Download causes of premature compressor failure

CAUSES OF PREMATURE COMPRESSOR FAILURE
Compressors have gone through some dramatic internal design changes since the early days of automotive air
conditioning. Overall, they are built much smaller and lighter than the units that were used on the older systems
and no longer contain oil pumps. As a result, they have to depend on the flow of refrigerant in the system to carry
the oil necessary to lubricate them. They also operate under more harsh conditions. Designs of late model
engine compartments and higher engine temperatures contribute to higher compressor operating temperatures.
In addition, R-134a tends to operate at higher pressures on the high side than the old R-12 and the combination
puts compressors under more stress.
Other design changes such as high-efficiency condensers which cannot be effectively flushed, systems with very
small refrigerant capacities where the charge has to be completely accurate, and problems with refrigerant crosscontamination and air contamination present new challenges for the modern day A/C technician. For this reason
and others that will be discussed, it is imperative that proper procedures be followed when repair work is being
done. Too many shops are trying to take short cuts and doing it the “old way” and as a result, they are
experiencing a high rate of premature compressor failures.
To help prevent future cases of premature compressor failure, we have identified the major causes and steps to
take to prevent these from occurring.
1. Contamination
A. System contaminated with debris from previous compressor failure. This can cause internal
restrictions that can starve the compressor of lubricant, create excessive high side pressure and cause
compressor overheating.
Condenser contamination. Because of their location, (just downstream of the compressor) most of the
debris that results from a compressor failure flows into the condenser and a lot of this material will remain
there. Older 3/8 tube and fin condensers can be easily flushed to remove debris but successful flushing is
much more difficult with the multi-flow and parallel flow condensers that are in common use today. As a
result, it is often necessary to replace a condenser rather than attempt to flush it
Dirty oil left in a system from a previous compressor failure. A technician would never consider re-using
dirty motor oil that had been removed from an engine that had failed but frequently dirty contaminated oil
is left in an A/C system and used with a replacement compressor. The system must be cleaned and
sanitized, and the correct amount and type of oil must be used.
B. Moisture contamination. Excessive moisture in an A/C system can saturate the desiccant in a drier and
promote corrosion and cause degradation of the system lubricant. Recovery/recycling machine filters
need to be replaced on a regular basis to prevent excessive levels of moisture in recycled refrigerant. A
proper vacuum needs to be pulled on a system prior to recharging to remove air and possible residual
moisture from the system. Most importantly, compressor warranty requires the replacement of the
system drier or accumulator, anytime the system has been opened or exposed to the ambient air.
C. Chemical contamination. Flush solvents that aren’t approved for use in A/C systems, or are not properly
removed from the system after flushing, can dilute and contaminate the fresh lubricant charge and will
cause accelerated wear between moving parts in the compressor.
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1. Trace dyes. Trace dyes used for finding leaks can dilute system lubricant resulting in accelerated
compressor wear. A quarter ounce of dye should be adequate for most automotive and small truck
applications, including those with dual evaporator systems (dual air).
2. Ester based flush solvents. Ester based flush solvents, which are actually very low viscosity ester oil,
should not be used to flush because they do not evaporate. Ester flush remaining in a system will
dilute and contaminate the system lubricant resulting in accelerated compressor wear.
3. Unapproved flushing agents. Unapproved flushing agents such as brake clean, WD-40, carburetor
cleaner, paint thinner, mineral spirits; Simple Green, etc. should not be used to flush. These
chemicals contain substances which can leave residues and attack elastomers which are used in orings, hoses, shaft seals, and other A/C components.
4. Sealers. There are A/C system sealers on the market which are used to stop system leaks (usually
in evaporators) which contain latex type material. These sealers are introduced into the system and
mix with the lubricant and are carried by the refrigerant. When they reach a point in the system
where there is a leak, the material will penetrate the leak and when it comes in contact with moisture
in the ambient air, the moisture will cause it to cure which will sometimes successfully seal the leak.
If a system happens to have moisture in it when the sealer is introduced or moisture is introduced at
a later time (such as when it is opened up for service work), the sealer can cure throughout the
system and cause lubrication problems and restrictions which can result in a premature compressor
failure. Once introduced, these sealers are almost impossible to remove.
