PERFORMANCE TESTS - CONTINUED - TM-9-2320-303-24-20034

TM 9-2320-303-24-2

AIR CONDITIONING SYSTEM TROUBLESHOOTING AND TESTING - CONTINUED

0227 00

PERFORMANCE TESTS - CONTINUED

Refer to WP 0009 00 to troubleshoot engine cooling system.

Expansion Valve.

Problems that start in the expansion valve show up as follows: when stuck closed, the evaporator coil and the

expansion valve will be at outside temperature; when stuck open, both the coil and the valve will be extremely cold

with frost or ice buildup.

Because the expansion valve channels are very small, blockages in the system tend to be found here (the valve is

very sensitive to contamination). Usually, the contaminant is water; less than a drop of water is all it takes to make

the valve inoperative. When water reaches the valve, the extreme cold that results from the pressure drop freezes

the water, forming a block of ice in the valve. After the system shuts down and the valve warms up, the ice melts,

and the valve operates again, only to freeze up when the moisture returns.

On-and-off operation of the expansion valve means that the receiver-dryer is not removing moisture from the sys-

tem. These contaminants should cause the moisture indicator's element to turn white and then pink.

Refrigerant Compressor.

Compressor problems usually show in one of four ways: abnormal noise; seizure; leakage; or low suction and dis-

charge pressures.

Resonant compressor noises are not causes for alarm; irregular noise or rattles are likely to be caused by broken

parts.

Evaporator.

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-

rator coils.

Condenser.

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 condenser's 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 WP 0009 00 to troubleshoot the engine cooling system.

Thermostatic Switch.

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 (WP 0214 00) (the

thermostatic switch cannot be recalibrated).

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