continue to add more oil to the system.
result in overheating and
inferior installation and service
2.
High discharge temperatures
premature failure. Line voltpractices. These problems
are caused by high head
age that is too high will
include poor piping practices
pressures or high superheat.
cause excessive inrush curresulting in oil not returning to
The compressor discharge
rent at motor start, again
the compressor, high discharge
line can be measured quickly
leading to premature failure.
temperatures creating acids in
using the 80T-IR on a dull
2. Check line voltage at the
the oil, insufficient air flows
section of pipe. Measure the
motor terminals with comacross the evaporator and
discharge pressure using the
pressor running. The voltage condenser coils, extremely low
PV350. Convert the refrigershould be within 10% of the
suction pressures, and liquid
ant pressure to temperature
motor rating.
refrigerant flooding back into
and compare it to the ambithe compressor.
ent air temperature. If there
Diagnosing these refrigerais a temperature difference
tion system problems and
greater than 20-30°F
avoiding compressor failure can
(11-17°C) temperature
be done effectively using the
difference, there is either
Fluke 16 DMM, Model 30 Clamp
noncondensible gases in the
Meter, Model 52 Digital Thersystem or restricted air flow
mometer, 80PK-8 Pipe Clamp,
across the condenser.
80T-IR Infrared Temperature
Note: Temperature differences will vary
Probe, and PV350 Pressure/
due to original manufacturer’s design and
Vacuum Module.
efficiencies.
replaced. If the compressor is
welded or hermetically sealed
and these conditions exist, a
new compressor is the only
possible remedy.
8
Fluke Corporation HVAC/R Systems
3. Insufficient air flows across
the evaporator are easily
checked by using the Fluke
52 Digital Thermometer.
Place a bead thermocouple
on the discharge side of the
coil and on the return side of
the coil. On air conditioning
units, expect about 18-22°F
∆T (10-12°C) and on
refrigeration units about
10-15°F (5-8.5°C) temperature difference.
Note: Temperature differences may vary
depending upon initial design and
humidity requirements.
4. Extremely low suction pressures can be checked using
the PV350. Install it at the
compressor and record your
suction pressure. Convert the
refrigerant pressure to
temperature using the
corresponding PT chart.
Measure the return air
temperature before the
evaporator. Compare the
refrigerant temperature to the
desired evaporator return air
temperature. On air conditioning units, expect about
35-40°F (19-22°C) temperature difference and refrigeration units expect about
10-20°F (5-11°C) temperature
difference.
LOAD
5. Liquid refrigerant flooding
back to the compressor can
be checked by determining
the superheat using the
PV350 and the 80PK-8 Pipe
Clamp. Check suction pressure and convert the refrigerant pressure to temperature,
using your pressure temperature chart. Measure the suction line pipe temperature.
Compare the two temperatures. If there is no temperature difference, then you are
bringing back liquid to the
compressor. If there is a
temperature difference
between 10-20°F (5-11°C),
then you have normal
superheat and you are
not slugging the compressor
with unwanted liquid.
Checking for voltage
imbalance in a threephase compressor motor
(See Figure 8.) Voltage imbalance in three-phase motors is a
problem because it causes high
currents in the motor windings.
These higher currents generate
additional heat that degrades
winding insulation. A 10°F (5°C)
rise in motor temperature can
reduce motor life by half. Voltage imbalance is usually caused
by adding single phase loads
on the same circuit used by the
compressor, although sometimes component failure is
the culprit.
Voltage imbalance for three
phase motors should not
exceed 1%. To calculate voltage
imbalance, use this formula:
% Voltage Imbalance =
87
Measure
voltage
TRUE RMS MULTIMETER
AUTO
AC
push
mVA
Load
off
MIN MAX
RANGE
87
HOLD
TRUE RMS MULTIMETER
AUTO
REL
41/2 DIGITS
REL
AC
Hz
mVA
PEAK MIN MAX
1 Second
mV
mA
A
V
MIN MAX
V
RANGE
HOLD
100 * (Maximum Deviation From Average)
Average Voltage
For example, given voltages of
449, 470, and 462, the average
voltage is 460. The maximum
deviation from the average in
this example would be 11 volts.
The percent imbalance is:
100 x 11 / 460 = 2.39%.
Note that in this example, you
would have a voltage imbalance
problem.
Today’s motors are often
closely matched to the load
requirements and have little
reserve power. Therefore, you
should periodically check motor
supply voltages to ensure long
motor life and reliable service.
A
REL
41/2 DIGITS
Hz
PEAK MIN MAX
1 Second
OFF
mV
mA
A
V
V
LOAD
Load
on
A
OFF
87
TRUE RMS MULTIMETER
AUTO
AC
mVA
Voltage
drop
MIN MAX
RANGE
REL
41/2 DIGITS
HOLD
Hz
PEAK MIN MAX
1 Second
mV
V
V
OFF
mA
A
A
Figure 8. Measuring voltage drop in branch circuits.
Use the Fluke 80 Series DMMs and the Relative mode to
measure voltage drop. First turn off all loads on the
branch circuit. Then measure the voltage at the most
distant outlet on the circuit. Press the REL ∆ mode button
on the DMM while measuring the no-load voltage. The
displayed reading will be stored, and the display will
read zero. Next, turn on all the loads and measure the
voltage again at the same outlet. The voltage drop
(difference between the no-load and the full-load
voltages) will be displayed.
HVAC/R Systems Fluke Corporation
9
Refrigeration Applications
measures up to 10,000 microfarads. This easily allows measurement of large electrolytic
capacitors found on ac motors.
