Troubleshooting and Testing The Air

TM 9-2320-363-34-1 · Chapter 2 — Direct and General Support Maintenance Instructions

CONDITIONING SYSTEM (All Except M915A2 and M916A1)

Preliminarv Checks cool spots exist, replace the receiver-drier.

A blockage at the inlet of the unit will cause high Before testing the operation of the air conditioning head pressures; outlet blockages will cause low system, make the following checks: head pressures and little or no cooling.

1. Make sure the refrigerant compressor’s If the moisture indicator is pink or white (showing drive belt is not damaged and is correctly that the system is wet), the receiver-drier is tensioned. Also check the compressor saturated with moisture and must be replaced. mountings for tightness. COOLING SYSTEM

2. Check for broken, burst, or cut hoses; also check for loose fittings on all parts. Although they are not physically connected, there is a close tie between a vehicle’s air conditioner

3. Check for road debris build-up on the and its cooling system. Poor air conditioner condenser coil fins. Using air pressure and cooling can be the result of a problem in the a whiskbroom or a soapy spray of water, cooling system. carefully clean off the condenser; be careful not to bend the fins. If the cooling system does not work correctly, the heat of the engine will rise to abnormal levels. The

4. Check the color of the moisture indicator added heat will transfer to the air conditioner, sight glass. If the color is a deep cobalt blue, other underhood parts, and maybe make its way the refrigerant charge is dry. If the indicator into the cab. The added heat makes it necessary is not blue, the system is contaminated with for the air conditioner to work harder and at the moisture; recover the refrigerant, evacuate same time, it reduces the air conditioner’s ability the system, replace the receiver-drier, and to cool down the air in the cab. Also, if the water add a full refrigerant charge. regulating valve isn’t closing all the way, heat will enter the cab, giving the impression that the air

5. If there is not enough airflow, make sure that conditioning system is not working. leaves or other debris has not entered the fresh air ports under the windshield. If debris Refer to the engine cooling section for cooling has entered, it could clog the fins of the system troubleshooting. evaporator core, and block airflow. EXPANSION VALVE Also, be sure that all ducts are connected to the dash louvers and that the air-control Problems that start in the expansion valve show flaps in the heater housing are moving up as follows: when stuck closed, the evaporator properly (this requires removal of the right coil and the expansion valve will be at outside and center dash panel). temperature; when stuck open, both the coil and the valve will be extremely cold with frost or ice build-up. Performance Tests Because the expansion valve channels are very Following is a brief description of symptoms or small, blockages in the system tend to be found conditions that could exist if something goes here (the valve is very sensitive to contamination). wrong with a refrigerant part. Usually, the contaminant is water; less than a drop of water is all it takes to make the valve RECEIVER-DRIER inoperative. When water reaches the valve, the extreme cold that results from the pressure drop The receiver-drier is normally at outside freezes the water, forming a block of ice in the temperature. To the touch, the entire length of the valve. After the system shuts down and the valve warms up, the ice melts, and the valve operates unit should be the same temperature. If noticeable again, only to freeze up when moisture returns.

On-and-off operation of the expansion valve A quick test to check that poor system means that the receiver-drier is not removing performance is caused by the condenser is to moisture from the system. These contaminants direct a spray of water onto the condenser while should cause the moisture indicator’s element to the system is running. If the air conditioner cools turn white and then pink. better because of the assist provided by the water, it is a sign that the condenser is not REFRIGERANT COMPRESSOR working.

Compressor problems usually show in one of four When troubleshooting a suspected condenser ways: abnormal noise; seizure; leakage; or low problem, remember that the problem may be suction and discharge pressures. caused by the radiator transferring high levels of heat to the condenser. Refer to the radiator Resonant compressor noises are not causes for section for cooling system troubleshooting. alarm; irregular noise or rattles are likely to be caused by broken parts. To check for seizure, de- THERMOSTATIC SWITCH energize the magnetic clutch and see if the drive plate can be turned. If it won’t turn, the IMPORTANT: Before troubleshooting the thermo- compressor has seized. static switch, be sure there is a full charge of refrigerant in the system. The compressor will not Low discharge pressure may be caused by not operate, or will cycle too often, if there is not enough refrigerant, not enough belt tension, or a enough refrigerant in the system. blockage somewhere in the system. These things should be checked before servicing the Quick or delayed cycling of the compressor may compressor. be caused by a thermostatic switch that is working, but is out of adjustment. If, after doing EVAPORATOR the tests below, the switch seems to be out of adjustment, replace it (the thermostatic switch The evaporator coils are basically trouble-free cannot be recalibrated). when airflow over the fins is not blocked. External or, less often, internal blockages will cause low 1. Be sure the compressor clutch is operating suction pressure as well as little or no cooling. correctly.

