Air conditioning diagnosis service and repair v2

Air Conditioning
Diagnosis,
Service & Repair

Copyright © 2011 Standard Motor Products, Inc. All Rights reserved.
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Portions of this manual COPYRIGHT © 2011 Standard Motor Products, Inc.
The material herein, may not be used without the prior express written permission of the copyright
holder, including, but not limited to reproduction or transmission in any form by any means such as
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as to its accuracy or completeness, nor is any responsibility assumed by Standard Motor Products, Inc.
for loss or damages suffered through reliance on any information contained in this volume.
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THIS VOLUME AND ITS CONTENTS.
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breaches or defaults arising out of the use of this volume. Customer agrees to indemnify Standard Motor
Products, Inc. and hold it harmless against all claims and damages, including without limitation,
reasonable attorney’s fees arising out of the use of this volume, unless such claims or damages result
from the infringement of any copyright or other proprietary right of any third party.

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TABLE OF CONTENTS
Introduction 5
Service Precautions 6
New Technologies R-1234yf (HFO-1234yf) 8
R744 (CO2) 9
SAE J2788 Recovery/Recycling/Recharging Equipment 12
Leak Detectors 13
Clutchless Compressors 14
Stretch To Fit Belts 16
Hybrid Vehicle Service 17
Service Tips Condenser Restriction Check 20
Belt and Tensioner Service
21
Ford Scroll Compressor Issue 21
Ford E Van Clutch Circuit Issues 22
Ford Diesel Van – Compressor Issue 23
GM Vehicles – In-the-Line Filter 24
Saturn – Rotary Vane Compressor Issue 25
Orifice Tube/TXV Dual Evaporator System Issues
26
GM Compressor Failure
27
Honda CRV Compressor Failure 27
Honda Condenser Issue 28
Honda CRV – AC Performance Issue 28
Dodge Truck – AC Clutch Issue 28

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TABLE OF CONTENTS continued
Service Procedures Compressor Replacement Steps 29
Lubrication
32
Compressor Oil Chart
33
Refrigerant Recovery, Recycling and Recharging
34
Recovery 35
Evacuation 39
System Charging 41
Flushing 43
Leak Detection
46
Trace Gas Leak Checking 50
Case Studies
Case Study #1. 1998 Jeep Wrangler – Compressor
Failure 50
Case Study #2. 2001 Ford F150 – Poor Performance In
Stop/Go Traffic 55
Case Study #3. 2001 Chevy Tahoe – Rear AC Issue 59
Reference Material Temperature Testing 63
Temperature Testing Flow Charts A, B and C 72
Determining TXV System Charge Level 75
VDOT System Testing 79
Temperature/Pressure/Humidity/Micron
Vacuum/Altitude etc - Charts and Worksheets 92

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INTRODUCTION
This class is designed to help you, the air-conditioning technician, diagnose and repair the refrigeration
circuit on most automotive AC systems using a variety of techniques including Maximum Heat Load
Temperature Testing. The course covers new HVAC technologies such as electronic variable
displacement compressors and a replacement refrigerant for R134a, best practice AC service procedures,
service tips and pattern failures. It also has several case studies that illustrate common AC service issues
and how to avoid them.
We do not focus on a particular manufacturer. The case studies are chosen because they illustrate
common failures or service missteps to be avoided.
The March of Technology and Its Impact on Air Conditioning Service and Repair
New HVAC technologies are constantly being introduced that make servicing air-conditioning systems
an ever more exacting science. Successful air-conditioning repair today requires attention to every detail
of the repair – recovery, evacuation, refrigerant handling, refrigerant and oil charge accuracy, system
flushing etc.
Manufacturers face three distinct pressures driving them to find ways to improve the efficiency of air
conditioning systems. Essentially this means getting the same job done with less – less refrigerant, less
oil, less fuel, less materials (lighter). As you can imagine, when you try to accomplish more with less,
every component in the system must perform at maximum efficiency all the time. This means that when
it comes to repairing these finely balanced systems, there is simply no margin for error at any step in the
repair process.
Here is a brief summary of some the pressures driving manufacturers to constantly fine tune and
improve HVAC technology:
• Because R134a is believed to cause global warming, manufacturers strive to make every
component in the AC system more efficient in order to use as little of the refrigerant as possible;
for example, by improving the heat exchange efficiency of the condenser and evaporator.
• There is a continuing incentive to improve CAFE fuel economy standards. Air-conditioning is
typically the largest single accessory load on the vehicle – any AC efficiency gain is indirectly a
fuel economy gain.
• Global warming again – burning fuel produces CO2, a green house gas. Manufactures receive
specific “AC credits” from the EPA for any technological AC system improvement that reduces
direct refrigerant emissions or reduces tail pipe (CO2) emissions. Therefore, any technology that
improves AC efficiency indirectly reduces CO2 production. Examples of this type of technology
are:
o Reduced reheat with the use of electronic variable displacement compressors
o Oil separators to reduce the amount of oil circulating in the system - oil coats heat
exchange surfaces reducing their efficiency.
o “Default to recirculate” when possible, to reduce wasted energy
o Use of internal heat exchangers

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o Ever smaller condenser tubes and complicated internal refrigerant routing.
o Electronic expansion valves.
o Greatly reduced system refrigerant and oil capacities
o The “Ejector Cycle” evaporator (Toyota).
Note: The greenhouse gas (GHG) effect of the CO2 produced by the extra fuel burned to drive the air
conditioning load is much greater than the GHG effect caused by the release of the refrigerant itself into
the atmosphere.
Service Precautions
Before proceeding with system diagnosis, the following precautions should be observed:
• Ensure that AC system pressure is released before opening the AC system at any point. The AC
system is under pressure and may cause personal injury.
• When using a jumper wire, ensure either the jumper wire or circuit is fuse-protected.
• Disconnect the battery cable before disconnecting a connector from any control module.
• DO NOT cause short circuits when performing electrical tests. This may set additional
Diagnostic Trouble Codes (DTCs), making diagnosis of original problem more difficult. You
could also severely damage or destroy electrical and electronic systems and components.
• Use specified test equipment when performing electrical tests.
• Follow OE manufactures specific safety procedures and directions when working on high
voltage (HV) hybrid vehicles. Be sure you have the right equipment for handling and testing HV
systems.

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NEW HVAV TECHNOLOGIES AND STANDARDS
Alternative Refrigerants – The Future of R134a
The refrigerant R12 is believed to have two detrimental environmental effects:
1. R12 depletes the ozone layer which prevents harmful Ultraviolet (UV) light from reaching the
earth.
2. R12 contributes to global warming by acting as a “Green House Gas” (GHG). R12 has a global
warming potential (GWP) of about 8100.
The introduction of R134a in the mid 1990s eliminated the problem of ozone depletion from this source
but did not completely eliminate the issue of global warming. R134a, although not an ozone depleter, is
also believed to contribute to global warming. Its GWP is calculated at about 1400.
For this reason, the European Union has banned the use of any refrigerant with a GWP of more than 150
in all new vehicle platform models after 2011 and in all new vehicles produced after 2017. This means
of course that R134a with its GWP of 1400 must be phased out in Europe over the next several years. At
this time, the use of R134a in the U.S has not been banned (see note later on state’s regulation of
R134a). However, to reduce production costs, OE new car manufactures would prefer to use just one
global refrigerant. It is likely therefore that the changes taking place in Europe will be felt in the U.S. At
least some of the vehicles you will work on in the next several years will almost certainly use a
refrigerant other than R134a. The refrigerant HFO-1234yf was approved in early 2011 under the EPA’s
Significant New Alternatives Policy (SNAP) program for approving non-ozone depleting refrigerants. It
is now legal to use subject to the EPA’s “Acceptable Subject to Use Conditions”. This means unique
vehicle service ports, labeling etc are required. HFO-1234yf will be known in the industry as R-1234yf.
See the notes on the following pages on R-1234yf and R744.
Refrigerant and automobile manufacturers have been searching for a suitable replacement for R134a for
several years. A number of alternatives have been proposed but none has met all the demands that would
be required of an acceptable alternative refrigerant. To meet international regulatory requirements and
be acceptable to car manufacturers, an acceptable alternative refrigerant would need to meet the
following criteria:
• Have no ozone depleting potential
• Have a global warming potential of less than 150
• Be non-toxic – chemically safe.
• Have low flammability
• Be reasonably compatible with existing HVAC technology – in other words have a similar
pressure/temperature and performance profile to R134a
• Be an effective refrigerant
Believe it or not, it has been extremely difficult to develop a chemical that meets all these requirements
completely. However, a new refrigerant, R-1234yf, has now been developed which does in fact meet
these criteria. It is now very likely to become the global replacement for R134a in new vehicles over the
next several years.

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R-1234yf (HFO-1234yf)
R-1234yf is a joint development of the Honeywell and DuPont chemical corporations. It has a GWP
value of only 4 compared to about1400 for R134a. Its temperature, pressure and performance
characteristics are very similar to R134a (see graph). It boils at -22.3°F versus -14.8°F for R134a.
Evaporator pressure for a temperature of 32°F is 31.4 PSI compared to 27.8 PSI for R134a. The
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) have given it
an A2L classification, which means mildly flammable. Extensive tests have shown it to be quite safe in
normal service circumstances.
Functionally, these characteristics make it a near “drop in” replacement for R134a. However, the
flammability issue will have some impact on system design, service equipment and technician training -
primarily from a safety perspective. Refer to the section later on the many new SAE “J” specifications
being developed to address the introduction of the new refrigerant. For example, evaporators intended
for use with R-1234yf must meet SAE J2842.
Lubrication and R-1234yf
It is expected that most systems will use a PAG oil similar to existing PAGs but with a special additive
package specific to R-1234yf. R-1234yf is chemically less stable than R134a and it is harder to maintain
oil miscibility in the system.
50/50 Mix
R-1234yf &
R134a
°F
PSI
R134a
R-1234yf
R-1234yf/R134a Pressure Temperature Relationship

