A properly functioning Chevrolet A/C compressor on your car will make it possible for your passenger to be comfortable when traveling along with you. This is the mechanism that provides for the cooling of the air in the cabin of your car by pressurizing refrigerant so it can be used. An A/C compressor is mounted to the front and to the side of the engine on all Chevrolets. It is powered by the serpentine belt. In front of the A/C compressor is the clutch pulley which engages and disengages as the air conditioning system on your car cycles. This is the clicking noise a driver hears when the air conditioning is turning on and off. The standard Chevrolet A/C compressor last for a considerable amount of time as long as the system is fully charge and has sufficient oil in it. The oil for the A/C compressor is placed in the system along with the refrigerant. The level of this oil cannot be checked with a sight glass or dip stick since it is mixed with the Freon gas. The temperature control lever or panel on the inside of your Chevrolet is how this device is controlled. It is activated in either the cooling capacity for the cabin or the defrosting mode for the windshield when required. If while the A/C compressor is running and a knocking sound can be heard coming from it, either the system needs additional oil to be added to it or the compressor itself needs to be replaced. Because of environmental concerns with the refrigerant used in this closed loop system, only authorized personnel are permitted to work on it. This is for all Chevrolets and other makes of car equipped with air conditioning. It is done to minimize the amount of Freon that escapes into the atmosphere which damages the ozone layer.