A car AC compressor clutch is used to connect and disconnect drive power to the car’s AC compressor shaft. Unlike a car’s transmission clutch, an AC compressor clutch is either transmitting full drive power to the AC compressor or not—it’s not supposed to provide partial power. A slipping AC compressor clutch is a sign of severe wear, shorted clutch coil or an incorrect air gap (explained later).

Some engines use a dedicated drive belt to drive the AC compressor, while others use a drive belt that drives multiple components. The AC compressor drive belt rotates the compressor pulley at all times when the engine is running. But the pulley will not rotate the AC compressor shaft unless the compressor clutch has engaged.