9
R-1234yf Service Equipment
All new service equipment will be required including recovery/recycling/recharging equipment (SAE
J284 ), refrigerant identifiers (SAE J2912) and leak detectors (SAE J2913). Overall, however, because
of the basic similarities between the two refrigerants, equipment and service procedures will be similar
to working with R134a.
Vehicles will have all new high and low side service ports.
Recovery and recycling of R-1234yf will be required.
R-1234yf New Tank
A new tank of R-1234yf will be white with a red band toward the top.
R744 (CO2)
CO2 has been proposed as an alternative to R134a for a number of
years. The refrigerant itself is very acceptable from an environmental
perspective – it does not affect the ozone layer and has a GWP value
of only one. However, CO2 is not as efficient as R-1234yf (or R134a)
as a refrigerant. This means more energy is required to “drive” the
system to produce the same level of cooling. This reduces fuel
economy and drives up GHG tailpipe emissions of CO2!
Another drawback of CO2 is that its pressure/temperature profile is
vastly different from R134a. The static pressure in a CO2 system with the engine off on a summer day is
around 900 PSI! High side operating pressure could be as high as 2500 PSI. Therefore, CO2 requires
radically different (and expensive) system components than R134a. CO2 would require significant on-
vehicle safety systems to handle an accidental venting of the gas inside the passenger compartment.
Naturally, service equipment and procedures would be also very different.
For a while, some European manufacturers appeared committed to CO2. However, at this stage, it
appears unlikely that any OE manufacturers will adopt the use of CO2 in their vehicles. The majority of
automobile manufacturers favor the use
of R-1234yf. R744 (CO2) is however
still likely to be approved as a legal
refrigerant under the EPA’s SNAP
program.
New Vehicle Refrigerant Decal
Vehicles with R-1234yf will have a new
underhood air-conditioning system
decal. It will include the following
information:
New R-1234yf Tank Will be
White with a Red Band

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• Safety warnings
• The refrigerant type and capacity.
• Oil type
• SAE J639 – certifies that the system meets safety standards for “Motor Vehicle Refrigerant
Vapor Compression Systems.”
• J2842 - certifies that the evaporator meets safety standards for use in an R-1234yf system.
• J2845 – Indicates that the system should only be serviced by certified personnel trained in the
“Safe Service and Containment of Refrigerants”.
R-1234yf Evaporators
J2842 is a new SAE design and certification standard, for
evaporators intended for use with R-1234yf or CO2. The
new specification was developed because of the
flammability risk (mild) associated with R-1234yf and the
high pressures and possible poisoning in the event of an
in-cabin release of CO2. J2842 evaporators must carry a
label that indicates that that they must be discarded if
removed from the vehicle for any reason and that they
should only be serviced by certified personnel. Replacing
a J2842 evaporator with a junkyard unit would not be
permitted.
R-1234yf Recovery/Recharging/Recycling Equipment
SAE J284 is a specification for recovery/recycling/recharging equipment for servicing R-1234yf
systems. Here are some of the features of J2843 equipment:
• Arc resistant switches.
• Special ventilation since R-1234yf is flammable (mildly).
• Leak testing capability - the machine must perform both a vacuum and a pressure leak check
during evacuation and charging respectively.
o Vacuum leak test - hold a steady vacuum for two minutes after evacuation.
o Pressure leak test - the machine charges 10% of the system charge and monitors for
pressure decay before completing the charging cycle. The machine will halt the charging
cycle if the system fails this test.
o The equipment must have a built in refrigerant identification capability to prevent
accidental cross contamination of refrigerants.
Note: The issue of refrigerant identification may become an issue later. As R-1234yf vehicles become
more common, the possibility of cross-contaminated R-1234yf and R134a is likely. The static pressure
in a tank of R-1234yf/R134a cross contaminated recovered refrigerant will be slightly higher than in a
tank of either refrigerant on its own. This could result in the auto air-purge function of the
Type of Refrigerant
R-1234yf or CO2 Manufacturers
Logo
New SAE J2842 Decal for Evaporators

11
recovery/recycling equipment (for either refrigerant) bleeding off the entire tank of recovered
refrigerant.
Retrofitting and R-1234yf
At this time, there are no plans to retrofit older vehicles with R-1234yf because of the flammability
concern. R134a will continue to be available to service vehicles that use it.
More SAE “J” Standards
Most of the following SAE standards relate to the introduction of R-1234yf :
J639. This is a broad safety design standard for motor vehicle “Refrigerant Vapor Compression
Systems.” It has been recently revised to include standards for R-1234yf.
J2845. This standard details the training requirements for technicians working on R-1234yf and CO2
systems – especially as it relates to safety and refrigerant handling.
J2099. This is a refrigerant purity standard for recycled R-134a and R-1234yf.
J2297. This is a stability and compatibility standard for fluorescent refrigerant leak detection dyes for R-
134a and R-1234yf systems using ultraviolet leak detection.
J2911. This is a broad industry standard certifying that required SAE “J” standards for mobile air-
conditioning system components, service equipment, and service technicians have been met. It provides
assurance to regulators and customers that equipment, etc delivers advertised performance.
J2670. Stability and compatibility criteria for additives and flushing materials intended for aftermarket
use in R-134a and R-1234yf systems.
J2762. This standard certifies a method for removal of refrigerant from an air conditioning system to
quantify the charge amount.
J2842. This is a new design and certification standard for R-1234yf and CO2 evaporators described
earlier.
J2843. New standard for recovery/recycling/recharging equipment – details described earlier.
J2851. Similar to J2843 but for recovery only equipment.
J2912. New performance criteria for R-134a and R-1234yf refrigerant identifiers.
J2913. New performance criteria for R-1234yf electronic leak detectors.
J2927. A standard for refrigerant identifiers installed in R-1234yf Recovery/Recharging/Recycling
machines.

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SAE Standards for R134a Service Equipment
SAE J2788 Recovery/Recycling/Recharging
Machines
SAE J2788 is the current standard for R134a
Recovery/Recharging/Recycling equipment. The
standard was introduced several years ago for a number
of reasons.
Several studies indicated that older equipment could
leave as much as 30% of the old refrigerant in the
system during a typical recovery procedure. If the
service process was short-circuited by going straight
from recovery to recharge (without evacuation) then the
potential for a serious overcharge was high. On top of
this, the continuing trend toward ever-smaller system
charge capacities meant there was less room for even
small errors in refrigerant charging amounts. System
capacities of 12 to 16 ounces are common. An error of
just an ounce or two in either direction can result in
catastrophic compressor damage and system
performance issues. Today, exact system charge level is
critical for successful AC service. Machines manufactured to meet J2788 ensure much more complete
recovery of refrigerant. They also ensure much more accurate metering of the exact charge amount.
Compliant machines must recover at least 95% of the refrigerant in 30 minutes. J2788 machines have a
charge tolerance of +/- 0.5oz. Older machines were significantly less accurate.
An undercharged system can cause poor compressor lubrication and catastrophic failure and of course
poor performance.
An overcharged system can cause liquid slugging of the compressor and compressor damage, high
system pressures, high vent temperatures and compressor cut-out switch activation.
J2788H
The “H” suffix denotes hybrid. This is a specification for recovery machines intended for use on hybrid
vehicles that use a High Voltage (HV) electric compressor. The idea is to prevent oil cross
contamination between conventional AC systems that use PAG oils and HV compressors that use an
ester based oil. Ester based oil is used in HV systems because of its superior dielectric properties over
PAG. If even a small amount of PAG (as little as 1%) were to contaminate a HV system, a high voltage
leak could occur. This can result in a complete vehicle shut down and severe damage to the system.
Refer to the “Hybrid” section below for more information on this issue. Typically, these machines come
with an adapter that enables liquid refrigerant to be circulated through the service hoses to flush any
traces of PAG oil before servicing a high voltage system.
J2788 & J2788H Compliant
Recovery/Recharging/Recycling Machine

13
J2791 and J2913 Electronic Leak
Detectors
Because of reduced charge capacities,
even a small leak can result in a
performance issue and possible
compressor damage much more quickly
than the same leak on a larger capacity
system. The need to detect ever-smaller
leaks has become much more critical.
In response to the need for more reliable
and accurate leak detection, SAE
International published J2791 for R134a
electronic refrigerant leak detectors
several years ago. J2791 leak detectors
can find leaks as small as .14 oz/year (4
grams) per joint. The old standard was .5
oz (14 grams). They are also less
sensitive to false triggering and are more robust.
Note
SAE has now issued a new standard, J2913 for R1234yf leak detectors. Detectors meeting this standard
must be able to differentiate between a 4, 7 and 14 gram leak (approximately 0.141, 0.247 and 0.5oz).
Some detectors meet both J2791 and J2913 standards.
State Regulations – R134a
California (and possibly other states) is proposing to introduce their own restrictions on the use of R134a
similar to those underway in Europe. Their proposal would likely require the use of a low GWP
refrigerant in new vehicles.
Wisconsin has had a law in place since October 1994 prohibiting sales of container sizes holding less
than 15 lbs of R134a. However, this restriction applies only when the chemical is intended to be used as
a refrigerant. For example, it is legal for a person to purchase gas duster containers with any amount of
the chemical because in that instance, the chemical is neither intended to be a refrigerant nor is HFC-
134a included in the listing of Class I and Class II substances.
J2791 Electronic Leak
Detector for R134a
Refrigerant
Combination J2913
and J2791 Leak
Detector – Detects
R134a & R1234yf

14
Electronic Variable Displacement Clutchless Compressors
In the past several years, a number of manufacturers
have started using a new computer-controlled
compressor. This design of compressor is gradually
becoming standard on many vehicles. Chrysler/Jeep,
GM, Toyota, Nissan, ME/BE, Audi/VW and Kia
have used it on different models. The basic design is
similar to a conventional wobble plate variable
displacement compressor. The key differences are:
1. To control compressor displacement, they
use a pulse width modulated solenoid,
controlled by the computer. This solenoid
replaces the conventional control
valve that responds to suction line
pressure. The computer varies the
duty cycle command to the solenoid
to route more or less pressure to the
rear of the pistons to change the
angle of the wobble plate. In this
way, the pumping capacity of the
compressor can be varied from
almost zero to maximum capacity
(1% - 100%).
The computer takes account of a
range of inputs to decide the
appropriate compressor
displacement. It can optimize the
system for best air-conditioning,
fuel economy and engine performance. Depending on the system design, it can monitor
evaporator case temperature, system pressures, ambient and cabin temperatures, driver inputs
etc.
When the Wobble Plate Is at an Angle to the Shaft, the
Piston Stroke Is at Maximum
Maximum
Stroke
When the Wobble Plate Is at Right Angles to the Shaft,
the Piston Stroke Is Almost Zero
Piston Stroke
Reduced to Zero
Variable Displacement
Control Solenoid
Electronic Variable
Displacement Compressor
Electronic
Control Valve
No Clutch

