Earlier this month, we talked about cooling system maintenance, but sometimes an a/c compressor failure happens. Second only to refrigerant hose leaks, compressors have the highest rate of failure of any motor vehicle air conditioner (HVAC) component. Yet compressors very seldom fail on their own and it is imperative that the cause of failure be properly diagnosed and corrected when replacing the compressor. If this is not done, your replacement compressor will also fail in a very short time.
A compressor is an engine. Engine failure is almost always caused by a lubrication or a “coolant” problem. Compressors fail for the same reasons.
Referring to the air conditioner, “coolant failure” means not dissipating heat from the condenser or having too much heat in the condenser. (Similar to a problem in the engine’s radiator). Too much heat means too high head pressure. On very hot days, this means a high side reading well over 300PSI. High head pressure is caused by:
- Too much refrigerant (Overcharge)
- A dirty bug screen or debris blocking the condenser
- A clogged radiator/cooling system
- A defective fan clutch or switch that activates the fan clutch
- A pinched tube in the condenser or too small of a condenser (if retrofitted or replaced)
- Improperly operating shutters
- Contaminated refrigerant
- Excessive air content (non-condensables gas) in system
Just as this is a common cause of engine problems, so too is lubrication failure that most common cause of compressor problems. Remember, the compressor needs to be lubricated by a special refrigerant compatible oil. The oil is “carried” through the a/c system by the refrigerant. The oil will not circulate without refrigerant. Therefore, compressor failure due to a lubrication problem is caused by:
Loss of refrigerant – which means no carrier of the oil and no lubrication for the compressor
A blockage in the system – keeps oil from returning to the compressor and will normally show up as too low a reading on the low pressure gauge.
“Too Low” a reading means 0-10 PSI or a vacuum. The blockage may be in the form of:
- A clogged filter drier/expansion valve/orifice tube.
- Moisture in the system. (If the air conditioner works okay for a short time then starts blowing hot air, the odds are that there is moisture in the system.)
- A defective thermostat or clutch cycling switch will cause the same symptoms, however a watery smell will also be present.
- A mechanically closed expansion valve. Some types may be removed and blown through (with mouth) to check.
Although these parts can be checked and cleaned, the service industry, as a general rule, will replace them.