The AC compressor in your vehicle is part of the air conditioning (AC) system. It is a pump that compresses refrigerant in gaseous form and sends it to the condenser, its next destination in the system. The compressor is driven by the serpentine belt running around the compressor’s pulley. Since the serpentine belt is always moving whenever your engine is running, an electromagnetic clutch is employed in order to turn the compressor on and off.
The AC compressor clutch is energized by an electric current when you press the AC switch. If the AC is running, it is because the clutch is engaged. When the AC is switched off - or when the system is on, but additional cooling is not needed - the clutch disengages.
All the while, the serpentine belt continues to turn the compressor pulley and the internal shaft connected to it. With the clutch disengaged, the pulley essentially free-wheels, lessening the drag on the belt and increasing engine efficiency.
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