Auto A/C Terms - Glossary
Clutch Pulley or Rotor

Every auto A/C compressor uses an electro magnetic clutch assembly to operate the compressor. That assembly includes a coil to create the magnetic field, a clutch plate attached to the main shaft of the compressor which will engage and disengage the compressor and a pulley or rotor... which is the part of the clutch assembly the belt attached to. The pulley or rotor will turn or free wheel with the engine speed when the compressor is not engaged.

What is most important to check when servicing auto A/C systems is the air gap on the clutch. That is the distance between the front clutch hub or clutch plate and the pulley or rotor. If that air gap is too great, the magnetic field may not be strong enough to engage the clutch.

Additionally, you should confirm that the coil has full battery voltage available to assure the best magnetic field and that the ground circuit is secure and operating properly.