With the Buick A/C compressor functioning properly, a stable and constant temperature in the cabin of your car can always be maintained. The function of the A/C compressor is to compress the refrigerant in the air conditioning system so the expansion of it can occur causing the cooling effect felt by the driver and passengers. In all Buick models the A/C compressor comes on when the temperature control device is switched to cooling. Unknown to most drivers is that the A/C compressor is also used when the switch is changed to the defrost mode. This is done because of the physical principle of cold air that has a lower moisture level and helps to clear fogged up windows due to high moisture content in the air. This feature is not unique to Buick models but for all cars made today. The Buick A/C compressor is like what is on most other vehicles on the road. It is one of the accessories on the front of the engine that receives it kinetic power from the serpentine belt. The portion of the compressor that is in front of the pulley is called the A/C clutch. When the clutch is engaged, the A/C compressor is actually turning. And refrigerant is being compressed in the system producing cold, low moisture air. The owners of Buick models will know their air conditioning system is activated when they hear a clicking sound from the clutch and the A/C clutch begins to spin. Even when the air conditioning is on, the compressor cycles on and off because the demand for cooling has already been reached. Because of this never touch the clutch while your vehicle is running. It might kick on and take a finger off at any time without warning.