AC COMPRESSOR RELATED FAILURES & CAUSES

Seized or Slugging Compressor

The ac clutch function is to engage and disengage the ac compressor from the vehicle accessory drive system. If there is a system problem that prevents proper rotation of the compressor input shaft while the clutch is energized, the AC clutch will slip. A slipping clutch can generate tremendous heat, up to 1,200 degrees F. In a matter of seconds, components can start to fail. There is a progression of effects generated from slipping, all leading to overall clutch and/or compressor failure. Symptoms and causes are listed below:

A.Excessive A/C System Pressure The following problems will all increase system pressure. Just as too high blood pressure causes the heart to overwork, and prematurely fail, excessive A/C system pressure can cause the compressor to overwork, begin to seize, and increase the torque requirements of the clutch. The clutch will begin to slip, which produces tremendous heat build-up. Resultant clutch and bearing failure follows.

B.Loss of Lubrication:
- Loss of refrigerant will also prevent oil from returning to the AC compressor causing binding or lockup.
- A blockage or restriction somewhere in the system will also inhibit or prevent oil return to the compressor, thereby causing slipping, binding, or lockup.

C.Incorrect Amount of Oil in System
Too much oil can cause compressor slugging and a slipping clutch. Excessive oil can accumulate in the a/c condenser, increasing system discharge pressures. Not enough oil will cause compressor binding and AC clutch slipping.

D.Inadequate Air Flow across the Condenser
If the condenser is restricted internally, or has inadequate air flow across it, the result is a higher discharge pressure. This can cause the AC clutch to slip. Check the inlet and outlet temperatures of the condenser. A difference of over 35 degrees can indicate a problem. An inoperative or faulty radiator or condenser fan could also be suspect, or shutters not opening properly.

E.System Overcharge
An overcharged a/c system will cause pressures to increase and cause slipping. When checking for an overcharged system, remember to also check for the presence of non-condensables (air). This condition will also increase system pressures.

F.A Blockage in the High Pressure Side of the A/C System
A blockage will cause the discharge pressure to increase and can cause AC clutch slipping. A blockage in the system can usually be pinpointed by an immediate temperature (pressure) drop just following the blockage. Remember that a rise in pressure means a rise in temperature, and vice versa.