(See Figure 9.) Current should
(See Figure 10.) Some motors
As an added precaution, the
be measured to ensure that the use capacitors in the starting
Model 16 automatically discontinuous load rating on the
circuit to provide additional
charges the capacitor if residual
motor’s nameplate is not
torque to start the compressor.
voltage is present before
exceeded and that all three
This capacitor is removed from
making the measurement.
phases are balanced. If the
the circuit after the motor has
To measure capacitance, first
measured load current exceeds been started. In addition, some disconnect the capacitor (and
the nameplate rating or the
motors have a capacitor
bleed resistor, if installed). Then
current is unbalanced, the life
attached to the “run” winding.
discharge the capacitor using a
of the compressor motor will be It is used to improve the effi20 kΩ 2W resistor. Do not short
reduced due to higher operating ciency (power factor) of the
the terminals as this may damtemperatures. Unbalanced curmotor. This capacitor has a
age the capacitor. Put the meter
rent may be caused by voltage
lower value than the start
in capacitance mode and perimbalance between phases, a
capacitor; thus the run and
form the measurement. Read
shorted motor winding, or a
the start capacitors are not
the microfarads directly from
high resistance connection.
interchangeable.
the meter and compare the
To calculate current imbalIf a capacitor shorts out, the
results to the “mfd” rating
ance, use the same formula as
motor windings may burn out.
stamped on the side of the
for voltage imbalance but
Open capacitors or capacitors
capacitor. Your results should
substitute current in amps.
that have changed value may
be within the “mfd” range of
Maximum current imbalance
result in poor starting or other
the manufacturer’s specifications.
If upon completion of the
for three-phase motors is
improper operation. The capacitypically 10%.
tance function of the Fluke 16
these procedures, you determine you have a faulty capacitor, begin to troubleshoot the
electrical system using your
Fluke 16 for possible shorts or
faulty circuits which may have
T3
caused premature capacitor
failure. Capacitors don’t usually
Check current
Checking for current
imbalance in a threephase compressor motor
T1
Motor side
T2
Motor capacitor
measurements
(on single-phase motors)
44
0A
under load
LD
20
T2 A2 35A
20
0
40
0A
HO
0A
T1 A1 30A
ER
0V
M
T3 A3 30A
A3
A2
Supply side
CO
A1
M
60
0V
V
O
FF
60
LA
C
30
30
20
0V
ET
PM
Motor side
T1
T2
T3
Roll phases and check
current again
Imbalance
caused by supply
Imbalance
caused by motor
T1 A3 30A
T1 A3 30A
T2 A1 30A
T2 A1 35A
T3 A2 35A
T3 A2 30A
A1
A2
A3
Supply side
Figure 9. Locating the source of current imbalance—motor or supply.
Use the Fluke Model 30 to check for current imbalance on each of the
phases while the motor is running under load. If the current in the phases
is unbalanced you can determine if the unbalance is caused by the motor
or supply by interchanging or rotating the phases. First, measure the
current in the phase conductors while the motor is under load, and note
which phase has the highest current. Next, connect supply phase A to
motor terminal T2, phase B to terminal T3, and phase C to terminal T1,
and measure the phase current again. Note: All three phases must be
rotated, or the motor will run in reverse. If the same supply phase still has
the highest current as before the reconnect, the imbalance is caused by
the supply. If the highest current is now carried by another supply phase,
the imbalance could be the result of a shorted winding in the motor.
10
Fluke Corporation HVAC/R Systems
Figure 10. Troubleshooting capacitors. The capacitance function
of the Fluke 16 measures to 9999 µF. This allows measurements of large
electrolytic capacitors found on ac motors. To prevent measurement errors,
the meter’s discharge mode discharges the capacitor if residual voltage is
present. The meter displays “dISC” while discharging the capacitor.
fail in the field under normal
working conditions, unless they
have been subjected to excess
heat conditions or other electrical device failure.
Finally, replace the faulty
capacitor with an exact match.
mine if a fault has occurred.
Maintenance records or measurement of other known good
components can be used for
comparison during troubleshooting.
On single phase motors,
check Start winding, Run windNote: Always remember to analyze each
electrical system cautiously, working safely,
ing, Start to Run winding. The
to cure the problem prior to installing
ohms reading between the
a new capacitor in your system to avoid
three windings will provide
repeat failures.
three different readings as
follows: the highest resistance
Determine the condition
is found between the Start and
of motor windings
Run windings, the least resis(See Figure 11.) Some compres- tance between the Common
sor failures are due to shorts,
and Run windings, and the
grounds or opens in the windmiddle amount of resistance is
ings. While a motor circuit tester between the Common and Run
may be necessary for a comwindings.
plete checkout, these failures
On 3φ motors, check phase
are easily detected with a
to phase, and phase to ground.
handheld meter such as the
The phase to phase ohm readFluke 79.
ings should be equal between
The Fluke 79 works well for
phases, with no continuity from
checking motor windings and
any phase to ground.
relays for shorts, grounds, and
opens. First disconnect the
Analog gauge calibration
system wiring from the compressor; this includes the relay, (See Figure 12.) Analog manicapacitors, and overload protec- fold gauges often become inaction. Then check the resistance curate and out of calibration
of the motor windings to deter- through rough handling and
normal wear. The PV350 and a
Fluke DMM combination when
used with a known pressure
reference source is significantly
more accurate than, and can be
used to verify, an analog gauge.
The best reference pressure
source is to use a new, uncontaminated standard refrigeration cylinder at a known
temperature and pressure.
First connect the PV350 to
the digital meter and put the
function switch in the proper
function for verification. If a
manifold gauge is being verified, attach the PV350 to the
center port of manifold gauge
set. Apply pressure to the analog gauge from the refrigerant
cylinder. Measure the cylinder
temperature using the Fluke
80PK-3A and then reference
the temperature to a PT chart
for the expected pressure. View
the display on the digital meter.
