Aircraft air conditioner is an environmental control device in the aircraft, which plays the same role of air conditioning as household air conditioners. So why can't you just put your home air conditioner on the plane? This is because aircraft flight is a dynamic process, and processes such as climbing, descending, and cruising face severe tests of vibration, air pressure, and drastic changes in temperature.

Almost all of the air circulating in the aircraft comes from the aircraft air conditioning system, which is a major part of the aircraft cabin environmental control system. The cabin environmental control system provides the following three functions: cabin pressurization, temperature regulation, and equipment cooling.

Typical air conditioning systems provide bleed air from two engines or the APU (a separate gas turbine engine that provides power and air when the engines are not running). The bleed air from the engine is drawn from the medium-pressure or high-pressure compressor. Because of the compressor, it is very hot. Before entering the air-conditioning system, it must be pre-cooled by a precooler, and then sent to the air-conditioning system.