Check Air Compressor Governor Cut-in and Cut-out Pressures. Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications) Run the engine at a fast idle. The air governor should cutout the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauges) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise. If the air governor does notwork as described above, it may need to be fixed. A governor that does notwork properly may not keep enough air pressure for safe driving.