Compare the reading from the
PV350 to the pressure/temperature of the refrigerant. Adjust
the analog gauge calibration
screw as necessary to match
the two pressures.
R
S
C
TRUE RMS MULTIMETER
79
RANGE
40
HOLD
CAL
V
Hz 20kHz
V 1kHz
mV
Hz
40
V
A
OFF
40
mA
V
600V CAT
1000V CAT
Winding
C-R
Resistance
2Ω
10A
FUSED
COM
Figure 11. Checking motor windings. Disconnect supply wiring from
the compressor. Then check the motor windings to determine if a fault has
occurred. Maintenance records or known good components can be used
for comparison.
Figure 12. Analog gauge calibration. If a manifold gauge set is being verified,
attach the PV350 to the center port of the manifold gauge set. Apply pressure or
vacuum to the analog gauge. Adjust the analog gauge calibration screw or bezel
as necessary.
HVAC/R Systems Fluke Corporation
11
Heat Pump Theory
Heat pumps
(See Figure 13.) Heat pumps are
a variation of a refrigeration
system. They are unique in that
they have the capability of operating as both a heating and
cooling system. A typical air-toair system includes two coils
labeled “indoor coil” and “outdoor coil.” Each coil has its own
expansion device. A reversing
valve steers the direction of the
refrigerant flow, making one
coil the condenser and the
other the evaporator. When the
thermostat calls for heat, the
controls position the reversing
valve to select the indoor coil
as the condenser and the outdoor coil as the evaporator.
As the refrigerant evaporates
in the outdoor coil it picks up
heat from the outside air.
The compressor raises the
temperature and pressure of the
refrigerant and delivers it to the
indoor coil where it gives up
heat to the indoor air. In the
cooling mode, the coils reverse
roles and heat is removed from
the indoor air and transferred
to the outside air.
Heat pumps are most efficient as heating systems when
they are installed in moderate
climates that have average outside air temperatures during
winter months above 32°F
(0°C). When the temperature
falls below freezing or the balance point of the heat pump
system, the system will require
an auxiliary heat source. This
auxiliary heat or supplemental
heat is normally provided as
electric resistance heat in the
air handling unit on most
installations.
Check
valve
Check
valve
TXV
TXV
Indoor coil
Outdoor coil
Drier
Calculating heat pump
air flow
(See Figures 14 and 15.) In
heating mode, the temperature
of the air leaving the indoor coil
will typically be 95°F (35°C).
This discharge air temperature
is lower than most types of
combustion heating systems.
It means that the heat pump
requires a greater volume of
indoor airflow to deliver the
same amount of heat. Each heat
pump system has a design
rating for air volume typically
given in cubic feet per minute
(CFM) or m3/sec (cubic meters
per second). If the airflow is too
low, the condensing temperature and pressure will increase,
causing an increased load on
the compressor. The airflow is
governed in part by blower
speed and duct-work sizing.
Most systems provide electrical
connection taps on the blower
motor to change speed. In order
to verify that the correct speed
is selected, the CFM (m3/sec)
should be measured. Mechanical methods are available but a
simpler electrical-temperature
method can be used on systems
that are equipped with electrical supplemental heat.
Start by setting the system
into the emergency heat mode
so that the compressor is off.
Next, use a Model 30 to measure the input voltage and current. These readings allow the
calculation of BTU/hour using
the following formula:
BTU/hour = Volts x Amps x 3.412
Compressor
Outside
air
Discharge
line
Return
air
Suction
line
Reversing valve
Figure 13. Heat pump. Shown here is a heat pump in heating mode.
Heat is collected from outside and transferred to the area to be heated
through condensation. The 4-way reversing valve allows the flow to be
reversed, turning the heat pump into a conventional cooling system.
12
Fluke Corporation HVAC/R Systems
Heat Pump Applications
Using a Fluke 52, measure
the temperature rise across
the heating element. To do so,
measure the inlet temperature
T2 and the outlet temperature
T1 simultaneously and use the
T1-T2 function to display the
difference. If possible, measure
the outlet temperature downstream from a bend in the
ductwork where the air has
been adequately mixed, thus
giving a more accurate reading,
or take an average of several
readings across the duct.
Using this temperature reading, plus the BTU/hour calculation above, calculate the airflow
as follows (see example in
Figure 15):
CFM =
(BTU/hour)
(1.08 * (T1-T2) )
Checking the defrost
control on the heat pump
points: Clamp the pipe clamp
thermocouple to the outlet of
the outside air coil, as close as
possible to the termination
temperature sensor coming from
the defrost controller board.
Either wait for a defrost to occur
or force a defrost by jumping
out the controller board per
manufacturer’s instructions.
Check the temperature when
the defrost cycle is initiated and
terminated. Check these readings against the manufacturer’s
recommended values. If the
temperatures are outside the
specified range, adjust to proper
operation temperatures (if possible) or replace the defrost
control.
On modern heat pumps, defrost
is accomplished automatically
with electronic defrost controller boards. Initiation of defrost
is done by time and temperature of the outside coil conditions. The temperature at which
a heat pump system goes into
defrost mode is usually preset
at the factory. However, the
time function for sampling if
defrost is required can be adjusted on the defrost logic
board by moving jumper pins.
Termination of defrost is done
by either temperature or time,
preferably by coil temperature.
Here’s how a Fluke 16
with the 80PK-8 Pipe Clamp
Thermocouple can be used to
verify the defrost start and end
Caution: Don’t condemn the defrost control
until the heat pump has been checked for
proper refrigerant charge. Heat pumps with
low charge will not have enough refrigerant
to adequately complete the defrost cycle.
