The air conditioner assembly is comprised of the compressors, condenser, evaporator, thermal expansion valve, and the drier or accumulator.

These cooling or heating systems should be replaced when some of them fail to work as required. A compressor should be replaced when it fails to functions as required. This can be signaled by the development of noise, the inability of the system to cool, and an error code in the air-conditioning control unit or engine's central control unit. It also should be checked by a professional mechanic when some problems are diagnosed from it and replaced the faulty parts.