15
2. There is no electric clutch – the compressor shaft turns all the time when the engine is running,
even with the AC off. Lubrication is especially critical.
Note: The system must be properly charged with refrigerant and oil at all times to maintain
adequate lubrication
These compressors are designed to keep more of the oil charge circulating within the unit to
maintain lubrication even when the AC is off. The compressor pulley contains a damper to
absorb engine torque fluctuations and a limiter mechanism that allows the spoke portion of the
pulley to break away in the event that the compressor locks up. This allows the compressor
pulley and any other
accessories driven by
the same belt to continue
to turn.
Electronic Variable
Displacement - Compressor
Control
The computer varies the duty
cycle command to the
compressor control solenoid to
match the heat load on the
system. When the heat load is
high, the computer increases the
“On” command to the solenoid.
The oscilloscope patterns
shown here illustrate the
command to the solenoid at idle
on a 2008 Dodge Caliber during
both low and high heat load
conditions. The solenoid is
permanently grounded and is
positive pulsed by the computer.
Quick Tip:
The computer is in complete
command of the compressor
pumping displacement. If you
find that the compressor does not
appear to be building pressure,
even after evacuating and
recharging the system, do not
immediately condemn it. The
computer may not be sending the
correct signal to the solenoid.
Solenoid + Duty
Cycle = 87%
Solenoid Current = 0.8A
High Heat Load – Greater Duty Cycle Command to Solenoid
(87%). Solenoid Current = 0.8A
Solenoid + Duty
Cycle = 43%
Solenoid Current = 0.4A
Low/Medium Heat Load – Medium Duty Cycle Command to
Solenoid (43%). Solenoid Current = 0.4A

16
For example, if the solenoid is unplugged, the compressor defaults to minimum displacement – about
1% of capacity. Check for HVAC and engine management system trouble codes that might be inhibiting
AC operation. Check also for inaccurate sensor inputs that might cause the computer to send the
incorrect command to the solenoid – e.g. inaccurate system pressure sensors, inaccurate evaporator or
ambient/cabin temperature sensor readings.
Stretch to Fit Belts
General Motors started using “Stretch to Fit Belts”
on the 2008 Hummer H3 and 2009 full sized
trucks: Silverado, Avalanche, Tahoe, Suburban,
Express Van, Sierra and Yukon.
They are also used on midsized pickups and SUVs
such as the Colorado, Trailblazer, Canyon and
Envoy and on Saab 9-7 and Cadillac CTS-V.
Ford uses stretch to fit belts for the power steering
on 2008 and up Edge, MKX, Fusion, Milan MKZ
and MKS with 3.5/3.7L engines.
Chrysler uses stretchy belts on the power steering
pump of 2007 and up 2.7L engines.
The belt is very similar in appearance to a
conventional serpentine belt. However, the
reinforcing cord is made of a polyamide material which is more elastic than the aramid or polyester cord
used in traditional belts. The Polyamide cord, when combined with a more elastic backing compound,
gives the belt it's “stretch” quality. As a result, the belt is able to maintain proper tension throughout its
life without the use of a tensioner.
Note: GM states that once
the engine is operated with
the stretch belt installed, the
belt cannot be removed and
reused. It is designed to be
removed by cutting it off.
Ford and Chrysler indicate
that the belts can be reused
provided special tools are
used to remove and
reinstall the belts.
Removing Stretch to Fit Belt on GM
Vehicles
Using Special Tool to Install Stretch to Fit Belt on GM Vehicles
Several Manufacturers Make a Tool for This Purpose
Belt Installation Tool
Belt Installation Tool

17
Hybrid Vehicle AC Service
Safety: Servicing hybrid air-conditioning systems requires special
precautions over and above normal AC service. There are many
flavors of hybrid vehicles using a range of voltages from 42 to almost
400 volts. Many use high voltage to drive an all-electric compressor.
High voltage (HV) can be lethal. Each manufacturer has specific
safety procedures that must be followed when working on their
particular HV vehicle. Working on hybrid vehicles requires special
attention in three main areas:
1. Servicing HV system or components – this
includes working on the HV compressor used on
many Hybrids. Hybrid vehicles have HV
disconnect plugs or switches to disable the HV
system. Always follow the specific procedures
for making the HV system safe to work on.
When working on a HV system you will need
some dedicated safety gear and equipment.
Always wear a pair of HV class 0, 1000 volt
rubber gloves. Electrical system checks should
be made using a CAT III rated DMM. The meter
leads must also be rated for 1000V.
2. Idle Stop System. The gasoline engine may not
always be running on a hybrid vehicle. It can start up unexpectedly any time the system is “on.”
To avoid potential injury or damage, always follow the OE manufactures procedures to prevent
unexpected gas engine start-up while working on the vehicle.
3. HV Compressor Lubrication. HV compressors use a special formula polyolester (POE) oil.
POE oil is used because of its high dielectric
qualities. The motor windings of high
voltage compressors are exposed to the
refrigerant and oil. Extra care must be taken
to avoid any contamination entering these
systems. If the oil becomes contaminated,
high voltage can find a path to ground
through the oil. The vehicle management
system will set high voltage leakage codes
and may completely disable the vehicle - it
might not start at all. Repairing the vehicle
may require replacing every component in
the refrigerant path – compressor,
condenser, evaporator etc.
Note: Just 1% of PAG contamination in the POE oil
A Bright Orange Cable Connected to the
Compressor Indicates High Voltage
Toyota Prius
CAT III DMM
Class 0, 1000V
Rubber Safety Gloves

18
in a hybrid system can compromise the dielectric strength of the POE oil. PAG oil residue from the
service hoses of your equipment could allow this to happen. You should only use
Recovery/Recycling/Recharging equipment meeting SAE specification J2788H -
the H suffix stands for “hybrid.” This equipment is designed to avoid hybrid HV
AC system contamination. See page 12 for more detail on these machines. Use a
separate, dedicated oil injector to install the POE oil into a HV system (unless your
equipment manufacturer expressly states that their machine can handle this task).
However, once you know the proper procedures for working with the high voltage
system and take care to avoid oil cross contamination, then working on hybrid HV
air-conditioning is much the same as working on conventional air-conditioning.
Outside of the electric compressor, most of the other components in the system are conventional.
Components can be
replaced and the system
serviced using conventional
tools and techniques.
Note: Some Honda Hybrid
vehicles use a combination
belt driven and high
voltage electric motor
driven compressor. The
front half of the compressor
is a belt driven scroll and
accounts for about 85% of
the compressor pumping
capacity. The rear half is a
brushless electric motor
driven scroll. It accounts
for about 15% of the
compressors capacity.
During idle-stop operation,
when the gas engine shuts
off, the small electric motor
scroll can provide temporary air-conditioning assist. The point is that just because you see a belt, don’t
assume that it is a low voltage compressor.
Caution: Even after following the high voltage disable procedure use a Cat III DMM while wearing HV
gloves to check that there is no voltage present at the system or component you are about to work on.
About Hybrid Compressors
Hybrid vehicles may use one of three basic compressor types:
1. A conventional 12V, belt driven compressor with a clutch, similar to a normal AC system.
2. A high voltage AC or DC compressor. These compressors are driven by the same high voltage
used for the vehicle propulsion system. They are easily identified by the bright orange cables
attached to the compressor. They do not have a belt and may run when the gas engine is off.
15% Pumping Capacity
Belt Driven Scroll
HV Electric
Motor Scroll
85%Pumping Capacity
Suction Discharge
Honda Combination Belt and Electric Motor Driven Scroll Compressor

19
3. A combination belt driven and high voltage compressor (used on some Hondas) as described
above.

20
SERVICE TIPS AND PATTERN FAILURES
Quick Restricted Condenser Check.
Many later model vehicles use a high side pressure transducer. The transducer is usually located on the
compressor discharge line while the high side service port is located on the liquid line. By comparing
high side pressure indicated on the scan tool (discharge pressure) versus gauge pressure (liquid line
pressure), you can get some indication if the condenser is restricted. Note that some pressure drop across
the condenser is normal. Actual normal pressure drop depends on several factors, including heat load on
the system, system design, etc. You will need to gain some experience using the technique by checking
known good vehicles regularly.
Read Liquid
Line Pressure
on Gauge Set
Condenser Restriction Check – Compare Discharge Pressure on Scan
Tool to Liquid Line Pressure on Gauge – Note: Some Drop Is Normal
Read Discharge
Pressure on Scan Tool
Pressure
Transducer
High Side
Service Port

21
Belt and Tensioner Service
Typically, the air-conditioning compressor is the largest
single accessory load on the vehicle. Each component in
the accessory belt drive system (ABDS) must be in good
condition to ensure smooth compressor operation.
The belt tensioner performs two distinct functions:
• Maintain correct tension on the drive belt
• Dampens torque fluctuations in the ABDS system
caused by the engine firing, the compressor and
other accessory loads.
The tensioner can fail in several ways: the spring may lose
tension causing belt slippage, wear and squealing. The
damper can fail causing excessive belt slap and vibration.
The pivot bushing and/or pulley bearing can fail causing
uneven belt wear and alignment issues.
The circumstances leading up to compressor failure often
put the tensioner under excessive strain. AC head pressure
may be very high causing the tensioner/damper assembly to bottom out repeatedly and fail. When the
compressor is replaced, a belt slippage or vibration problem can be
attributed to the replacement compressor when in fact the problem is due
to the failed tensioner assembly.
A careful check of the tensioner, the belt and other ABDS components
should therefore be performed. The alternator and fan clutch are also
substantial loads on the system. Their operation should also be checked.
Note: Most modern belts are made from an EPDM material which may
not show classic signs of belt failure such as cracking. The friction
surface may look OK yet be badly worn.
ABDS Quick Tip
Diagnosing ABDS squealing/chirping noise: with the engine running,
use a water spray bottle to spritz the underside of the drive belt. If the
noise gets worse, it is probably a belt tension issue; if the noise is
reduced, it is probably an alignment issue in the ABDS.
Ford Variable Displacement Scroll Compressor Issue
2005 – 2007 Ford Five Hundred, Freestar and Montego models use
a variable displacement scroll compressor. The compressor
capacity can be infinitely varied between 30% and 100% of output.
Variable displacement is achieved with a spool type control valve,
with an integral bellows. The bellows expands and contracts in
response to suction line temperature/pressure. This moves the
control valve back and forth. As the valve moves, more or less
refrigerant is allowed to recirculate inside the compressor to vary
output. The control valve bellows can fail resulting in reduced
Ford Scroll Compressor –
Control Valve Can Fail
Causing Reduced Output
The Compressor Is the Largest
Accessory Load – ABDS Must be in
Good Condition to Drive It
Belt Tensioner: Check
Spring Tension, Damper
Function, Pivot Bushing
& Bearing Wear