T1 - Outlet air
64°F
1BTU
Measure voltage
and current
Heating element
63°F
52
K/J THERMOMETER
K
T1-T2
ON/OFF
T1
F/C
T2
HOLD
T1-T2
RECORD
VIEW
F
MIN/MAX
1 Wooden match
T1
60V
24V
MAX
T2
!
OFFSET
OFFSET
60V
24V
MAX
T1 - Inlet air
Figure 14. BTUs. BTUs (British Thermal Units) are a measurement
of heat. A BTU is the amount of heat required to raise a pound of water
one degree Fahrenheit at sea level. This is approximately the heat given
off by burning a wooden match.
Figure 15. Calculate the BTUs and CFM of a system. Measure the
input voltage and current. Then measure the temperature rise across the
heating element. In the example shown, a 240V system drawing 62.5A
produces a temperature rise of 47.4°F (8.5°C). Plugging these values into
the simple formulas (see text) yields 51,180 BTU/hr and 100 CFM.
HVAC/R Systems Fluke Corporation
13
Measuring Relative Humidity
Measuring relative
humidity
Take the dry bulb measurement by recording the temperature as you fan air past the
(See Figures 16 and 17.) Comfort thermocouple with a newspain a home or office depends on per or other object. Don’t blow
relative humidity as well as on
on the thermocouple because
air temperature. Even given the your breath is warmer than the
proper temperature, residents
air you are trying to measure.
or workers may experience dry
Take the wet-bulb measurethroats, dry skin, or excessive
ment by placing a clean 3"
static electricity if the relative
(7 cm) piece of wet cotton shoehumidity is too low. If the humid- lace over the thermocouple
ity is too high, condensation
(the lace serves as a simple
may form on windows and the
and inexpensive sock). The
air will feel damp. Humidity
sock should be saturated but
should usually be between
not dripping with clean water,
35% and 65% for reasonable
preferably distilled. If the sock
comfort.
is not saturated, an inaccurate
The relative humidity in an
reading may result. The thermoenvironment can be determined couple should be inserted about
by measuring wet-bulb and
half way into the sock.
dry-bulb temperatures. The
Fluke 51, 52, or Fluke 16
can be used to make these
measurements.
Fan air around the sock. The
temperature reading displayed
on the thermometer will slowly
decrease until the wet-bulb
temperature is reached. This
typically takes a minute or two.
Record the temperature.
Now use the psychrometric
chart to find the relative humidity. Start on the bottom axis at
the dry bulb temperature. Move
vertically along the dry bulb
temperature line corresponding
to your reading. Locate the
intersection of the diagonal
line that represents the wet bulb
temperature. The relative
humidity is indicated by the
curved line that runs through
the intersection of the two
temperature lines.
85
Grains of moisture
per pound of dry air
180
Dry bulb
52
K/J THERMOMETER
K
160
80
Fluke 80PK-4A
shrouded
air probe
F
T1
75
140
ON/OFF
F/C
T2
HOLD
T1-T2
RECORD
VIEW
52
K/J THERMOMETER
45
T1
F/C
T2
HOLD
T1-T2
RECORD
VIEW
MIN/MAX
Ambient air
20
Hu
m
id
ity
40
20%
30
35
ON/OFF
25
Fluke 80PK-4A
shrouded air
probe with
damp sock
60
%
30
40
F
80
%
K
T2
ti
la
Re
40
50
Wet bulb
100
ve
60
%
%
50
55
b
et
W
60
ul
b
MIN/MAX
70
9
8 0%
70 0%
%
120
te
m
pe
ra
tu
re
65
(°F
)
Ambient air
T1
10%
30
40
12.5 cu. ft.
50
60
13.0 cu. ft.
70
80
13.5 cu. ft.
20
90
100
14.0 cu. ft.
Dry bulb temperature (°F)
Figure 16. Relative humidity. Fluke 50 Series Thermometers can be
used to calculate relative humidity. Dry bulb measurements can be taken
directly (top drawing). A small piece of cotton shoelace quickly converts
a temperature probe so it can measure wet bulb temperature. Saturate
the shoelace and slip it about halfway over the probe. Then take the wet
bulb measurement. It may take a couple of minutes before the reading
stabilizes.
Figure 17. Psychrometrics. Psychrometrics is the science dealing with thermodynamic
properties of moist air and the effect of moisture on materials and human comfort. The
psychrometric chart is convenient for solving numerous process problems involving moist
air. Processes performed with air can be plotted on the chart for quick visualization as well
as for determining changes in significant properties such as temperature, humidity ratio,
and enthalpy for the process. The psychrometric chart provided here is a simplified version
that can be used for determining relative humidity at sea level. A slightly modified chart
can be used for other altitudes, depending on atmospheric pressure.
Psychrometric chart reprinted with permission from the Carrier Corporation.
14
Fluke Corporation HVAC/R Systems
Testing Combustion Heating Systems
Carbon monoxide
testing around
combustion systems
(See Figure 18.) Carbon monoxide is called the “silent killer.” It
is a colorless, odorless, toxic gas
whose primary source is the
incomplete combustion of fossil
fuels. Carbon monoxide can be
a potential problem in any
building that uses combustion
devices for space heating, hot
water heating, cooking, vehicles
such as propane forklifts, and
emergency power generation
equipment.
Gas heating equipment using
combustible gases such as natural gas or liquefied petroleum
(LP) require that the service
technician inspect the equipment annually for possible
carbon monoxide gas leaks into
the building. Using the Fluke
CO-210 Carbon Monoxide Probe
makes it easy to take accurate
measurements of CO levels
to determine if a there is a carbon monoxide gas leak into the
ambient environment.