If a leak exists in the system, and it cannot be 2. Expose the evaporator coil. traced to other parts or fittings, suspect damage to one of the evaporator coils. 3. Start the engine. Place the air conditioner control at its coldest setting; turn on the air CONDENSER conditioner and the fan.

The condenser is usually trouble-free. Normally, 4. Place an accurate thermometer in contact with the temperature of the condenser outlet line is a tube on the evaporator coil. Be sure the noticeably cooler that the inlet line. However, thermometer is in good contact with the tube, when road debris (such as leaves or dirt buildup) or you will get a wrong reading. cakes up, airflow over the condenser fins is blocked; air is not able to absorb enough heat to When the temperature drops below 31° to turn the hot refrigerant gas into a liquid. High head 36°F (-1° to 2°C), the compressor clutch pressures will result. In these cases, carefully should disengage and remain this way until clean off the outer surfaces of the condenser with the temperature rises to 39° to 44°F (4” to compressed air or a soap and water solution; be 7°C). careful not to bend the fins.

5. If the compressor did not engage when the High head pressures will also occur if the temperature was above the accepted high condenser’s tubing is abnormally bent, blocking range, do the following test: the flow of refrigerant. Frost will appear at the point where the flow is restricted. 5.1 Connect a voltmeter or a test light from one of the terminals on the Less common internal blockages (bits of foreign thermostatic switch to ground. Repeat material or metallic grit build-up) will stop the flow this test with the other terminal on the of refrigerant. switch.

TM 9-2320-363-34- 1

5.2 With the engine running and the air 7. Assemble the dash. conditioner and blower on, both terminals will show voltage when the LINE RESTRICTIONS compressor should be engaged; one terminal will show voltage when the A restricted suction line causes low suction compressor should be disengaged. pressure at the compressor and little or no cooling. A restriction in a line between the If there is no voltage, there is a compressor and the expansion valve can cause problem in the electrical system from high discharge and low suction pressure, and the batteries to the thermostatic insufficient cooling. switch. Check all circuits for the cause, and repair or replace the wiring Usually, areas of ice or frost build-up mean a or parts. blockage. Parts that often freeze up are probably corroded or inoperative and should be replaced. In all other cases where the Parts (such as the expansion valve) that freeze up compressor is not engaging and once in a while may do so because of moisture in disengaging properly, the thermostatic the system, which will cause the moisture switch is the cause. Replace it with a indicator’s element to turn white or pink; if this new switch. happens, recover the refrigerant charge, evacuate/recycle the system refrigerant, replace

6. Shut down the engine and, to prevent the receiver-drier,and install a new charge. accidental electric shock or shorting during dash assembling, disconnect the batteries.

Safety Precautions discharged, flushed, charged, and leak tested using an open flame leak detector.

Whenever repairs are made to any air conditioner Changes in both federal and state laws will affect parts that hold refrigerant, you must discharge, the way dealerships service air conditioning purge or flush (if contaminated), evacuate, charge systems. Under current federal laws, refrigerant and leak test the system. In a good system, must be recovered and recycled by all users to refrigerant lines are always under pressure and protect the environment, and not released into the you should disconnect them only after the air atmosphere. Many service operations not directly conditioning system has been discharged to a involving the air-conditioning system require the refrigerant recovery unit through the service release of the refrigerant charge. Under the new valves on the compressor. regulations, dealerships not having the required recovery and recycling equipment (and properly Refrigerants are safe when used under the right trained and certified personnel) will not be allowed conditions. Always wear safety goggles and non- to do any of this service work. leather gloves while discharging, purging, flushing, evacuating, charging, and leak testing the system. Because of its very low boiling point, refrigerant Do not wear leather gloves; when refrigerant gas must be stored under pressure. To prevent the or liquid contacts leather, the leather will stick to refrigerant cans from exploding, never expose your skin. them to temperatures higher than 125°F (52°C). Never leave refrigerant cans in the sun, and do WARNING: Use care to prevent refrigerant not store them in sun-exposed areas where heat from touching your skin or eyes, because liquid can build up, such as in gloveboxes, automobile refrigerant, when exposed to the air, quickly trunks, etc. evaporates and will freeze skin or eye tissue. Serious injury or blindness could result if you come in contact with liquid refrigerant.

Refrigerant splashed in the eyes should first be treated with a few drops of sterile mineral oil in the eyes, then rinsed with a weak boric acid solution. Do not rub the eyes. Call a doctor right away.

Refrigerant splashed on the skin should be treated the same as for frostbite: gently pour cool water on the area, but do not rub the skin. Keep the skin warm with layers of soft, sterile cloth. Call a doctor right away.