22
compressor output. High side pressure will be low and low side pressures will be high with poor
performance. The compressor is sensitive to minute amounts of contamination that can cause the valve
to stick – important to keep in mind when flushing.
Ford E Vans - Mid 1990’s - 2004
Air-conditioning and Drivability Issues
Depending on the time of year, the customer may complain of some or all
of the following symptoms:
• No AC operation
• Poor defrost function
• Surging idle
• Repeat AC clutch failure
If the problem occurs during the
winter, the symptom is usually a
surging idle or poor defrost
function. During the summer, the
symptom is usually no AC
operation.
Refer to the wiring diagram on
this page. Note that the AC clutch
voltage must cross four switches
before reaching the clutch. Note
also that three of the switches
would be cycled frequently
during normal use: the ignition
switch, the AC mode switch and
the clutch pressure-cycling
switch. With so many active
switches in series, the potential
for a substantial cumulative
voltage drop in the circuit is high.
If the AC cycling pressure switch
starts to fail, several symptoms
can occur.
• As the voltage drop across
the failing switch contacts
increases, the available
voltage at the clutch
decreases. Eventually the
clutch starts to slip, burns
up, and finally fails. It
may also take out the
compressor due to warping of the compressor case or failure of the front seal from the excessive
AC
Clutch
Function
Selector
Switch
AC Clutch
Cycling
Pressure
Switch
PCM
Hot In
Run
AC
Pressure
Cutout
Switch
Clutch
Diode
AC Clutch Circuit Has Four Switches in Series –
Increased Likelihood of Large Voltage Drop

23
heat generated by the slipping clutch. If the clutch or the compressor are replaced without the
underlying cause of the original failure being identified a repeat failure is likely to occur.
• When the voltage drop across the cycling switch becomes so great that there is not enough
current to engage the clutch, then another unusual symptom can occur. When the AC (or defrost)
is first turned on, current starts to build in the clutch circuit. However, the failing cycling clutch
switch contacts are not able to carry the rising current and the switch goes open almost instantly.
The clutch never actually engages.
Note from the wiring schematic, that there is a splice off the AC clutch circuit after the cycling
switch that goes to terminal 41 at the PCM. This is the AC “On” input to the PCM. It signals the
PCM to raise the idle to compensate for the air-conditioning load. However, in this case the PCM
only sees battery voltage on the circuit for an instant before the failing switch contacts break
apart because they cannot handle the rising current flow. The PCM raises the idle speed in
anticipation of the AC coming on, but lowers it again an instant later when the input signal goes
away at pin 41. When the switch contacts cool off, they come back together momentarily and the
cycle starts over again. The typical symptom is a regularly surging idle when the AC or defrost
are turned on. This can be a tricky diagnoses, especially during the winter when you might not be
thinking about air-conditioning!
Quick Tip: This circuit configuration was used by Ford for about ten years and similar versions even
longer. There is a strong likelihood of a substantial voltage drop developing in the circuit as the vehicle
ages. It can cause any or all of the symptoms described above. It is a good idea to check the voltage drop
at the AC clutch on these vehicles when performing any kind of AC service - especially when replacing
the clutch or the compressor. The voltage should never be less than 12V with the engine running and
ideally should be within one volt of system voltage. This is also a good check to perform as part of a
preventative maintenance check of the air-conditioning system.
If the customer’s concern is a surging idle, monitor the “A/C Cycling Switch” input PID on a scan tool.
If the PID momentarily changes to “On” intermittently, suspect that the cycling pressure switch may be
no good.
2004 - 2006 Ford 6.0L Diesel E 350/450 Vans
AC Compressor Failure.
The AC compressor may fail. The compressor on these vehicles is a low mount scroll design. They are
particularly sensitive to charge level – either an undercharge or overcharge. To correct the problem,
Ford has revised the refrigerant and oil capacities and also issued a calibration update for the PCM. The
refrigerant charge capacities have been reduced to prevent slugging and the oil capacity of the single
evaporator system increased to improve lubrication.
On front AC only systems, the refrigerant charge level has been reduced to 32oz from 40oz and the oil
charge level has been increased to 11 oz from 9 oz.
On dual AC systems, the refrigerant charge level has been reduced to 54oz from 60oz. The oil charge
level remains the same at 13 oz.

24
Note: When scroll compressors suffer a catastrophic failure, they create a lot of debris. It is usually
necessary to replace the condenser in conjunction with the orifice tube and the accumulator. All other
components not being replaced should be thoroughly flushed including the evaporator.
2007 and Later GM Vehicles – In-the-Line Filter
Starting in 2007 GM began phasing in an in-the-
line liquid line filter on various vehicles – both
cars and trucks. At first glance the filter looks
very similar to an orifice tube. However, it is just
a filter and there will be a separate orifice tube or
TXV valve in the system. The filter simply slips
into the line much the same wasy as an orifice
tube. It is usually installed at at coupling in the
liquid line. The filter can be found in various
locations – at the condensr outlet, just before the
expansion device before the fire wall and on some
dual evaporator applications it is located in the
liquid line just before the rear TXV valve. The
key is to be aware of it. If the compressor fails the
filter will almost certainly be clogged. It must be
replaced.
Starting 2007 - GM In-the-Line Filter
Located in Liquid Line

25
Rotary Vane Compressor Issue
Saturn and Other Vehicles that Use a Rotary Vane
Compressor
The customer concern is usually poor AC
performance. High side pressure will be lower than
normal and low side pressure will be higher. The
problem often occurs after the air-conditioning system
has not been used for some time. It can also occur
immediately after a new or remanufactured compressor is installed. Normal diagnostics will indicate that
the compressor cannot build pressure.
Refer to the picture on the right of a rotary vane compressor with one end
removed.
When you turn a conventional piston design compressor by hand, even
slowly, you can feel the suction and pressure forces at the suction and
discharge ports. However, for a rotary vane compressor to start pumping,
the vanes must be thrust out against the rotor sidewalls by centrifugal
force. The rotor must be turning rapidly before the compressor starts to
pump.
When the compressor is unused for a while, the vanes may seize in their
slots and not slide out against the rotor sidewalls. The problem can also
occur in a perfectly good new or remanufactured compressor if it has
been in storage for a while. Before condemning the compressor, try the
following procedure to free the vanes:
• Charge the system with half the specified amount of refrigerant.
• Raise the engine speed to 2500 RPM.
• Cycle the compressor on and off every few seconds while monitoring system pressures. If the
rotor vanes are stuck, this procedure will usually dislodge them and the compressor will start
pumping again.
• When the compressor starts to build pressure, add the remaining refrigerant to bring the system
up to full charge. Perform a maximum heat load temperature test to confirm that the system is
performing efficiently.
Note: Variable displacement compressors such as GM V5 and V7 units can suffer from a similar
problem. The wobble plate can stick at a shallow angle - usually after a period of disuse. The problem
can usually be corrected with the technique outlined above for rotary vane compressors.
Both rotary vane and wobble plate design variable displacement compressors are especially sensitive to
oil viscosity.
The Rotor Vanes
Can Stick In the Slots

26
Orifice Tube/TXV Dual Evaporator System Issues
Here are several issues that affect General Motors Dual evaporator systems that use an orifice tube in the
front and a TXV in the rear (OT/TXV). These issues can also arise on other manufacturers’ platforms
that use a similar system.
1. These OT/TXV dual evaporator systems use an accumulator instead of a receiver/drier. This
means there is no filter in the liquid line between the condenser and the rear TXV valve. (Note:
Starting about 2007 GM began putting a small in-the-line filter in the liquid line of some
vehicles). After a catastrophic compressor failure, it can be difficult to flush all the debris from
the long lines that snake the length of the vehicle. Even with a good flushing process, some
debris can remain in the lines – especially in the liquid line. For this reason, it is highly
recommended that an inline filter be installed in the liquid line just before the rear TXV. The
filter should be installed in addition to flushing – it is not a substitute for it. Refer to the 2001
Chevy Tahoe case study on page 59 for more information on this issue.
2. Refer to the dual evaporator system schematic above. Note that the rear evaporator suction line
returns directly to the compressor – it is not routed through the accumulator. If liquid refrigerant
or oil passes through the rear evaporator, they will return directly to the compressor and possibly
slug it – severe damage can result. These systems are more prone to slugging in moderate
climates during low heat load conditions.
3. Another issue on some systems of this design is that the rear TXV thermal bulb can separate
from the evaporator outlet line. The TXV “interprets” this as increased heat load and responds by
metering more refrigerant into the evaporator. The excess liquid refrigerant can slug the
compressor causing severe damage.
Orifice
Tube
Condenser
Front Evaporator
Rear
Evaporator
Accumulator
TXV
Note that Rear Evaporator Suction Line Returns Directly to
Compressor – Exact Charge Is Critical to Avoid Slugging
Protect TXV after
Compressor Failure -
Install Inline Filter
Here
TXV Thermal Bulb Detached from Suction Line
Can Cause Compressor Slugging

27
Various GM Trucks and Cadillac CTS 2002 – 2004
Compressor Noise/Failure
Affected Models:
2003-2004 Cadillac CTS
2002-2004 Cadillac Escalade and Escalade EXT
2003-2004 Cadillac Escalade ESV
2002-2004 Chevrolet Avalanche, Express, Silverado, Suburban, and Tahoe
2002-2004 GMC Denali, Denali XL, Savana, Sierra, Yukon, Yukon XL
2002-2004 Commercial Upfitter Chassis Vehicles
The symptoms vary depending on how far the failure has progressed:
• The compressor may have failed outright and is inoperative.
• The serpentine belt and tensioner may be slapping or vibrating excessively.
• Pressure gauges (especially the high side gauge) may be vibrating/bouncing excessively.
• The compressor may be making a rattling noise, especially on acceleration.
The original compressors on these vehicles are prone to liquid slugging. Broken reed valves in the
compressor usually cause the belt vibration and pressure pulsations described above.
For a lasting repair, the compressor, condenser, orifice tube, accumulator and rear TXV may need to be
replaced. Any sections of the refrigerant path not being replaced, including both evaporators on a dual
system, should be thoroughly flushed. On a dual evaporator system, the installation of an inline filter
before the rear TXV is strongly recommended. There is no receiver/drier or other filter in the system to
protect the rear TXV. If a filter is not installed, the rear TXV may become restricted shortly after the
repair.
2002 - 2004 Honda CR-V - Compressor Failure
These vehicles use a low mounted scroll design compressor
that is prone to failure. Scroll type compressors are
particularly sensitive to both liquid slugging and lack of
lubrication.
Honda TSB 09-076 indicates that if evidence of debris is
found in the suction line at the inlet to the compressor, then
every component in the refrigerant path should be replaced – compressor, condenser, drier, evaporator,
all lines and hoses and the TXV.
This solution may not always be practical for many consumers. However, for a successful lasting repair,
certain parts must be changed and procedures followed carefully.
Note: When scroll compressors fail, they produce a lot of debris, which will be distributed throughout
the AC system. At a minimum, the compressor and the condenser/receiver drier must be changed.
Inspect the TXV inlet for debris and or contaminated oil. If evidence of either is found the TXV valve