For initial first pass analysis,
Troubleshooting using CO
the Fluke CO-210 can act as a
gas detection devices
High CO levels in the ambient
environment within the building can indicate problems such
as a cracked heat exchanger,
blocked/defective flue, or an
improperly ventilated/pressurized building. CO levels as low
as 200 parts per million (PPM)
can cause headaches, fatigue,
nausea, and dizziness over an
extended period of time. At 800
PPM of carbon monoxide, death
can occur in as little as 2 to 3
hours. Typically, there should
be less than 5 PPM in the ambient air within a building.
ASHRAE references a maximum
level of 9 PPM, while OSHA
mandates a maximum exposure
of 50 PPM for an eight-hour
work day.
stand-alone indicator. Simply
detach the CO-210 cord and
rely upon the device’s bright
LED and beeper that trigger
with increasing frequency (like
a Geiger counter) as CO levels
rise. The beeper can be turned
off when silent operation is
preferred. Use this method at a
supply register close to the furnace to check for a cracked heat
exchanger which is leaking into
the supply air system. If the
CO-210 “tick” rate increases,
then plug it into a digital multimeter with dc mV inputs to get
an accurate numerical readout.
The Fluke CO-210 measures CO
levels from 0 to 1000 PPM, with
an accuracy of 3%.
Next, use the Fluke CO-210
with a digital multimeter to
check for small shifts in ambient
carbon monoxide levels around
the exterior of the furnace and
along the flue vent. Keep in
mind that CO is lighter than air
and will rise from a leaky heat
exchanger or flue.
Figure 18. CO-210
w/79 Series III meter
testing ambient
carbon monoxide
levels around hot
water heaters.
HVAC/R Systems Fluke Corporation
15
Testing Combustion Heating Systems
The test procedure itself is
simple. Shut off the furnace and
locate the single wire between
the controller and the flame rod.
Typically, the wire is terminated
at the control panel or the flame
rod with standard spade connectors. Break the spade connection and place the test leads
from the Fluke 16 in series into
the circuit. Having alligator clips
for the test leads (such as the
Fluke AC70) will make the connection much easier. Turn on
the Fluke 16 Multimeter and set
the meter in the dc microamp
(µA) mode. Restore power to the
furnace (follow furnace
manufacturer’s instructions for
safe operation) and set the furnace to call for heat. Once the
burner or pilot ignites, check
your reading on the Fluke 16.
Refer to the furnace troubleshooting instructions to determine how to proceed with this
result. Typically, a low or zero
microamp reading may indicate
that the flame sensor is not
close enough to the flame, carbon build-up on the rod is limiting current flow (clean flame
rod with steel wool), the flame
rod is shorted to ground, continuity is not present between
the control module and the
flame rod (use the Fluke 16’s
continuity function to check),
or the control module is bad
and needs to be replaced.
Testing flame rods with
the microamp function
(See Figure 19 and 20.) Measuring microamps is required
regularly as part of the troubleshooting process when a flame
will not stay lit on a gas or oil
furnace. Most of today’s light
commercial and residential gas
burner controls utilize a flame
rod to confirm the presence of
the flame. Here’s how it works:
The control center sends out a
voltage to the flame rod. The
flame itself serves as a partial
diode rectifier between the
flame rod and the ground.
Without a flame, the circuit is
open and there is no current.
However, the presence of a
flame will allow a few microamps of dc current to flow. The
acceptable microamp reading
varies from one manufacturer
to another. Some controllers
such as the Honeywell Smart
Valve yield only 0.6 microamps
under full flame. However, it is
more typical to find readings
around 3 to 4 microamps such
as with the White-Rodgers
controller.
Figure 19. Fluke 16 in the microamps mode testing the flame
rectification circuit.
16 MULTIMETER
Gas Burner Controller
Flame Rod
RANGE
SELECT
MAX
MIN
TEMP
˚C / ˚F
V•Check
AC / DC
Furnace Burner
A
TEMPERATURE
Spade Clip gripped
by AC70 Alligator
Clips on TL75 Test
Leads
Figure 20. Depicting schematic of flame rod circuit with Fluke 16 in circuit.
16
Fluke Corporation HVAC/R Systems
Definitions
BTU
British Thermal Unit. The quantity of heat needed to raise the
temperature of one pound of
water one degree Fahrenheit
at sea level; approximately the
amount of heat given off by
burning one wooden match.
Bubble point
A term used with new refrigerant blends to indicate the refrigerant pressure/temperature
relationship at the outlet of the
condenser (i.e., liquid pressure).
Used when measuring for
subcooling on refrigerant blends
with temperature glide.
CFM
Cubic Feet Per Minute. A standard air flow quantification
used to describe air flow across
coils and through ducted fan
systems.
Change of state
The change of a substance from
one form to another, resulting
from the addition or removal
of heat. Changes of state due
to the addition of heat: liquid
to gas (evaporation), solid to gas
(sublimation). Changes of state
due to the removal of heat:
liquid to solid (freezing), gas
to liquid (condensation).
Condensing
The change of state from a
gas to a liquid. Heat is rejected
during this process.
Dew point
A term used with new refrigerant blends to indicate the refrigerant pressure/temperature
relationship at the outlet of the
evaporator (i.e., vapor pressure).
Used when measuring for
superheat on refrigerant blends
with temperature glide.
Evaporation
The change of state from a liquid into a gas. Heat is absorbed
during this process.
Heat pump
A compression cycle system
used to supply heat or cooling
to a temperature-controlled
space.
Heat pump balance point
The outdoor temperature at
which the heating capacity
of a heat pump in a particular
installation is equal to the heat
loss of the conditioned area.