Even though refrigerant does not burn, when it contacts extreme heat or flame, poisonous phosgene gas is created. This gas is also produced when an open flame leak detector is used. Phosgene fumes have an acrid (bitter) smell.

WARNING: Do not work in an area where refrigerant may contact an open flame or any burning material, such as a cigarette. When it contacts extreme heat, refrigerant breaks down into poisonous phosgene gas which, if breathed, causes severe respiratory irritation. Do not breathe the fumes from an open flame leak detector.

You must work in an area where there is a constant flow of fresh air when the system is

A.   to resistor block                                     D. to engine fan thermal switch
B.   to blower motor                                       E. from a/c clutch relay
C.   from engine fan thermal switch                        F. to compressor clutch

1.   Compressor                       9. lgnition Switch                       17. Circuit Breaker (15A)
2.   Condenser                        10. Start Button                         18. A/C Clutch Relay
3    Receiver-Drier                   11. Circuit Breaker (10A)                19. Diode
4    Binary Switch                    12. Circuit Breaker (30A)                20. Compressor Clutch
5.   Moisture Indicator               13. Power Relay                          21. High-Speed Relay
6.   High Pressure Relief Valve       14. Blower Switch                        22. Fan Cycling Switch
7.   Expansion Valve                  15. “On-Off” Microswitch                 23. Discharge Service Valve
8.   Evaporator                       16. Thermostatic Switch                  24. Suction Service Valve

Problem - Little Or No Airflow

Possible Cause Remedy

The blower is not operating Check for an open circuit breaker. An open circuit indicates a short in the electrical system, which must be located and repaired.

Check the air conditioner relays for operation. Replace as necessary.

Make sure the blower motor switch is working. Replace if necessary.

Check the wiring to the blower motor. if any connections are loose, securely tighten them.

Check the blower motor for operation. Replace if sticking or otherwise inoperative.

Check the resistor block. Replace if necessary.

CAUTION: Never try to bypass the fuse in the resistor block. To do so could cause the blower motor to overheat, resulting in serious damage to the heater/air-conditioning system.

There are restrictions or leaks in the Examine ail air ducts and remove any blockages. Stop any leaks or air ducts. replace any portion where the leaks cannot be stopped.

ice has formed on the evaporator Defrost the evaporator coil before resuming operation of the air coil. conditioner.

PROBLEM - WARM AIRFLOW WHEN AIR CONDITIONER IS ON

Possible Cause Remedy

There is no refrigerant charge in the Repair any leaks, evacuate the system, replace receiver-drier, and add a system. full charge of refrigerant.

Moisture in the system. If moisture is in the system, ice crystals may form at the expansion valve, blocking the flow of refrigerant (off and on). Recover the refrigerant charge, replace the receiver-drier, evacuate the system, and add a full charge of refrigerant.

The refrigerant compressor is not If the refrigerant charge is low, charge the system. Repair any leaks. operating. The refrigerant compressor clutch needs repair or replacement.

PROBLEM - LOW EVAPORATOR COIL OUTLET PRESSURE (LOW COMPRESSOR SUCTION PRESSURE)

Possible Cause Remedy

The expansion valve is not working. Replace the expansion valve.

There are restrictions in the line to Remove the line restrictions. the expansion valve.

There is an insufficient refrigerant Locate the leak. Recover the charge, replace the receiver-drier, and add charge in the system. a full refrigerant charge.

Problem - High Compressor Discharge Pressure

Possible Cause Remedy

There is an internal restriction in the Replace the condenser. condenser. (Ice buildup on the condenser or a cool spot on the line from the condenser to the receiver- drier).

Air is present in the system. Repair any leaks, evacuate the system, and add a full charge of refrigerant.

Restriction in the compressor Repair or replace the line. discharge line.

PROBLEM - EVAPORATOR OUTLET AIR TEMPERATURE INCREASES AS COMPRESSOR DISCHARGE PRESSURE DROPS

Possible Cause Remedy

The expansion valve setting is too Replace the expansion valve. Add a full charge of refrigerant. low.

PROBLEM - COMPRESSOR OPERATES TOO OFTEN OR CONTINUOUSLY

Possible Cause Remedy

There is too little refrigerant in the Repair any leaks, and add a full charge of refrigerant. system.

There is a restriction in the Remove the restriction from the line. refrigerant system.

Possible Cause Remedy

The thermostatic switch operates, Replace the thermostatic switch. Do not attempt to adjust it. but is out of adjustment.

Loss of refrigerant is causing a Add a full charge of refrigerant. delayed cycling of the compressor.

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