AXLE GP 4209919 - Caterpillar

Symptom
The air compressor constantly cycles. The air compressor remains unloaded for a very short time.Probable Cause
Excessive system leakageTest for excessive system leakage. Park the vehicle on a level surface.Engage the vehicle parking brake. Leave the engine running.Disconnect any trailers from the vehicle.Chock the wheels of the vehicle in order to prevent the vehicle from moving. Release the parking brake.Build up the air reservoir to the pressure for the governor cutout.Shut off the engine. Allow the air pressure gauges to stabilize for 1 minute. Then time the pressure drop on the gauges by the minute.Do not apply the brakes. The air leakage should not be more than 2 psi per minute.Apply the brakes. The air leakage should not be more than 3 psi per minute.Use soapy water to detect air leaks. High frequency meters may be used to detect air leaks. If pressure drop is excessive make the necessary repairs.
Leaking compressor unloader pistonRemove the inlet fitting of the air compressor. Disconnect the unloader line. Pressurize the unloader port of the air compressor with shop air. No leakage should be detected. Remove the governor from the back of the air compressor cylinder head and/or remove the line to the air compressor. Install a hose in the signal port to the unloader piston with a gauge and a shut off valve. Use shop air and charge the unloader port in order to unload the air compressor. Shut off the air supply and observe the gauge. A steady reading on the gauge indicates that there is no leakage. There should not be the sound of an air leak. If the unloader piston is leaking or if the unloader piston is stuck, then remove the unloader piston and then replace the unloader piston. Use a flashlight to look through the port for the unloader piston in the air compressor. Check for a carbon buildup inside the port for the unloader piston and/or check for damage to the intake reed. If there is no carbon buildup or if there is no internal damage install a new 217-5237 Unloader Kit .
Faulty governorVerify that the governor is of the proper type and the proper pressure rating for the air compressor. Test the governor for the proper operation. Test the governor by charging the supply tank with shop air to the specified operating pressure of the system. No air should be exhausting from the exhaust port of the governor. Repair the governor or replace the governor , if necessary.
Leakage from the air dryer Air should only be exhausting from the purge valve of the air dryer during the purge cycle. Inspect all fittings and all air lines for leakage. Check the air dryer purge valve for leakage. Test the air dryer purge valve by charging the supply tank with shop air to the specified operating pressure of the system. No air should be leaking from the purge valve. The check valve may be malfunctioning if leakage occurs after the purge cycle.Repair the system components or replace the