High side
Parts of a refrigeration system
which are under condensing
or high pressure. Typically
from the compressor piston
discharge valves to the thermostatic expansion valve (TXV).
RH
Relative Humidity. The percentage of moisture in the air as
compared to the amount of
moisture in fully-saturated air
(i.e., 100% humidity) at the
same pressure and temperature
conditions.
Sensible heat
Heat energy which causes a
change in the temperature of
an object. Sensible heat can
be felt.
Subcooling
The difference between
the measured liquid line temperature of a refrigerant and its
condensing temperature at the
same pressure.
Superheat
The difference between the
measured suction line temperature of a refrigerant vapor and
its normal boiling temperature
at the same pressure.
Latent heat
Heat energy absorbed in the
change of state of a substance
Temperature glide
(melting, vaporization, fusion)
without a change in temperature. A term used with new refrigerant blends to give the range of
Liquid line
condensing or evaporating temperatures when the pressure
The tube or pipe that carries
remains constant.
liquid refrigerant from the
condenser (king valve) to the
TXV
refrigerant control mechanism
(TXV).
Thermostatic Expansion Valve.
A control valve that measures
Low side
and maintains a constant
superheat in the evaporator.
The portion of a refrigeration
system which is at evaporating It responds to a combination
of three forces: evaporator
pressure. Typically, from the
pressure, spring tension,
thermostatic expansion valve
and bulb pressure.
(TXV) to compressor piston
suction valves.
Ton of refrigeration
Refrigerant
The number of BTUs required
Substance used in a refrigerat- to melt a ton of ice in 24 hours:
One ton of refrigeration equals
ing system. It absorbs heat in
12,000 BTUs per hour.
the evaporator by a change
of state from a liquid to a gas.
It releases its heat in the condenser as the substance returns
from the gaseous state to a
liquid state.
HVAC/R Systems Fluke Corporation
17
Fluke Products
TRUE RMS MULTIMETER
79
RANGE
27 MULTIMETER
40
HOLD
26
87
V
16 MULTIMETER
Hz 20kHz
V 1kHz
k
30
0
12B
TRUE RMS MULTIMETER
CAL
MIN
mV
10
20
H
k
0
V
30
1
2
3
4
5
6
7
8
9
0
40
MULTIMETER
A
RANGE
REL
RANGE
MIN/MAX
HOLD H
40
RANGE
SELECT
MAX
MIN
TEMP
˚C / ˚F
OFF
Hz 20kHz
V 1kHz
REL
OFF
VoltAlert
1LAC-A
Hz
mV
40
mA
V
A
600V CAT
1000V CAT
mA/A
mA/A
10A
FUSED
AC / DC
V
A
!
10A MAX
AUTOMATIC
SELECTION
V
40
mA
!
1000V MAX
mA
A
mA
A
COM
V
OFF
A
TEMPERATURE
LOW IMPEDANCE
A
OFF
COM
A
CAT
mA
A
V
A
A
V•Check
H
Hz
V
V
mV
mV
HOLD
PEAK MIN MAX
mV
40
V
V
MIN
MAX
RANGE
RANGE
CAL
V
RESET
MIN MAX
MIN MAX
HOLD
MAX M
OFF
AVG
40
OFF
VDC
VAC
TRUE RMS MULTIMETER
100ms
Hz
!
320 mA MAX
COM
V
600V CAT
1000V CAT
10A
FUSED
10A MAX
FUSED
400mA MAX
FUSED
1000V MAX
!
COM
600V
+
COM
Fluke VoltAlert
1AC and 1LAC
• Two versions:
1AC for 90-600V ac
1LAC for 24-90V ac
• Detects voltage
without metallic
contact
• Easy to use—tip
glows red if voltage
is in the line
• Fits in a shirt pocket
for convenience
• 1 year warranty
• UL, CSA, CE, TÜV
listed
Fluke 12B
• Volts, ohms,
capacitance and
diode test modes
• MIN/MAX recording
with relative time
stamp
• Fast continuity
testing
• Millivolt range for
compatibility with
temperature and
other accessories
• Autoranging
• 2 year warranty
• Cat III 600V rating
• UL, CSA, CE, TÜV
listed
Fluke 16
Fluke 27
• Accurate temperature • Ruggedized,
measurement with
waterproof case
any K type
• Microamps for flame
thermocouple
sensor testing
• Microamps for flame • Volts, ohms, diode,
sensor testing
continuity, mA, and
10A modes
• Volts, ohms,
capacitance and
• MIN/MAX recording
diode test modes
• Millivolt range for
compatibility with
• MIN/MAX recording
with relative time
temperature and
stamp
other accessories
• Fast continuity
• Automatic Touch
testing
Hold®
• Millivolt range for
• Analog/digital
compatibility with
display
accessories
• Autoranging
• Autoranging
• 3 year warranty
• 3 year warranty
• UL, CSA, CE, VDE,
MSHA listed
• Cat III 600V rating
• UL, CSA, CE, TÜV
CO -210
CARBON MONOXIDE
PROBE
CAT
600V
600A
1000A
* Fluke 26 also includes
premium electrician test
leads with detachable
probes
MAX
400A
200 A
600 A
1000 A
200
HOLD
200 V
200A
400A
600 V
200
Fluke T5-600
Electrical Tester
• Quickly measures
volts ac and dc with
precise resolution
• Displays continuity
and resistance up to
1000Ω
• Easy and accurate
OpenJaw™ current
measurement up to
100A ac (0.5" jaw
opening)
• Compact design
with neat probe
storage
• Test leads feature
detachable probe
tips and accept other
Fluke test clips
• Hold button to freeze
display
• 2 year warranty
• Cat III 600V rating
• UL, CSA, CE listed;
VDE pending
18
Fluke Corporation HVAC/R Systems
Fluke CO-220
Carbon Monoxide
Meter/CO-210
Carbon Monoxide
Probe
• Quickly and accurately
measures carbon
monoxide levels up
to 1000 ppm
• CO-220 meter
features a large
backlit LCD display
• CO-210 accessory
works with a
multimeter with mV
inputs (output:
1 mV per ppm)
• Both feature a beeper
that ticks like a
Geiger counter
• Automatic sensor
zeroing and self-test
sequence upon
start-up
• Replaceable sensor
(typical sensor
life = 3 years)
• 1 year warranty
• CE listed
Fluke 79/26
Series III
• High accuracy
true-rms to assure
reliable readings
• New tapered
slimline design fits
great in your hand
• Permanent
overmolded case for
great durability
• Volts, ohms, diode,
capacitance,
continuity,
frequency, mA,
and 10A modes
• Millivolt range for
compatibility with
temperature and
other accessories
• Automatic Touch
Hold®
• Analog/digital
display
• Autoranging
• Lifetime warranty
• CAT III 1000V rating
• UL, CSA, CE listed;
TÜV pending
OFF
DC / AC
A ZERO
200V
Fluke 87
Series III
• The premier meter
of the industry!
