AIR CONDITIONING SYSTEM TROUBLESHOOTING AND TESTING - CONTINUED
PERFORMANCE TESTS - CONTINUED
Compressor problems usually show in one of four ways: abnormal noise; seizure; leakage; or low suction and dis-
Resonant compressor noises are not causes for alarm; irregular noise or rattles are likely to be caused by broken
The evaporator coils are basically trouble-free when airflow over the fins is not blocked. External or, less often,
internal blockages will cause low suction pressure as well as little or no cooling.
If a leak exists in the system, and it cannot be traced to other parts or fittings, suspect damage to one of the evapo-
The condenser is usually trouble-free. Normally, the temperature of the condenser outlet line is noticeably cooler
than the inlet line. However, when road debris (such as leaves or dirt buildup) cakes up, airflow over the condenser
fins is blocked; air is not able to absorb enough heat to turn the hot refrigerant gas into a liquid. High head pres-
sures will result. In these cases, carefully clean off the outer surfaces of the condenser with compressed air or a
soap and water solution; be careful not to bend the fins.
High head pressures will also occur if the condensers tubing is abnormally bent, blocking the flow of refrigerant.
Frost will appear at the point where the flow is restricted.
Less common internal blockages (bits of foreign material or metallic grit buildup) will stop the flow of refrigerant.
A quick test to check that poor system performance is caused by the condenser is to direct a spray of water onto the
condenser while the system is running. If the air conditioner cools better because of the assist provided by the
water, it is a sign that the condenser is not working.
When troubleshooting a suspected condenser problem, remember that the problem may be caused by the radiator
transferring high levels of heat to the condenser. Refer to TM 9-2320-302-20 to troubleshoot the engine cooling
IMPORTANT: Before troubleshooting the thermostatic switch, check for a full charge of refrigerant in the system.
The compressor will not operate, or will cycle too often, if there is not enough refrigerant in the system.
Quick or delayed cycling of the compressor may be caused by a thermostatic switch that is working, but is out of
adjustment. If, after doing the tests below, the switch seems to be out of adjustment, replace it (TM 9-2320-302-20)
(the thermostatic switch cannot be recalibrated).
Ensure the compressor clutch is operating correctly.
Expose the evaporator coil.
Start the engine. Place the air conditioner control at its coldest setting; turn on the air conditioner and the
Place an accurate thermometer in contact with a tube on the evaporator coil. Ensure the thermometer is in
good contact with the tube or you will get a wrong reading.
When the temperature drops below 31°F to 36°F (-1°C to 2°C), the compressor clutch should disengage
and remain this way until the temperature rises to 39°F to 44°F (4°C to 7°C).
If the compressor did not engage when the temperature was above the accepted high range, do the follow-