Excessive leakage

Check the compressor unloaders, governor, and air dryer check valve.

The purge control line exhibits one of following conditions:

Determine if the air flows through the purge control line when the air compressor is unloaded. Repair or replace as needed.

Governor malfunction

Inspect the control lines to and from the governor for restrictions. Use a calibrated external gage in the supply reservoir, service reservoir, or reservoir port of the governor to verify cut-in and cut-out pressures. If governor is malfunctioning, replace it.

The air brake dryer purge valve is faulty.

Replace the purge valve.