I didn’t realize the air conditioner clutch had fallen off my car until the weather warmed up the following spring. After confirming that the refrigerant level was normal, I noticed the compressor looked unusual. That’s when I discovered the clutch was missing.

The air conditioner uses an electromagnetic clutch made up of three main components: the coil (electromagnet), the pulley with its bearing, and the clutch plate. When the coil is energized, it pulls the clutch plate against the face of the pulley, locking them together so they rotate as one. Since the clutch is splined to the compressor shaft, this engages the compressor and allows it to operate.

The construction of the clutch itself is quite interesting. It consists of two separate components: a hub and a friction plate. The hub is splined to the compressor shaft, while the friction plate is connected to the hub via three spring-loaded pins. These pins allow the friction plate to move slightly away from the hub when not engaged.

When the electromagnet is energized, it pulls the friction plate away from the hub and toward the pulley, causing the plate to engage with the pulley and transmit rotation to the hub—and thus to the compressor. The friction plate and its mating surface on the pulley are lightly grooved perpendicular to the direction of rotation, enhancing grip through increased friction. Once the electromagnet is de-energized, the spring-loaded pins return the friction plate to its original position, disengaging it from the pulley.