• New brighter backlit
display with 20%
larger digits
• High accuracy
true-rms to assure
reliable readings
• Microamps for flame
sensor testing
• Volts, ohms, diode,
continuity,
frequency, mA,
and 10A modes
• 250 µS peak MIN/
MAX mode to
capture spikes
• MIN/MAX/Average
recording
• Millivolt range for
compatibility with
temperature and
other accessories
• Automatic Touch
Hold®
• Analog/digital
display
• Autoranging
• Lifetime warranty
• Cat III 1000V rating
• UL, CSA, CE, TÜV
listed
600V
OFF
36 CLAMP METER
30 CLAMP METER
DC
TRUE RMS
600V
600V
COM
V
Fluke 30
• Rugged enough to
take a fall from a tall
ladder
• AC volts, current,
ohms, and
continuity beeper
• Jaws accept cables
up to 1.5" in
diameter
• Data hold button
• 1 year warranty
• Cat III 600V rating
• UL, CSA, CE, TÜV
listed
Fluke 32
Similar features to the
Fluke 30 plus:
• True-rms to assure
proper readings in
environments with
non-linear loads
COM
V
Fluke 36
• AC/DC true-rms
clamp meter for
reliable readings
• Rugged enough to
take a fall from a
tall ladder
• AC and dc volts,
current, ohms, and
continuity beeper
• Tapered jaws (1.2”
diameter) allow
access into tight
spaces
• Max hold function
captures peak inrush current
• 1 year warranty
• Cat III 600V rating
• UL, CSA, CE, TÜV
listed
Fluke 80T-IR
• Fast, non-contact
infrared
temperature probe
• Works with most
multimeters with
mV inputs (1 mV
per °F or °C output)
• 0°F to 500°F
(-18°C to 260°C)
• Internal selection
switch for °F or °C
• 1 year warranty
Fluke 80i-400
• Measures ac current
from 1A to 400A
• Plugs into
multimeter with a
mA input (output:
1mA per amp)
• Accuracy:
± (3% + 0.4A) from
48 Hz to 1000 Hz
• 1 year warranty
• CE listed
Temperature Probes (Type-K Thermocouples) all cables 4 feet (120 cm) long
with stranded wire unless otherwise noted.
51 K/J THERMOMETER
52 K/J THERMOMETER
K
Model/Range
K
T1
HOLD
C
ON/OFF
MAX HOLD REC
T1
T2
T1-T2
T1
ON/OFF
F/C
F/C
T2
HOLD
HOLD
T1-T2
RECORD
VIEW
MIN/MAX
!
60V
24V
MAX
OFFSET
Fluke 51
• High accuracy
handheld
thermometer with
single input
• Works with any
K- or J-type
thermocouple
• Calibration pots on
the front allow for
simple field
calibration
• HOLD mode freezes
reading on display
• Selectable readout
in ºF or ºC
• Includes one
80PK-1 Bead
Thermocouple
• 3 year warranty
• CE listed
T1
OFFSET
OFFSET
METRIC
ENGLISH
E
ZERO
MP
TE
°C
°F
PV350
80PK-1
Air and
General Purpose Probe
-40°F to 500°F
(-40°C to 260°C)
Low cost bead probe for
general purpose temperature
measurement (solid
thermocouple wire).
Teflon insulation. Not suitable
for liquid immersion.
80PK-2A
Immersion Probe
-320°F to 1994°F
(-196°C to 1090°C)
General purpose immersion
probe for liquids or gels.
Not for food use. Inconel
sheath. Overall length 12.5 in
(32.75 cm).
80PK-3A
Surface Probe
32°F to 500°F
(0°C to 260°C)
Surface probe designed for flat
or slightly convex surfaces.
Teflon support piece.
80PK-4A
Air Probe
-320°F to 1500°F
(-196°C to 816°C)
Shrouded air probe for air
or gases. 316 stainless steel
baffle. Designed for insertion
into ductwork through a
typical balancing port.
80PK-5A
Piercing Probe
-320°F to 1500°F
(-196°C to 816°C)
Piercing probe for use in soft
or semi-hard materials.
Suitable for food use. FDA
approved 316 stainless steel
for food handling. Overall
length: 8.62 in (21.89 cm).
80PK-6A
Exposed Junction Probe
-320°F to 1500°F
(-196°C to 816°C)
Exposed junction probe—a
bead probe with a handle
for safe high temperature
measurement. Inconel sheath.
Overall length: 12.55 in
(31.87 cm).
