B5.9G, B5.9LPG – Troubleshooting and Repair Manual – Air Compressor Will Not Maintain Adequate Air Pressure (Not Pumping Continuously)

Air system leaks

Block the vehicle wheels and check the air system for leaks with spring brakes applied and released. Check for leaks from the air compressor gaskets and the air system hoses, fittings, tanks, and valves. Refer to the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.

Air compressor cylinder head is cracked or porous, or has a leaking gasket

Inspect the air compressor cylinder head and gasket. Refer to Procedures 012-103 and 012-104 and the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.

Air governor is malfunctioning or not set correctly

Check the air governor for correct operation. Refer to the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.

Air compressor intake or exhaust valve leaks air

Inspect the air compressor intake and exhaust valve assemblies. Refer to the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.

Air compressor is excessively worn or internally damaged

Replace or rebuild the air compressor. Refer to the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.

Air compressor not designed for application

Check the air compressor duty cycle. Install a larger air compressor, if necessary. Refer to the Master Repair Manual, Holset® Air Compressors, Bulletin 3666121, and the OEM service manual.