A/C Compressor and Clutch


Only EPA-certified technicians can purchase R-12 refrigerant, since proper recovery and recycling techniques are required to prevent damaging the environment. Improper disposal of R-12 refrigerant can result in a fine.

If the system is noisy:

  • A belt is loose, broken or frayed.
  • The clutch, clutch coil or clutch bearing is defective.
  • The compressor mounts or braces are loose.
  • An electrical connection is loose (causing a "chattering" clutch).
  • Refrigerant or oil is overcharged, or moisture is in the system. All cases require purging the system by a certified technician.
  • The system is leaking oil and/or refrigerant.
  • The blower fan is rubbing against the case, or the blower motor is defective.

If the system cools intermittently:

  • The electrical system contains a worn or loose wiring, an improperly grounded components, or a defective switch or control module.
  • The air conditioning blower motor, speed control, or resistors need replaced.
  • The A/C clutch coil is defective.
  • The A/C clutch is slipping due to wear or low voltage.
  • Belts are loose or broken.
  • The thermostat needs adjustment or is defective.
  • The high-pressure control, low-pressure control, or suction regulator needs replaced.

If the system does not provide sufficient cooling:

  • The circuit breakers are tripped or a fuse is blown. Check for other electrical system problems, such as broken, disconnected or corroded wires.
  • The A/C blower motor needs replaced.
  • The A/C clutch is slipping.
  • The A/C clutch coil is defective.
  • The thermostat is defective or needs adjustment.
  • The condenser needs to be cleaned.
  • The receiver-dryer, accumulator, or expansion tube or valve is clogged, requiring replacement.
  • A screen in the compressor, accumulator, expansion valve, orifice tube, or receiver-dryer is clogged. In some cases, the screen can be cleaned. In other cases, multiple parts may need to be replaced.
  • The system is leaking, requiring replacement of the expansion valve, shaft seal, or hoses.
  • The system needs refrigerant.

Check the tension and condition of the air conditioning drive belt. If the belt is not a serpentine belt, it probably requires higher tension than the other V-belts. Air conditioning compressors use a good deal of power when they run. A V-belt that has been allowed to slip will be glazed and will no longer hold the pulley, even if properly tensioned.


There are several things that can go wrong with a compressor. They can leak from the front shaft, from seals on the case, or from O-rings on the back. Sometimes, the aluminum tubing that supplies the back of the compressor develops a leak.

(a) O-rings on the back of a compressor. (b) An aluminum tubing manifold. Courtesy of Everco Temp Control.

There are hundreds of configurations of these. Aftermarket companies produce them and have catalogs listing them by number. Some mufflers have a filter that must be replaced in the event of a compressor failure. When you replace one compressor with another, it is important that the correct one be used. Be sure you have the correct part number. On the GM radial six-cylinder compressor there are twelve different part numbers. The difference is in where the compressor is mounted. It is important that the correct mounting be used so the oil passage is in the right place.

On orifice tube systems, oil is pulled up from the bottom of the receiver dryer. If the refrigerant level gets too low or if the oil hole gets plugged, the compressor can fail. Rebuilders recommend replacing the accumulator with every compressor replacement. This is because they do not want to take a chance that the oil hole is plugged and the newly rebuilt compressor will fail due to lack of lubrication.


Check the operation of the clutch. You should hear the loud click of the clutch as it engages periodically. Electric cooling fans should begin to run at low speed when the clutch comes on. Check wiring and hoses for obvious problems.

When clutch engagement problems occur, check for voltage from the source. Then use a jumper wire to apply power and ground to the terminals on the clutch. This will bypass the protection devices and determine whether the problem is the clutch or the circuitry. Parts of the clutch and compressor are shown below.

Parts of the clutch and compressor.