80PK-7
High Temperature
Surface Probe
-197°F to 1112°F
(127°C to 600°C)
Ruggedized, high-temperature
surface probe made of 303
stainless steel with ribbon
sensor. Shaft can be
permanently bent to reach
difficult contact points.
80PK-8
Pipe Clamp
Thermocouple Probe
-20°F to 300°F
(-29°C to 149°C)
Pipe clamp temperature probe
measures temperature on pipe
surfaces from 1/4" to 1-3/8"
diameter (6.4 mm to 34.9 mm).
Rugged ribbon sensor.
60V
24V
MAX
Fluke 52
• High accuracy
handheld
thermometer with
dual inputs
• Works with any
K- or J-type
thermocouples
• Differential display
mode [T1-T2].
• Min/Max recording
of T1,T2, or [T1-T2]
• Calibration pots on
the front allow for
simple field
calibration
• HOLD mode freezes
reading on display
• Selectable readout
in ºF or ºC
• Includes two
80PK-1 Bead
Thermocouples
• 3 year warranty
• CE listed
OB
TK E PR
80 ERATUR
PRESSURE / VACUUM MODULE
F
OF
cmHg in Hg
kPa psi
OFF
Fluke 80TK
• Converts most
multimeters into
thermometers
• Selectable readout
in °F or °C
• Accepts a wide
variety of K-type
thermocouple
accessories
• Includes one
80PK-1 Bead Probe
Thermocouple
• 1 year warranty
Description
T2
!
60V
24V
MAX
Style
C
Fluke PV350
• Converts most
multimeters into
a high resolution
digital gauge
• Measures pressure
up to 500 psig
(3477 kPa)
• Measures vacuum
down to 29.9" Hg
(76 cm Hg)
(not intended for
micron measurement)
• Displays readings in
English (psig or "Hg)
or metric (kPa
or cm Hg)
• 1 year warranty
HVAC/R Systems Fluke Corporation
19
Electrical Tester, Digital Multimeter and Clamp Meter Selection Guide
Electrical Testers
Digital Multimeters
Clamp Meters
Models
7-300
7-600
T5-600
T5-1000
12B
16
27
77
26/79
87
30
32
36
Display Counts
4000
1000
4000
4000
3200
3200
4000
4000/20,000
2000
2000
2000
•
•
•
•
•
• Note 2
•
• Note 2
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Manual
Manual
Manual
•
•
•
Data Hold
Note 3
Data Hold
Note 3
Data Hold
Note 3
•
•
•
•
•
•
•
•
Note 1
Note 1
Note 1
• Note 6
• Note 7
• Note 5
•
•
•
Autoranging
Continuity Beeper
Automatic
Touch-Hold®
Data Hold
Note 3
Analog Bargraph
Special Features
Lifetime Warranty
True-rms
Backlit Display
Temperature
Note 1
• Note 4
Min/Max
•
• Note 4
Note 1
•
Min/Max Peak
Frequency
•
•
Offset/Relative Ref.
Sealed Case
Water/Chemical
Resistant
Note 8
Max Hold
Max Hold
Note 8
DC Volts
Max DC Voltage
300/600
600/1000
600
600
1000
1000
1000
1000
600
Best Resolution
1 mV
1V
1 mV
1 mV
0.1 mV
0.1 mV
0.01 mV
0.01 mV
0.1V
Max AC Voltage
300/600
600/1000
600
600
1000
1000
1000
1000
600
600
600
Best Resolution
1 mV
1V
1 mV
1 mV
0.1 mV
1 mV
0.1 mV
0.01 mV
0.1V
0.1V
0.1V
400 Hz
400 Hz
400 Hz
400 Hz
30 kHz
1 kHz
1 kHz
20 kHz
50/60 Hz
50/60 Hz
400 Hz
AC Volts
AC Frequency
Response
AC and DC Amps
•
•
•
•
Max Amps w/o
Probe Accessory
100A
(AC only)
200 µA
10A
10A
10A
10A
400A
(AC only)
600A
(AC only)
600A AC
1000A DC
Best Resolution
0.1A
0.1 µA
0.1 µA
0.01 mA
0.001 mA
0.01 µA
0.1A
0.1A
0.1A
Fused 10A Range
Other Electrical
Max Resistance
400Ω
1000Ω
40 MΩ
40 MΩ
32 MΩ
32 MΩ
40 MΩ
40 MΩ
200Ω
200Ω
200Ω
Best Resolution
0.1Ω
1Ω
0.1Ω
0.1Ω
0.1Ω
0.1Ω
0.01Ω
0.01Ω
0.1Ω
0.1Ω
0.1Ω
10k µF
10k µF
10k µF
5 µF
•
•
•
•
•
Max Capacitance
Diode Test
Conductance
Notes:
Standard feature
1 Temperature capable with 80TK accessory
2 Also includes Continuity Capture Mode
3 Data Hold does not automatically update
4 Min/Max plus relative time stamp
5 Min/Max plus Average
6 Frequency of voltage only
7 Lo-Ohms zero calibration subtracts test lead resistance
8 Partially sealed, splash and dust proof
•
•
•
•
Fluke. Keeping your world
up and running.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
U.S.A. (800) 443-5853 or
Fax (425) 356-5116
Europe (31 40) 2 678 200 or
Fax (31 40) 2 678 222
Canada (905) 890-7600 or
Fax (905) 890-6866
Other countries (425) 356-5500 or
Fax (425) 356-5116
Internet: http://www.fluke.com
©1998 Fluke Corporation. All rights reserved.
Printed in U.S.A. 12/98 10085-ENG-01
Printed on recycled paper.
20
Fluke Corporation HVAC/R Systems
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