28
should be replaced. All other components not being replaced should be thoroughly flushed including the
evaporator. Refer to the section on flushing for special tips and tools on effective flushing.
Note About Honda Condensers
These systems are very finely balanced. This system only uses 18oz of refrigerant. For the system to
cool properly, every component must operate at maximum efficiency. It is not enough for the
replacement condenser to “look similar” to the unit being removed. It must also have the same heat
exchange efficiency. Compare the overall size, tube count and the fin density of the replacement
condenser with the old unit – they should be a close match.
2006 - 2008 Honda CR-V and Civics – AC Performance Issue
Affected Models
2006 – 2008 Civic with automatic transmission and all 2007 - 2008 CR-Vs
The customer concern is usually a momentary drop off in AC performance under hard acceleration from
below 20 mph. The problem is that the PCM is disengaging the compressor too soon on acceleration.
Honda has issued a flash update to address this concern in TSB # 07-062. However, the TSB points out
that compressor disengagement is normal under hard acceleration and that the symptom may not be
completely eliminated by the calibration update.
Dodge Trucks - Late 1990s – Early 2000s
The Customer Concern
Occasionally, the AC starts blowing warm air. The
problem can be very intermittent – it may only occur on
longer trips or during stop/go traffic. This can make it
particularly difficult to diagnose. There are no diagnostic
trouble codes set.
The compressor clutch coil may be going open circuit
intermittently. The clutch coils on some of these compressors
have a higher than normal failure rate. The coil potting
material cracks and exposes the coil winding leading to failure.
One way to confirm the diagnosis is to monitor the voltage
across the clutch with a DMM or oscilloscope and wait for the
problem to occur. If the compressor stops turning but full
system voltage is still available then it is probably a failing
clutch coil. Compare the resistance of the clutch coil before
and after the problem occurs. Also, check the air gap. An
excessive gap can also cause intermittent clutch engagement.
Excess Heat has Cracked the
Potting and Exposed the
Clutch Coil Winding Causing
Premature Failure of the Coil

29
SERVICE PROCEDURES
Essential Steps for Successful Compressor Replacement
1. Replace the Accumulator or Receiver/Drier
• To maintain the compressor warranty, the drier must be
replaced during installation of replacement parts.
2. Replace The Orifice Tube/Liquid Line
• The orifice tube is the main filter in a CCOT system. If
it is not replaced, the replacement compressor will not
be lubricated properly and will fail. Some orifice tube
systems have the tube crimped into the liquid line. The
liquid line must be replaced or an orifice tube repair kit
installed to prevent compressor failure and poor system
performance.
3. Inspect/Replace the Thermostatic Expansion Valve (if equipped)
• TXV inlets must be checked for debris or metal particles. Any
restrictions will lead to poor performance or compressor failure.
4. Flush the System With Approved Flush
• When the system is repaired, every inch of the refrigerant path
should be either new or flushed. Oil acts like fly paper. It will trap
and hold metal debris - particularly in the evaporator. Removal of
all dirty oil and debris is essential to avoid repeat compressor failure. Newer condenser
designs are difficult, if not impossible to thoroughly clean, and in many cases must be
replaced.
5. Add the Correct Type and Amount of Oil
• Oil is the lifeblood of an A/C system. Running the compressor without adequate
lubrication for even a short while will cause catastrophic damage. Unless instructed
otherwise by the compressor instruction sheet, add half the oil charge to the compressor.
On orifice tube systems, add the other half of the oil charge to the accumulator. On TXV
systems add the other half to the evaporator. Check that you are using the correct:
• Oil type: PAG, Ester or Mineral
• Amount
• Viscosity
6. Check Compressor Clutch Air Gap Before Installation
• The air gap is preset at the factory; however, it is a good
practice to double check it before mounting the unit. Incorrect
air gap will cause poor performance or noisy operation. Air
gap specs are on the instruction sheet. Check the gap at three
points around the clutch.
Replace Receiver
Drier, Accumulator &
Orifice Tube
Thermal
Expansion
Valve (TXV)

30
7. Proper Evacuation Time
• The A/C system must be free of moisture and air to work properly. Single evaporator
systems should be evacuated for at least 45 minutes and dual evaporator systems for at
least 90 minutes. Longer evacuations produce colder duct temperatures. A warm engine
or sun-load on the vehicle will evacuation.
8. Correct Refrigerant Type and Amount
• Either R-12 or R-l34a should be the only refrigerants used to maintain system integrity
and warranty. The correct amount of charge is critical for proper performance. Too little
and there will not be enough liquid refrigerant to carry the oil around the system; too
much will slug the compressor causing irreparable damage.
9. Before First Start-up, Hand-turn The Compressor Shaft at least 15 Times with the Hose
Assembly Installed
• Oil and liquid refrigerant cannot be
compressed. Hand turning the
compressor shaft will clear oil and
refrigerant from the compression
area and reed valves.
10. Burnish The Clutch Assembly
• This process will increase the grip
between the clutch hub and the
clutch pulley and enhance system
performance. With the engine @
2000 rpm, cycle the compressor
clutch off and on twenty times
using the A/C control switch on the
dash
11. Clutch Electrical Circuit Tests
• Perform a voltage-drop test at the compressor clutch with the clutch engaged. Available
voltage should be within 1.5V of system
voltage but never less than 12V. It is always a
good practice to perform a vehicle charging
system test including a battery load test as
part of this procedure.
12. Proper Air Flow Through The Condenser And
Radiator
• Inadequate airflow through the condenser and
radiator will cause excessive discharge
pressures, poor performance, and compressor
or clutch failure. Always clean the condenser
Check Fan Clutch Operation –
Bearing Play, Seal Leaks
Turn Compressor at Least 15 Times
by Hand Before Start-up – Use
Compressor Turning Tool

31
and radiator, check the cooling fan or fan clutch, check for air dams and radiator seals.
Check between the radiator and condenser for debris. Check the coolant level in the
radiator, as well as the radiator cap for pressure range and sealing.
13. Check for Leaks
• Use an electronic leak detector or fluorescent dye to check for leaks. A leak will cause
system failure. A job that was performed perfectly in every other way can still come back
with a failed compressor if a leak goes undetected. When the refrigerant level falls too
low, there will not be enough liquid refrigerant to carry the oil around in the system and
maintain compressor lubrication.
14. Verify the Repair
• Finally, when all repairs are completed, confirm the overall
integrity and efficiency of the system by performing a
“Maximum Heat Load Temperature Test” as described on
page 63. This will help you confirm that there are no
underlying weakness in the system that have not been detected
before you return the vehicle to the customer.
DMM with Contact
Temperature Probe

32
Lubrication
Oil is the lifeblood of the AC system. Without proper lubrication, the compressor will fail quickly.
R134a and PAG oil do not mix well. Maintaining lubrication in an R134a system is more difficult than it
was in old R12 systems. R12 and mineral oil mixed and bonded much more easily. Even in a gaseous
state, R12 still carried some oil back to the compressor.
In an R134a system, the oil is carried around the system by the liquid refrigerant. Refrigerant enters the
evaporator as a liquid and evaporates as it passes through the evaporator. As the refrigerant evaporates,
the oil tends to drop out. If the refrigerant charge level drops too low, there is not be enough liquid
refrigerant remaining to carry the oil up and out of the evaporator and back to the compressor. The oil
drops out and pools in the bottom of the evaporator. The compressor starves for oil and fails rapidly. For
this reason exact system charge level is critical for proper lubrication. Cycling Clutch Orifice Tube
(CCOT) Systems are particularly sensitive to undercharging.
Adding Oil
• Add the specified capacity, type and viscosity of oil. Confirm this information from several
sources if possible.
• When performing any major service work, all of the oil should be removed from the system.
Remove the compressor and accumulator / receiver drier and drain all the oil. Remove the oil
from the evaporator and condenser by flushing with the proper solvent, tool and technique (read
the section on flushing page 43).
Note: Multi-pass condensers should only be flushed to remove oil. If the compressor has suffered
catastrophic failure these condensers cannot be flushed. They should be replaced (refer to the section on
flushing).
• Add half of the oil charge to the compressor and half to the accumulator or other components.
• Most remanufactured compressors do not contain a full oil charge. The complete amount of
specified oil must be added to the compressor through the suction port or oil plug before
installing it on the vehicle.
• Rotate the compressor shaft by hand at least fifteen times after all the hoses are attached but
before the engine is started. This moves the oil out of the compressor to avoid liquid slugging on
start up.
• The old method of “Oil Balancing” to determine the proper amount of oil is extremely
inaccurate. There are way too many variables and unknown factors. The system should be
flushed and a complete system charge of oil installed.
About Oils
There are many different types of refrigerant oils in the Market, today. Mineral based to synthetic
blends are available with various viscosity ranges. Mineral, parafinic, Ester, and PAG oils have been
designed with certain characteristics that each compressor manufacturer has determined, through testing,
to provide the best lubrication. The table following lists the type and viscosity of each oil recommended
by each compressor manufacturer.

