Auto A/C Terms - Glossary
Magnetic Clutch

Auto A/C compressors are belt driven. The pulley that the belt attaches to will turn constantly whenever the vehicle is running. The magnetic clutch is a coupling device that will allow the internal portion of the compressor to become engaged so that the compressor turns with the rotation of the engine.

Magnetic clutches, also called electro magnetic clutches are made of three separate parts; the coil, pulley (which turns by drive belt from the engine) and hub (which is connected to the main shaft of the compressor). In order to engage the clutch, electric current is used to create a magnetic field by passing the current through the coil.

The coil is mounted on the front head of the A/C compressor, directly behind the pulley. That magnetic field created by the coil causes the (spring loaded) hub to be pulled in to contact the pulley. The magnetic field is strong enough to keep the hub engaged and turning with the pulley.

The most common problem on magnetic clutches is maintaining the air gap between the front hub and pulley. The air gap is there so that when disengaged, the pulley is allowed to turn freely. When the magnetic field is created, the hub is pulled in, eliminating the air gap, and becomes engaged. However, if the air gap becomes too great, the effect of the magnetic field is weakened and the front clutch hub will either not engage or engage and slip. Continued slipping of the clutch will lead to premature failure. In order to correct the problem, the air gap should be corrected.