Air cycle machine

An air cycle machine (ACM) is the refrigeration unit of the environmental control system used in pressurized turbine-powered aircraft. Normally an aircraft has two to three of these machines arranged in a system called a "pack". The cooling process uses air instead of freon in a gas cycle. No condensation or evaporation is involved, and the cooled air output from the process is used directly for cabin ventilation.
See more at Wikipedia.org...