Excessive system leakage is evident.

1. Inspect for system leakage.
2. Repair the system.

Excessive leakage is evident in one or more of the following components:

1. Test the system for leakage at the following components:

•	The fittings

•	The reservoir drain valve (automatic type), if equipped

•	The safety valve in the supply reservoir

2. Repair or replace as needed.

The internal check valve is faulty.

1. Remove the check valve from the assembly from the end cover.
2. Apply air pressure to the delivery side of the valve.
3. Apply a soap solution at the opposite end.
4. Inspect for leakage. Permissible leakage is a 25 mm (1 in) bubble in 5 seconds.
5. If the leakage is excessive, replace the check valve.

The governor is faulty.

1. Inspect the governor for proper cut-in and cut-out pressures.
2. Inspect the governor for excessive leakage in both positions. Refer to Air Compressor and Governor Valve Diagnosis in Air Compressor.

The purge valve in the air brake dryer is leaking.

1. Open the supply port.
2. Apply 827 kPa (120 psi) at the control port.
3. Apply a soap solution to the supply port and the exhaust port (in the purge valve seat area). Permissible leakage is a 25 mm (1 in) bubble in 5 seconds.
4. If the leakage is excessive, replace the purge valve.

The compressor unloader mechanism is leaking.

1. Remove the air inlet hose and the fitting from the air compressor inlet cavity.
2. Inspect for leakage in the unloader piston while the air compressor is unloaded. Slight leakage is permissible.