33
Compressor Manufacturer And Type Oil Type and Grade for R134a Systems and
Those Retrofitted From R12
Special Notes: Virtually all R12 systems used Mineral/500 oil. Ford used a parifinic oil in the FS6
with R12. GM used a special Retrofit oil when retrofitting a V5 compressor from R12 to R134a and
when not replacing the V5 compressor.
Behr / Bosch Rotary Type (Make sure
Comp will handle 134a)
PAG 46
Behr / Bosch Piston Type (Make sure Comp
will handle 134a)
PAG 46
Calsonic V5 PAG 150
Calsonic V6 PAG 46
Chrysler RV2 PAG 46
Chrysler C171, A590, 6C17 PAG 46
Diesel Kiki / Zexel DKS, DKV, DCW PAG46
Ford FS6, FX15, FS10, FS20, 10P,
10PA, HS15, HS17,
HS18, E6DH, Scroll
PAG 46
General Motors Harrison A6, R4, DA6, HR6,
HT, V5, V7, HU,
PAG 150
General Motors CVC, Nippondenso and Nipp.
Replacements
PAG 46
Hatachi PAG 46
Keihin (NOTE: Some Keihin compressors are
not recommended to be retrofitted to R134a)
PAG 46
Matsushita FX80, FX105 PAG 100
Matsushita NL Series PAG 100
Nihon Be sure the compressor will
handle R134a
PAG 46
Nippondenso 6P, 10p, 10PA, 10PO8E,
SP127, SP134, 6E171
10S17, 10S20, 6C17,
6CA176, VS16N
PAG 46
Nippondenso TV PAG 100
Panasonic PAG 46
Sanden SD500 Series, SD700 Series PAG 100
Sanden SDV710, SDB Series, TV, TRS PAG 46
Seiko-Seiki PAG 100
York / Tecumseh PAG 46
All Brands of High Voltage Compressors HV Ester

34
Refrigerant Recovery, Recycling and Recharging
Important Note about System Charge Level: We cannot
overemphasize the importance of system charge level.
Refrigerant charge capacities have been reduced
dramatically over the years. Modern systems are designed
to provide the same level of cooling with ever-smaller
refrigerant amounts. The consequences of even an ounce or
two over or undercharged can be catastrophic. It is vital to
get the refrigerant charge level exactly right to avoid an
expensive comeback.
Undercharged
R134a does not dissolve in PAG or POE oil. In an R134a
system, the oil is carried around the system by the liquid
refrigerant. Refrigerant enters the evaporator as a liquid and evaporates as it passes through the
evaporator. As the refrigerant evaporates, the oil tends to separate out. If the refrigerant charge level
drops too low, all the liquid refrigerant evaporates near the bottom of the evaporator. Now there is not
enough liquid refrigerant to carry the oil up and out of the evaporator and back to the compressor. The
oil drops out of circulation and pools in the bottom of the evaporator. The compressor starves for oil and
fails rapidly. All systems will fail from lack of lubrication but Cycling Clutch Orifice Tube (CCOT)
Systems are particularly sensitive to undercharging.
Overcharged
On the other hand, an overcharged system can have equally
serious consequences. Liquid refrigerant may exit the
evaporator and slug the compressor. Since a liquid cannot be
compressed, serious damage to the compressor can result. It
is not unusual to see a compressor case cracked open due to
liquid slugging. TXV systems are particularly sensitive to
overcharging since there is no accumulator to allow the
refrigerant to evaporate before reaching the compressor.
Note: Several manufacturers have TSBs advising of revised
refrigerant and oil capacities for some of their vehicles in an
attempt to combat premature compressor failure.
This Scroll Compressor Failed From
Lack of Lubrication – The Scroll &
Rotor Are Completely Dry
Cracked Case from Liquid
Slugging

35
Recovery
Refrigerant recovery is important for several reasons:
1. It Is Required by Law
R134a and R12 are considered “greenhouse gasses” that contribute to global warming. It is
illegal to vent them to the atmosphere. R12 is also an ozone depleter. These refrigerants (and
others) must be recovered and appropriately processed using approved recovery/recycling
equipment.
2. System Charge Level
If you are performing a normal maintenance AC service to recover, evacuate and recharge the
system (without opening it up), then you need to be certain that:
• All the refrigerant has been completely removed from the system before
recharging it.
• The amount you charge back is exactly the specified amount the system calls for.
Average system capacity has been reduced dramatically over the past 10 to 15 years. Today,
system capacities of 12 to 16 ounces (oz.) are common. A few systems are even less than that. If
a recovery machine failed to recover 2 oz. from a 12 oz. system and the shop tried to short
circuit the service process by going straight from recovery to recharge (without evacuation) a
serious overcharge could occur. When the system is charged with the specified 12 oz. it would
be about 16% overcharged. Compressor slugging with catastrophic damage could occur.
Note: This scenario would only happen in the event that the evacuation part of the service was
bypassed – in other words if you went straight from recovery to recharging without evacuating
the system. Modern recovery/recycling /recharging equipment will not allow transition from
recovery to recharging when in automatic mode.
Several years ago, the Society of Automotive Engineers (SAE) recognized that existing
standards for refrigerant recovery equipment were not precise enough to meet the recovery and
charge accuracy requirements of newer vehicles with reduced charge capacities. Studies had
shown that older equipment could leave up to 30% of the refrigerant in the system during a
normal recovery operation. SAE developed a new standard, J2788, for
recovery/recycling/recharging equipment to meet the more exacting recovery and recharging
needs of reduced capacity systems. A recovery/recycling/recharging machine meeting the J2788
standard (J2810 for recovery only equipment) must recover at least 95% of the refrigerant
charge in 30 minutes or less at 70-75°F ambient.
3. Quality of Recovered Refrigerant
Recovered refrigerant must be sufficiently pure and free of contamination so that it will not
affect system performance or longevity when reused. Air, particulates, old oil and other
contaminants must be removed. The key to maintaining high quality recovered refrigerant is
proper equipment maintenance and vigilance.

36
Recovered Refrigerant - Contamination
Sealer Contamination
Before connecting any equipment to a vehicle that you are unfamiliar with,
use a sealer identifier to check for the presence of sealer. Undetected sealer
can ruin your refrigerant identifier, recovery/recycling/recharging
equipment, recovered refrigerant and contaminate the next vehicles you
service. Most sealers depend on the presence of either air or moisture to
work – neither of which you want in an AC system. Eventually sealers
coagulate throughout the system. Repairing a sealer-contaminated system
will usually require replacing every component in the refrigerant path.
Sealer cannot be flushed.
Air Contamination
Air is a non-condensable gas at the
temperatures and pressures found in an
automotive AC system. It remains in
gaseous form throughout the system and
takes up valuable heat exchange real estate
in both the condenser and evaporator. This
reduces system performance and puts
additional strain on the compressor by
raising system pressures. Compressor noise
is often caused by air in the system. Air
also supports corrosion and chemical
deterioration in the system over time. This
can lead to leaks and other component
failures.
During both recovery and evacuation, the
AC system and the recovery/evacuation
equipment are under vacuum. Inevitably,
air will find its way into recovered
refrigerant unless preventative measures are
taken. Keeping air out of recovered
refrigerant is like trying to keep sand out of
a beach house!
Note: Most recovery/recycling/recharging
machines have an automatic air-purge
function. However, this feature has
limitations. To check for air content these machines compare the actual pressure in the tank of recovered
refrigerant with what the pressure would be in a tank of virgin refrigerant at that temperature. If air is
present, the pressure in the recovered refrigerant will be higher. The auto air-purge function bleeds off
Sealer Detection Tool
Use an Air Contamination Gauge Set Attached to the
Recovery Tank Vapor Port to Confirm that Recovered
Refrigerant is Free of Air. At a Stabilized
Temperature, the Two Gauges Should Indicate the
Same Pressure. The Top Gauge Reads Actual Tank
Pressure, the Bottom Gauge Indicates what the
Pressure Would be in a Tank of Virgin Refrigerant. If
the Pressure on the Top Gauge is Higher that the
Bottom Gauge then the Refrigerant Contains Air.
Open the Vapor Valve Periodically Until the Two
Gauges Read the Same Pressure. It Can Take Up to
48 Hours to Completely Vent All the Air.

37
pressure in the recovery tank until the pressure in the tank is close to what it would be in a tank of pure
R134a.
However, the EPA is concerned that refrigerant should not be vented to the atmosphere. They have set
standards for “acceptable air contamination in reclaimed refrigerant.” The EPA considers 2% air
contamination acceptable. Compare the pressure/temperature relationship chart on page 93 for virgin
R134/R12 with the “acceptable” air contamination pressure/temperature chart for “Reclaimed
Refrigerant Contamination” on page 94. Note that at a given temperature, the acceptable pressure in a
tank of reclaimed R134a (or R12) is several PSI higher than it would be in a tank of pure refrigerant at
the same temperature. Therefore, to avoid any possibility of venting refrigerant to the atmosphere,
recovery machines typically only vent down to the higher pressure on the “Reclaimed Refrigerant
Contamination” chart. In effect, this means that there could be up to 2% air in your recovered
refrigerant.
The other concern with auto air-purge is time. It can take up to 48 hours for the trapped air in recovered
refrigerant to outgas completely. As the auto air-purge function vents the recovery tank pressure down to
the “acceptable” level, additional air will start to outgas from the refrigerant and pressure will start to
build up again. It can take up to 48 hours for all the air to outgas completely from a tank of recovered
refrigerant as the air-purge function goes through successive venting cycles. In a busy shop
environment, as equipment is moved from one vehicle to the next, there simply is not enough time for
the auto-air-purge function to vent all the air.
One solution to this issue is to use two recovery
tanks. Use one tank for recovery only until it is full.
Leave the machine on to allow the auto-purge
feature time to vent the air. When the tank is full
replace it with an empty one. Now use the stabilized
tank of recovered refrigerant with a separate
charging cylinder or scales for charging.
Rogue Refrigerant
Use a refrigerant identifier to confirm that the
vehicle you are about to recover from is not
contaminated with a rogue refrigerant. Use of
refrigerants other than R12 or R134a will void your
compressor warranty. A wide variety of problems
can arise with the use of other refrigerants.
• They may be flammable.
• Blended refrigerants can be unstable and separate into their component parts. The different
constituents may leak at different rates over time (due to different molecular sizes) causing the
refrigerant to perform unpredictably.
• They may attack materials in the system.
• The pressure/temperature profile will be different from R134a or R12, making diagnosis
difficult.
Recovery Recycling Only Machine

