TM 10-5410-228-24
3.5
GENERAL AIR CONDITIONING MALFUNCTIONS Continued.
1. NO AIR CONDITIONING OR INSUFFICIENT COOLING.
NOTE
The following malfunctioning pressure symptoms are likely.
High (Compressed) Head Pressure. This is normally caused by high (warm) air temperature of the air to the
condenser coil, insufficient air across condenser, too great a R22 refrigerant charge, a dirty condenser, or air
in the R22 refrigeration system. Note: Too high a (compressor) head pressure will cause the air conditioning
system to shut down and the HIGH R22 REFRIGERANT PRESSURE alarm light on the rear control pane
to turn on.
Operating the air conditioning system with abnormally low superheat (gas temperature
above the saturation pressure point) can cause high suction pressure since some of the liquid
R22 refrigerant will evaporate in the suction line and possibly in the compressor itself. This
condition may damage the compressor.
Low (Compressor) Head Pressure. Low head pressure is normally caused when operating the air conditioner
with a low (cold) outside air temperature.
High Suction Line Pressure. This condition can be caused by a bad thermal expansion valve, a problem with
the sensor bulb, a bad compressor, or when the air in the ABS is warm and is accompanied by high warm
temperature of air being applied to the condenser (high head pressure).
Low Suction Line Pressure. This is normally caused by insufficient air flow or low (warm) temperature air
flow to the evaporator coil. It can also be caused by restricted R22 refrigerant flow or short R22 refrigerant
charge, problem with thermal expansion valve, or low head pressure. Too low a suction line pressure will
cause the air conditioning system to shut down and the LOW R22 REFRIGERANT PRESSURE alarm light
on the rear control panel to turn on.
Always wear eye protection and use extreme care when working with R22 refrigerant.
The R22 refrigerant system is pressurized. To prevent injury to personnel, gloves and eye
protection must be worn when working on R22 refrigerant system.
Prevent contact of R22 refrigerant with flame or hot surface. Heat causes R22 refrigerant to
break down and form carbonyl chloride (phosgene), a highly toxic and corrosive gas.
R22 refrigerant must be recovered. Venting R22 refrigerant into the atmosphere is a
violation of public law and subject to severe penalties.
Do not attempt to remove or connect refrigerant servicing equipment while ECV is running.
Failure to observe these warnings can result in injury to personnel.
NOTE
When checking the operation of the air conditioning system or troubleshooting the system, a
manifold gage set should e used (Item 26, Appendix B).
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