The AC Compressor is the heart of the AC system on your truck. The compressor pumps the refrigerant to keep it circulating and to increase the refrigerant's pressure. The compressor is made up of 2 parts, the compressor itself and the clutch. The compressor will have 2 ports, and inlet and outlet, also called suction and discharge ports. There are a couple different types of compressors, the first being called a reciprocating compressor, which are the Blissfield and York style compressors. The second type is known as a rotary type, and these are the Sanden and Seltec models.