Excessive air brake dryer purge valve leakage is evident.

Inspect for excessive leakage with the air compressor loaded. Apply a soap solution on the purge valve exhaust. If the leakage is excessive, overhaul or replace the air brake dryer.

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 .

The purge control line is connected to one of the following components:

Connect the control line to the unloader port of the governor.

The heater and thermostat or wiring are faulty. A fuse is blown.

Test the electrical circuit.

The inlet and the outlet air connections are reversed.

Connect the lines properly.

The check valve between the air brake dryer and the supply reservoir is faulty.

1. Test the check valve for proper operation. 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 25 mm (1 in) bubble in five seconds. If leakage is excessive, replace the check valve.

The discharge line is kinked or blocked.

Clean or replace the line as needed.

Excessive bends in the discharge line cause the water to collect and freeze.

Correct the discharge line routing.

Excessive system leakage is evident.

Inspect for system leakage. Repair or replace parts as needed.