38
Recovery Quick Tips
Following are some tips to help you ensure that all the refrigerant is completely recovered from the
system and that your recovered refrigerant remains free of contamination:
• Maintain equipment. Perform the manufactures recommended maintenance service on schedule. Pay
particular attention to the quick disconnect service couplings. They are a common source of leaks
that are not always obvious - they may hold pressure but not vacuum. They are complex components
with quite a number of internal parts, including several seals and springs. They are high wear items
as they are repeatedly connected and disconnected from the system under pressure. Replace your
machines filter regularly. J2788 machines track filter life and lock the machine down when filter is
used up.
• Use Heat. Heat has a dramatic effect on the rate of refrigerant recovery from a system. Servicing air
–conditioning when the ambient temperature is low, increases the length of time it takes to recover
refrigerant from the system. In addition, as recovery begins and refrigerant starts to evaporate, it
absorbs heat from its surroundings due to the latent heat of evaporation effect. This slows the
recovery process even further. This is why the accumulator or receiver drier feels cold to the touch
during recovery. If the drier still feels cold after recovery is apparently complete, then you know that
all the refrigerant has not been removed from the system. Carefully warming the drier with a heat
gun will accelerate the recovery process.
For rapid recovery, set the AC system on MAX heat and recirculate with the hood lowered. This will
warm all the underhood AC components and the evaporator.
Note: If the vehicle uses an electronic variable displacement clutchless compressor (see page 14) do not
run the engine during recovery or if the system is low on refrigerant or oil. The compressor turns all the
time the engine is running and could be damaged from lack of lubrication.
• Periodically use your refrigerant identifier to check for air in your refrigerant recovery tank and also
in vehicles you have just recharged.
• After the vehicle is
repaired, use tamper
resistant shrink-on or tie-
wrap system guards to
seal the service ports. If
the vehicle returns to you
for service and the system
guards are missing or have
been tampered with, you
know the system may
have been worked on
since you serviced it. Shrink-on or Strap-on System Guards Help to Deter Tampering

39
System Evacuation
A thorough evacuation produces colder duct temperatures. System evacuation is necessary to remove all
air and moisture from the AC system. Air is a non-condensable gas (NCG). It remains in a gaseous state
throughout the AC system and takes up valuable heat exchange real estate in both the condenser and
evaporator. This reduces system efficiency. It also raises system head pressure, which increases
compressor stress and noise. Air also holds moisture, which creates additional problems.
Moisture creates immediate and long-term effects in the AC system. In the short term, it freezes at the
expansion device, impeding refrigerant flow and reducing performance. As the moisture freezes,
refrigerant flow is reduced and the system starts to blow warm. Now the moisture starts to thaw and
refrigerant flow increases. The cycle starts over again. Cycling back and forth from cold to warm is a
strong indication that there is moisture contamination in the system. Moisture also holds dissolved
oxygen, which can support the creation of acids and corrosive chemical activity over time. Corrosion
eventually causes leaks as it eats through the thin heat exchange surfaces of the evaporator and
condenser. Corrosion debris can restrict the expansion device and damage the compressor.
Following a good evacuation procedure will remove the
maximum amount of air and moisture from the system.
However, there are no real shortcuts. Removing moisture from
the system takes time. Moisture is removed by literally boiling
it from the system. The only way to get water to boil at shop
temperature is to reduce the pressure on it.
The two keys to rapid, effective evacuation are a deep vacuum
and heat. Refer to the “Boiling Point of Water at Specific
Inches of Vacuum” chart on page 96. Note that vacuum must
reach 29.4 inches of mercury (inHg) before water will boil at
60°F. If you are evacuating a system on a 60°F day and the
needle on the low side gauge is pointing at 29 inHg exactly,
then you are not removing any moisture from the system. 29
inHg “looks” good, but it is not enough on a 60°F day.
Referring to the chart again, we can see that on an 80°F
day, 29 inHg would be enough to evacuate the system
eventually. However, a combination of both deep
vacuum and heat are the key to rapid evacuation.
The low side gauge on a standard air-conditioning
gauge set is not an accurate enough tool for assessing
true vacuum. Differentiating between 29 inHg and 29.4
inHg is barely the width of the needle. A micron
vacuum gauge is a much more accurate tool. For
example, on a micron vacuum gauge, 29.14 inHg reads
as 20,000 microns while 29.89 inHg reads as 750
microns – small changes in vacuum become much more
obvious.
Vacuum “Looks” Good at 29” –
But on a 60°F Day Not Good
Enough – Must to be 29.4”
Use a Micron Vacuum Gauge to
Measure True Evacuation Vacuum

40
To use the micron gauge, tee it into one of the service hoses as close to one of the vehicles service ports
as possible. An ideal vacuum for automotive air-conditioning is less than 500 microns but below 750
microns is acceptable.
The key to achieving a deep vacuum is maintaining
equipment. This means changing the vacuum pump oil
frequently at the manufacturers recommended intervals.
This is usually based on hours used and could mean every
couple of weeks during a hot humid AC season. The other
weak point in evacuation equipment is usually the service
hose quick-disconnect couplings. They undergo a lot of
wear and tear as they are continuously connected and
disconnected to each system. Inevitably, they develop
leaks. Leaks are not always obvious as they may only
occur under vacuum and not under pressure. The
couplings should be serviced or replaced regularly.
Evacuation Time
Single evaporator systems should be evacuated for at least 45 minutes and dual evaporator system for at
least 90 minutes.
Evacuation Quick Tips
• Maintain evacuation equipment.
• Regularly validate the ability of your vacuum pump to
pull a deep vacuum with a micron vacuum gauge.
• Use heat – warm all the air-conditioning components
on the vehicle by running the engine with the hood
lowered. Also, run the heater on max recirculate with
the blower on high. This will warm the evaporator.
Warming all the AC components dramatically
accelerates both refrigerant recovery and system
evacuation.
Note: If the system uses a clutchless compressor,
(where the compressor shaft turns all the time) do not
run the engine without refrigerant or oil in the system.
Moisture Contaminated Vacuum Pump
Oil after Just a Few Hours of Service
Change Vacuum Pump Oil at
Recommended Intervals

41
System Charging
Exact charge level is critical – refer to the note about system charge level and the consequences of under
or overcharging on page 33. System undercharging causes lack of compressor lubrication and
overcharging causes compressor slugging. In either case, catastrophic consequences can result. With
many system capacities now less than 1lb, old charging methods and equipment can easily result in a
gross under or overcharge. Just a two-ounce undercharge on a thirteen-ounce system (e.g. some Honda
Fits) amounts to a 15% error – enough to cause lubrication issues.
Older equipment can be off by as much as 3 to 4 ounces on charge amount. In addition, most older
equipment does not compensate for the refrigerant that remains in the hoses after charging. This can be
significant – up to about one ounce per foot of hose.
Charging Quick Tips
• Use Recovery/Recycling/Recharging equipment that meets SAE J2788 specifications (see page
12). These machines are much more accurate than previous equipment and are specially designed
to take account of the reduced charge capacities of newer vehicles. They can be programmed for
the specific hose length being used on the machine.
• Consider using a charging cylinder
or electronic scale for charging.
These are very accurate methods.
Another advantage of using separate
equipment is that you can improve
shop productivity. By using separate
Recovery/Recycling/Recharging
equipment, you can service three
vehicles simultaneously.
• Verify and calibrate electronic
charging scales with a known
weight every week during peak AC
season.
• Service hoses that have been pulled
into a vacuum during evacuation can
hold four to six ounces of
refrigerant, depending upon hose
length and manifold design. J2788 compliant equipment automatically compensates for
refrigerant trapped in the hoses. However if you are using older equipment or a separate charging
scales or cylinder with a manifold gauge set, then you should manually compensate for the
refrigerant that remains in the hoses after normal charging. There are two ways to do this.
1. Add about one ounce per foot of service hose to the specified charge amount. If the
system specification was 20 oz. and your service hoses were four feet long, then you
would set your charging machine to charge 24 oz. of refrigerant to compensate for the
four oz. that would remain in the hoses.
Use a Charging Cylinder For Improved Charge
Accuracy

42
2. An alternative method is to draw any refrigerant remaining in the hoses into the system
after the initial charge is complete. Disconnect the high side service hose from the
system. Leave the low side connected. Open the high and low side manifold valves and
run the engine with the AC on. This will draw any refrigerant remaining in the entire
service hose and gauge assembly into the low side of the system. At low side pressure (30
– 40 PSI) all the refrigerant in the hoses swill be in a gaseous state. There will be
virtually no refrigerant remaining in the hoses.
• Let the system stabilize for several minutes before engaging the compressor clutch if liquid
refrigerant has been installed in the high side. This will eliminate the possibility of slugging the
compressor and breaking a piston or reed valve.
• Charging by individual cans will usually lead to an undercharged condition due to the refrigerant
loss that occurs when each can is change. There will always be residual refrigerant left in each
can. It’s only a guess, as to how much refrigerant was in the can to begin with. The other
question is, how do you determine the contents of a partial used can? Another issue to contend
with is the introduction of air into the system. Air can enter through the service hose as the cans
are changed.

43
Flushing
Note: When a system has suffered a
catastrophic compressor failure, it is essential
that when the repair is complete, every inch of
the refrigerant path is either new or flushed –
this includes the evaporator.
Flushing – Why Is It Necessary?
• To remove the failed compressor’s
debris from any components that are
not being replaced.
• To remove dirty oil from the system –
especially from the evaporator.
A Successful Flush Requires:
1. A high quality flush solvent. A good
solvent should have the following properties:
• Be effective at removing oil
and debris.
• It must evaporate rapidly.
Any residue remaining in
the system can affect system
performance and cause
chemical deterioration in the
system over time.
• Be chemically stable. It
must not react with or attack
materials in the system.
• Be safe. Have low
flammability and not be a
health hazard.
Products such as brake cleaner, de-
greasers, carburetor cleaners, denatured
alcohol, etc should not be used as flushing
agents.
2. An effective flushing tool or machine. A good flush tool should propel the flush solvent
through the component being flushed and maintain the solvent momentum throughout the flush
process. When all the flush solvent is dispensed, it should be possible to transition from flush to
air-purge without allowing airflow through the component to stop. This prevents the flush
solvent from “dropping out” inside the evaporator (or other component). Even a small amount of
residual solvent or dirty oil can cause rapid failure of the replacement compressor. The tool
shown in figure 2. meets these requirements by using an air pressure regulator, a shut off valve
and a universal adapter. The adapter enables a fixed connection to the component to be made.
Schrader Valve – Uses
Static Air Pressure. No
Momentum
Figure 1
Ineffective Flush Tool – Uses Static Air
Pressure. Cannot be Attached to Component
Rubber Tip Cannot
Be Attached to Component
Air Pressure
Regulator
Universal
Adapter
Figure 2
Effective Flush Tool
(Shown With Evaporator
Removed from Vehicle
for Clarity)
Shut-off Valve
To Capture
Container

