Why Does an AC Compressor Clutch Engage and Disengage?

An air conditioner clutch that repeatedly engages and disengages is usually an indicator that the vehicle’s system is low on refrigerant. AAMCO recommends having the system checked and charged, as operating an air conditioning system in this condition causes further damage.

Air conditioners operate as a closed system. The same refrigerant cycles through the system many times. Air conditioners have sensors that determine the pressure and temperature of the refrigerant, starting and stopping the compressor by engaging or disengaging the clutch. As the vehicle ages, the system sometimes develops a leak. The reduced pressure causes the switches to misread the pressure of the refrigerant. Leaks allow moisture to invade the system as the coolant leaks. The units include a dryer to catch moisture before it causes the compressor to fail. Operating a leaking air conditioner has the potential to overload the dryer, resulting in system failure.

Automobile air conditioners work much like those used in homes. The greatest exception is that a belt from the car’s engine powers the compressor. The compressor transforms the refrigerant from a gas to a liquid. As the liquid expands back into a gas and passes through the system’s evaporator’s coils, it cools the air and reduces the humidity in the cabin of the vehicle.