The air brake dryer desiccant cartridge requires replacement.

Replace the desiccant cartridge.

The air system was charged from an external air source. Air is not passing through the air brake dryer.

Decrease use of the inflation valve in order to charge the system.

The air brake dryer is not purging.

Refer to Air Brake Dryer Does Not Purge or Exhaust Air .

The purge (air exhaust) time is too short because of excessive system leakage.

Refer to Air Brake Dryer Constantly Cycling or Purging .