Abstract: An air supply system for a vehicle includes an internal combustion engine that powers the vehicle and a compressor that receives air from the intake manifold of the engine or from an air filter. The compressor operates in either a loading or unloading mode and supplies air to the vehicle braking system. During the loading mode, air flows from the compressor through a dryer and is stored in a reservoir that supplies air to the brakes when the brakes are actuated. The dryer removes moisture and contaminants from the compressed air before the air is stored in the reservoir. A valve independently controls the compressor and dryer. A first sensor produces a fueling status signal in response to monitoring the fueling status of the engine and a second sensor produces a reservoir pressure signal in response to measuring the air pressure in the reservoir.