D. Contaminated Refrigerant.
Refrigerant that is cross contaminated with another refrigerant or
contaminated with air can cause excessive high side pressure and increase loads on the compressor,
especially when operating at low speed conditions under high ambient temperatures. Air contamination
can also cause compressors to be noisy. Recycled refrigerant should be checked for the presence of air
(also called non-condensable gases) regularly. Refrigerant purity should be checked with a refrigerant
identifier.
2. Lubrication Problems
A. Use of wrong type of lubricant. All OE manufacturers specify the use of PAG lubricant in R-134a
systems except in some hybrid vehicles where the compressors are powered by an electric motor. These
vehicles use specially formulated ester oil (not the regular ester oil that is commonly marketed for
conventional use with R-134a.) R-12 uses mineral oil. Do not use mineral oil in an R-134a system. PAG
should not be used with R-12 unless it is a special double end capped PAG and the lubricant
manufacturer specifically approves of its’ use with R12. ALL compressor manufacturers report an
alarming amount of compressors being returned as defective that failed because they were
serviced with the wrong type of lubricant!
B. Correct type of lubricant, but wrong viscosity. There are 3 common viscosities of PAG lubricant; 46,
100, and150. It is imperative to use the one specified by the manufacturer.
C. Insufficient lubrication or no lubrication. Some manufacturers ship their compressors with varying
amounts of lubricant, while other manufacturers ship theirs dry. The only sure way to determine how
much lubricant is in a compressor is to drain it and measure it. The correct type, viscosity and amount of
lubricant must be used. ALL compressor manufacturers report an alarming amount of compressors
being returned as defective that were installed and failed because they were run with insufficient
amounts of lubricant or in some cases they were run without any lubricant!
D. Leaks. As refrigerant leaks, lubricant leaks with it. If a leaking system is continually topped off without
the lost lubricant being replaced, the system will suffer from lack of lubrication. The lubricant that is lost
from a system needs to be replaced.
E. Too much lubricant. If a system contains too much lubricant, the compressor can be damaged. In a
system properly charged with refrigerant and lubricant, the lubricant enters the compressor in a mist-like
form suspended in the gaseous refrigerant. In a system that contains too much lubricant, it enters in
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larger quantities and can bend or break reed valves. If there is any doubt about how much lubricant is in
the system, the best thing to do is to remove it all and install the correct amount. Too much lubricant can
also cause high head pressures and high duct temperatures.
3. Refrigerant Overcharge
A. Unlike R-12 systems, R-134a systems are very sensitive to overcharge, and an overcharge results in
higher than normal high side pressures. The combination of an overcharged system and high ambient
temperatures can place a high load on a compressor and can cause the clutch to slip. With system
charges steadily getting smaller and some systems now having a capacity of less than 1 pound, a couple
of extra ounces can result in an overcharge. Accurate charging on R-134a systems is very critical.
Charging equipment must be properly calibrated.
4. Refrigerant Undercharge
A. If a system is undercharged, the compressor will operate at a higher than normal temperature and will not
receive adequate lubrication. This is because the refrigerant both cools the compressor and carries the
lubricant throughout the system. With system charges steadily getting smaller and some systems now
having a capacity of less than 1 pound, an ounce or two low can result in an undercharge that can cause
lubrication problems, and premature compressor failures.
CAUTION: Charging with 12 ounces cans is very inaccurate and can cause problems.
5. Excessive High Side Pressure
A. Excessive high side pressure causes temperatures to increase throughout the system. This puts more
strain on the moving parts of the compressor and causes the lubricant to thin out and accelerate wear.
Excessive high side pressure is not caused by a malfunctioning compressor.
B. In addition to the internal restrictions, contaminated refrigerant, refrigerant overcharge and oil overcharge
that were mentioned previously, increased high side pressure can be caused by any conditions that
reduce airflow through the condenser, such as missing air dams, debris lodged in condenser fins,
defective fan clutches and malfunctioning electric radiator cooling fans.
