Compressing and circulating refrigerant to chill and dry the air are the functions of AC (air conditioning) compressors, which are part of air conditioning systems. Refrigerant gas is compressed by an AC compressor before being pushed through a condenser to liberate heat. An evaporator is used to expand and chill the refrigerant after which heat from the interior of the house or vehicle is absorbed. The cycle is then repeated by returning the cooled refrigerant to the compressor. The efficiency and effectiveness of the air conditioning system are directly influenced by the AC compressor, a vital part of the refrigeration cycle.