44
This allows air-purge through the component to be continued for 30 minutes after all the flush
solvent is dispensed. Air-purge is necessary to ensure that all solvent and oil residue are
completely removed. The upgraded flush tool should be available from your parts store. A good
flush simply cannot be achieved with the tool shown in figure 1. on the previous page. The static
air charge in the can runs out before all the solvent is dispelled. The rubber tipped air blower
must be manually held to the component during the flush process – not very practical. The use of
a tool like this will result in a contaminated soup of dirty oil and solvent being trapped in the
evaporator.
The very best flush results are obtained with a professional closed
loop flush machine similar to the one shown here in figure 3.
These machines allow the use of a greater volume of solvent, are
usually flow reversible and have a pulsing action to dislodge
trapped debris.
3. A Proper Flushing Technique. A good flushing process requires
using a quality solvent and flushing tool in accordance with the
manufactures instructions. For example, if you are using a tool
similar to the one shown in figure 2, you will need to ensure that a
constant supply of dry shop air or nitrogen is supplied to the flush
can. Meter about a third of the flush solvent into the evaporator
and allow it to soak for 10-15 minutes. Complete the flush at 40
PSI. When all the solvent is expelled from the can, raise the air
pressure up to 80 PSI and continue to purge air through the
component for an additional 30 minutes to dry out any residue of
solvent or oil.
Quick Tips
• Flat tube, multi-pass condensers
cannot be flushed – they should be
replaced. The internal tubes are
extremely small. The image on the
right shows a cross-section of early
and late design condenser flat tubes
(a penny is sandwiched in-between
for size reference). The bottom
tube is typical of R134a condensers
until the mid 2000s. The top cross-
section is the very latest design. In
addition, the condenser header
tanks at each end are dammed in
several places forcing the
refrigerant to follow a circuitous path through the condenser – flush solvent would have to
follow a similar path.
Figure 3
Professional Closed
Loop Flush Machine
The Internal Passages of Flat Tube Multi-pass,
Condensers Are Extremely Small. They Are
Impossible to Flush After a Catastrophic Compressor
Failure. Top Sample is the latest design.

45
• Hoses and lines with
inline filters or
mufflers cannot be
flushed – they should
be replaced.
Accumulators and
receiver/driers also
cannot be flushed.
They have convoluted
internal passageways
and contain the
system desiccant – the
desiccant will
disintegrate on
contact with flush
solvent.
• It is usually more
effective to flush
components
individually. Trying
to flush the entire
system at once, or
large sections of it, can result in debris being distributed to other areas of the system.
Important Note: Most compressors fail from lack of lubrication. All air-conditioning systems leak
refrigerant gradually over time. Eventually there is not enough liquid refrigerant in the system to carry
the lubrication oil up and out of the evaporator and back to the compressor. The oil drops out of
circulation and pools in the bottom of the evaporator. The compressor eventually fails.
In the weeks and months leading up to the final failure, very fine metal particles slough off the
compressor cylinder walls and pistons. These fine particles are carried throughout the system. Some will
even pass through the tiny passages in the orifice tube and TXV valve. They are finally trapped in the
oil, which has been pooling in the bottom of the evaporator. There they form a contaminated soup of
dirty oil and abrasive particles. Think valve-grinding compound! It is critical that this dirty oil is
completely flushed from the system before the compressor is replaced. If it is not, premature failure of
the replacement compressor is inevitable.
This pooled oil in the evaporator can amount to several ounces and cause additional problems. If the
compressor has failed several times already, and the old oil was not removed after each failure, the result
can be a gross overcharge of oil as new oil is added with each compressor replacement. In addition to
the abrasive damage, the compressor can also be slugged by this excess of oil. Furthermore, the excess
of oil coats the heat exchange surfaces of the evaporator and condenser reducing their efficiency.
Accumulators and Receiver
Driers Have Convoluted
Internal Passages. They Also
Contain Desiccant Which
Disintegrates on Contact with
Flush Solvent
Receiver Drier Cutaway
Lines with Inline Filters and
Mufflers Cannot be Flushed
Note Pinhole that Refrigerant
Must Pass Through
Accumulator Cutaway

46
Leak Checking
Hard to find refrigerant leaks are one of the more exasperating aspects of air-conditioning service and
repair. A vehicle is brought to you with a complaint of poor performance. You recover, evacuate and
recharge the system and it performs perfectly. You know the system was low on refrigerant when it
came in yet you cannot find a leak. Or, you repair a system and it comes back after a week, a month or
even a year and you find that it’s low on refrigerant. Yet despite your best efforts, you cannot find the
leak.
With the continuing trend toward ever-smaller system refrigerant capacities, the same leak results in a
system performance issue much more quickly than before. Being able to find small leaks has never been
more important.
Before you begin, look the system over carefully for obvious signs of a leak. On an R134a system, oil
does not always show up at the site of a leak because it does not mix well with the refrigerant. However
depending on the location and the size of the leak, there may still be some oily residue at the leak site.
In this section, we will discuss the various methods of refrigerant leak detection including some new
ones. We will also provide some tips that should make leak detection easier and more reliable,
regardless of which method you use.
Electronic Leak Detection
Electronic leak detection is probably the most common method of leak detection. It is certainly the
easiest and fastest to perform. However, it can be unreliable and ineffective if you do not follow a good
procedure. Here are some tips for a better electronic leak detection experience:
• There must be some refrigerant in the system – at least 50 PSI. Electronic leak checking in colder
weather will be less successful.
• Perform the leak check with the engine off. Stop all airflow across the vehicle. This is extremely
important. Ideally, perform the leak check indoors with all shop fans and ventilation shut off.
This will greatly increase your success rate with electronic leak detection.
• Conduct the leak-check methodically by working your way across each section of the system.
Move the probe tip at about one to two inches per second about ¼-inch from the surface of the
line or component being checked. Verify an apparent leak at least once by blowing shop air into
the area of the suspected leak, and repeating the check of the area. In cases of very large leaks,
blowing out the area with shop air can help locate the exact position of the leak.
• Oil will mask leaks. Allow the vehicle to sit for several hours before performing the leak check.
This allows the oil to drain down in the system and expose leaks. However, to check for leaks in
the very bottom of the evaporator it may be helpful to check a few minutes after system shut
down before all the oil has drained down and obscured the leak.
• While waiting to perform the leak-check, park the vehicle outside in direct sunlight. This raises
low side pressure and improves your success rate in finding evaporator leaks. If you need to
bring the vehicle inside to complete the leak-check, do NOT run the AC system or the blower

47
motor. You do not want to stir up the oil or vent the evaporator case before you perform the leak-
check.
• To raise static pressure in the system during colder weather, run the engine with the AC off but
with the system set on max heat recirculate. This will warm the evaporator. Turn the engine off
before performing the leak check. If you suspect an evaporator leak, wait 10 or 15 minutes to
allow some refrigerant vapors to build up in the evaporator case.
• Refrigerant is heavier than air. When leak checking the evaporator, try to get the detector tip into
the bottom of the evaporator case. Removing the blower resistor block or other easily accessible
component from the side of the evaporator case may improve access. Also, check at the
evaporator drain. Alternatively, position the detector tip in the dash vent closest to the evaporator
and turn the blower on for just a second or two. This may waft refrigerant vapors by the tip of the
probe and confirm the leak.
• Use a detector that meets the latest SAE specification. SAE J2791 for R134a electronic leak
detectors was issued a few years ago (see page 13). These detectors are more accurate and robust
than earlier models and less sensitive to false triggering.
Note: SAE J2913 has just been issued for electronic leak detectors designed to work with the
new refrigerant R-1234yf. Some new detectors meet both specifications and will detect both
R134a and R-1234yf. See pages 11 and 13.
• There may be two or more leaks! After you find and mark the first one, complete your normal
routine for checking the entire system.
• Maintain the detector by cleaning and replacing the tip filter per the manufacturer’s instructions.
• Compressor front seal leaks can be difficult
to confirm. Try removing the belt and
placing a shower cap over the compressor
clutch and nose. Wait several minutes and
slip the detector tip into the shower cap
toward the bottom of the compressor. If it
triggers, suspect a compressor front seal
leak.
Remove the Belt and Place a Shower Cap
Over the Compressor Nose. Insert the
Detector Tip into the Cap Near the Bottom of
the Compressor to Check for Leaks

48
Hydrogen Trace Gas Leak Detection
A new leak detection method
called “Hydrogen Trace Gas Leak
Detection”, has recently become
available. The technique is not
new, but is just now being used
for automotive AC system leak
checking.
The technique uses an electronic
leak detector that detects the
presence of hydrogen instead of
refrigerant. Hydrogen is the
smallest and lightest discrete
particle with an atomic number of
one. It is the first element on the
periodic table. The H2 molecule is many times smaller than the complex R134a molecule. This makes it
very effective at ferreting out even the smallest leaks.
A gas cylinder with a mix of 5% Hydrogen and 95% Nitrogen is used to charge the AC system to about
30 PSI. Although hydrogen gas is extremley flamable, it is safe at this 5% concentration in the nitrogen.
The gas mix is available from many welding supply companies.
Another advantage of this technique is that if the system is empty, you can charge the system with the
Hydrogen/Nitrogen mix and vent the gas directly to that atmosphere when the leak is identified. This
saves considerable time since the traditional technique is to charge the system with some refrigerant and
use a conventional and less accurate leak detector to check for leaks. The test charge of refrigerant must
then be recoverd from the system.
Dye Leak Testing
Leak checking with a fluorescent dye and
ultra violet (UV) light is a reliable and
effective leak detection method. However it
does have some drawbacks. You must be
able to see the point of the leak either
directly or at least indirectly by using a
mirror or borescope. Confirming evaporator
leaks can be especially challenging using
dye. Depending on the size of the leak, the
system must be run for varying lengths of
time before the dye will show up. It can take
several days for very small leaks to become apparent. Dye is carried in the oil. If the leak is at a high
point in the system where little oil reaches, the leak may not show up at all. In addition, once an area is
Dye Leak Detection Kit
Trace Gas Leak Detection Using a 5% Hydrogen/95%
Nitrogen Gas Mix

Air conditioning diagnosis service and repair v2

Air conditioning diagnosis service and repair v2

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