Unlike commercial or residential A/C compressors where the motor is integral to the design, every automotive A/C compressor design is belt driven. With the use of a compressor clutch, the A/C compressor can be engaged and disengaged as required. The clutch assembly on automotive A/C compressor is typically referred to as an electro magnetic clutch. That is because the clutch only engages when the clutch coil creates a magnetic field strong enough to pull the clutch plate into contact with the pulley.

Every electro magnetic clutch assembly includes three distinct components. The clutch field or clutch coil is mounted on the front head of the compressor. The coil is the component that is connected to battery voltage and will create the magnetic field.

The pulley is the component that the drive belt attaches to. The pulley will turn with the drive belt at all times that the engine is operating. When there compressor is not engaged or there is no magnetic field being created, the pulley is free wheeling.

The clutch hub or clutch plate is furthest to the front of the compressor. The front hub is attached to the main shaft of the compressor. Also attached to the front hub is a clutch plate. That plate is attached by leaf spring or rubber. When the coil creates the magnetic field, the clutch plate is pulled into contact with the pulley and turns at the same speed as the engine. Because the clutch hub is attached to the main shaft of the compressor, when the clutch plate is engaged, the compressor can pump and circulate refrigerant throughout the A/C system.