Abstract: An air drying system for pneumatic circuits to provide compressed air at working pressure having a dew point which is below the temperature of the circuits. In one embodiment, the system has an air intake for accepting ambient air having an initial water vapor content, a compressor for over-compressing or highly compressing the air to a pressure which is greater than that necessary for operation of the pneumatic circuit, a heat exchanger which cools the highly compressed air below the dew point thereof to cause some of the water vapor to precipitate, and a regulator to expand the air, resulting in substantially unsaturated compressed air at a relatively moderate working pressure. In the preferred embodiment, the system is on a motor vehicle and the compressed air is cooled by the large volume of combustion air to the engine.