PERFORMANCE TESTS - CONTINUED - TM-9-2320-303-24-10130

TM 9-2320-303-24-1

AIR CONDITIONING SYSTEM TROUBLESHOOTING AND TESTING - CONTINUED

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PERFORMANCE TESTS - CONTINUED

Cooling System:

Although they are not physically connected, there is a close tie between a vehicle's air conditioner and its cooling

system. Poor air conditioner cooling can be the result of a problem in the cooling system.

If the cooling system does not work correctly, the heat of the engine will rise to abnormal levels. The added heat

will transfer to the air conditioner, other underhood parts, and maybe make its way into the cab. The added heat

makes it necessary for the air conditioner to work harder and, at the same time, it reduces the air conditioner's abil-

ity to cool down the air in the cab. Also, if the water regulating valve isn't closing all the way, heat will enter the

cab, giving the impression that the air conditioning system is not working.

Expansion Valve:

(1)

(a) 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 build-up.

(b) 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.

from the system. These contaminants should cause the moisture indicator's element to turn white and

then pink.

Refrigerant Compressor:

(2)

(a) Compressor problems usually show in one of four ways: abnormal noise; seizure; leakage; or low suc-

tion and discharge pressures.

(b) Resonant compressor noises are not causes for alarm; irregular noise or rattles are likely to be caused

by broken parts.

Evaporator:

(3)

(a) 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.

(b) If a leak exists in the system, and it cannot be traced to other parts or fittings, suspect damage to one of

the evaporator coils. Notify your supervisor.

Condenser:

(4)

(a) The condenser is usually trouble-free. Normally, the temperature of the condenser outlet line is notice-

ably 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 refrig-

erant gas into a liquid. High head pressures will result. In these cases, carefully clean off the outer sur-

faces of the condenser with compressed air or a soap and water solution; be careful not to bend the

fins.

(b) 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.

of refrigerant.

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