Q: Squealing from AC Clutch

The A/C compressor has an electrically controlled clutch mechanism, part of which is visible. The clutch is adjacent to the A/C compressor pulley that has the serpentine belt on it.

When the car is running, and A/C is off you should see the pulley only turning. As you view the pulley turning, have an assistant turn the A/C on max. Make sure car is in park with emergency brake on and wheels are blocked. Do not stand in front of the car, stand to the side.

When your assistant turns A/C on max (blower on, too) you should see the clutch turn with the pulley. That signifies that the compressor is at least "turning" as the clutch is now locked to the pulley.

Now, have the assistant turn max "off" (i.e., use regular A/C setting). The clutch should still be engaged and turning with the pulley, although the clutch might cycle on and off which is normal as the cooling load will vary. If the clutch does not engage with the "normal A/C" setting there is a problem, possibly electrical but also possibly related to the level of refrigerant charge.

You should check the refrigerant charge using a manifold to confirm that pressures are within normal range (if pressures are too low, there is a switch in the system that will shut down the compressor because low pressure does not adequately lubricate the compressor; it is a safety switch).

The squealing sound could have a variety of causes: A/C clutch slipping (in turn would have a variety of causes); belt is damaged, old and worn; misaligned belt pulleys including that on harmonic crankshaft balancer; damaged or dried out (grease) pulley bearings; A/C compressor shaft bearing is bad.

If you feel like this repair may be over your head, have one of our mobile technicians perform these checks and diagnose the issue with your A/C system for an accurate repair. Best of luck.