PERFORMANCE TESTS - CONTINUED - TM-9-2320-312-24-10803

TM 9-2320-312-24-1

AIR CONDITIONING SYSTEM GENERAL MAINTENANCE AND TESTING - CONTINUED

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PERFORMANCE TESTS - CONTINUED

Evaporator.

Evaporator coils are basically trouble-free when air flow over 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 system and cannot be traced to other parts or fittings, suspect damage to one of evaporator coils.

Notify your supervisor.

Condenser.

The condenser is usually trouble-free. Normally, temperature of condenser outlet line is noticeably cooler than

inlet line. However, when road debris (such as leaves or dirt buildup) builds up, air flow over condenser fins is

blocked and air is not able to absorb enough heat to turn hot refrigerant gas into a liquid. High head pressures will

result. In this case, carefully clean outer surfaces of the condenser with compressed air or soap and water solution

using care not to bend fins.

High head pressures also occur if the condenser tubing is abnormally bent, blocking flow of refrigerant. Frost will

appear at point where 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 if poor system performance is caused by condenser is to direct a spray of water onto con-

denser while system is running. If the air conditioner cools better because of the assist provided by water, the con-

denser is not working.

When troubleshooting a suspected condenser problem, remember that the problem may be caused by radiator

transferring high levels of heat to condenser.

Thermostatic Switch.

NOTE

Before troubleshooting thermostatic switch, notify your supervisor to check for a full charge of

refrigerant in system. Compressor will not operate or will cycle too often if there is not enough

refrigerant in the system.

Quick or delayed cycling of compressor may be caused by a thermostatic switch that is work-

ing, but is out of adjustment. If, after performing tests below, switch seems to be out of adjust-

ment, replace switch (the thermostatic switch cannot be recalibrated).

Ensure that compressor clutch is operating properly.

Expose evaporator coil.

Start engine. Place air conditioner control at coldest setting and turn on air conditioner and fan.

Place an accurate thermometer in contact with a tube on evaporator coil. Ensure that thermometer is in good con-

tact with tube or incorrect reading will result. When temperature drops below 31-36F (-1-2C), compressor clutch

should disengage and remain this way until temperature rises to 39-44F (4 -7C).

If the compressor did not engage when temperature was above accepted high range, perform the following test:

(1)

Connect voltmeter or test light from one terminal on thermostatic switch to ground. Repeat this test with

other terminal on switch.

(2)

With engine running and air conditioner and blower on, both terminals will show voltage when compres-

sor should be engaged. One terminal will show voltage when compressor should be disengaged. If voltage

is not present, there is a problem in electrical system from batteries to thermostatic switch. Check all cir-

cuits for cause, and repair or replace necessary wiring or parts. In all other cases where compressor is not

engaging and disengaging properly, thermostatic switch is cause. Replace thermostatic switch.

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