6. Compressor Clutch Failure
Clutch Slippage. Compressor clutch failure is usually the result of a clutch slipping which generates a
tremendous amount of heat. A slipping clutch can reach a temperature of over 800 degrees Fahrenheit in
less than 3 minutes and this heat can melt the grease in the clutch bearing, causing it to fail. The heat can
also be transferred down the compressor shaft where it can damage the front shaft seal. The slipping doesn’t
usually occur because of anything wrong with the clutch itself, but rather because of one or more other
problems which can exist in a system. The failed clutch is a symptom of a problem or sometimes a
combination of problems. If the torque capacity of the clutch is exceeded or if there is an electrical problem
which prevents the clutch from reaching its’ torque capacity, slippage will result. If the clutch or
compressor/clutch combination is just replaced without determining the root cause and repairing it, there will
be another clutch failure. The most common reasons for clutch failure are examined below.
A. Excessive high side pressure. Excessive high side pressure puts extra strain on the compressor clutch
and can cause it to slip. Even though most vehicles now have high pressure cut-out switches, a clutch
can experience slippage before the switch shuts the system down, particularly if there are any other
problems in the clutch electrical circuit.
B. Low voltage. Low voltage can cause clutch slippage leading to premature clutch failure. The voltage
supplied to the clutch with the a/c system running should be within at least 1 volt of the electrical or
charging system voltage (usually 13.5 to 14.4 volts). A clutch will engage with as little as 10 volts or even
less but the coil may not generate enough magnetic force to properly clamp the hub and drive face
together. As a result, the clutch may slip.
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Low voltage is caused by voltage losses which occur as a result of high resistance in the clutch electrical
circuit. The high resistance will usually occur at connections or in switches or relays. The voltage to the
clutch should be checked with the a/c system operating and after the vehicle has warmed up to normal
running temperature. If low voltage is detected, it will be necessary to do voltage drop tests across each
connection, relay and switch in the clutch circuit to determine where the loss is occurring and what needs
to be repaired and replaced.
C. Poor ground. A poor ground to the clutch has the same effect as low voltage. Instead of all the voltage
being used to energize the clutch, part of it is used to overcome the high resistance caused by the poor
ground. A voltage drop test from the clutch ground terminal to the negative battery post will indicate if
there is a ground problem. A voltage drop of 1 volt or greater is cause for concern and if encountered
additional voltage drop tests across each connection should be conducted to isolate the problem.
D. Clutch air gap. Clutch air gaps are set at the factory but rough handling during shipping can change
them. Clutch gaps should always be checked prior to compressor installation and adjusted if not within
specs.
E. Malfunctioning pressure switches. Malfunctioning pressure switches can cause rapid clutch cycling
which can lead to premature clutch failure. Pressure cycling switches will generally disengage the
compressor clutch at about 24 to 26 psig low side operating pressure and re-engage it at around 44 psig.
Check the specs to determine the exact on and off pressures for these switches.
F. Low refrigerant charge. Low charge due to system leaks or undercharging of the system are also
responsible for clutch failure. This is due to lack of lubricant being returned to the compressor thereby
increasing internal load or friction on the various compressor components and increasing “drag” on the
clutch driver or “hub”.
G. High coil resistance. High resistance in the clutch field coil will also cause clutch failure. Normal
resistance readings should be 3 to 6 ohms at ambient or operating temperatures. Below ohms usually
indicates a “short” circuit in the coil, whereas 6 ohms or greater would indicate “high” resistance. Either
condition will cause or prevent proper clutch engagement.
H. Oil or fluid on the clutch hub and drive face. Oil or fluid leaking from components on the engine or
even from spillage when adding fluids can get on the clutch hub and drive face and cause clutch slippage.
Care must be taken not to spill fluids and if there are components which are leaking fluids on the clutch,
these leaks must be repaired.
I.
Clutch Burnishing. Clutch burnishing is a procedure similar to breaking in a new set of disc brake pads.
Burnishing can bring a new or remanufactured clutch up to its’ operating torque capacity quickly and
diminish the possibility of slippage during initial operation. To burnish a clutch, run the engine at about
1500 to 2500 RPM. Using the controls on the dash, cycle the clutch ON and OFF at a rate of 10 to 15
times per minute for a total of 40 to 50 cycles. This should bring the clutch up to its’ operating torque
capacity.
Failure to Diagnose and Repair the Root Cause of a previous compressor failure is the leading cause of
replacement compressor premature failure. There is a reason for every premature compressor
failure and most can be traced to one or a combination of the reasons outlined above. If a
compressor is just replaced and the cause of the failure not identified and repaired, another
failure will be imminent.
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