Remove the air governor or air governor signal line from the air compressor. Install the pipe plugs into all of the air
governor unloader ports on the air compressor.
Operate the engine to activate the air compressor.
If the air system pressure does not rise, the unloader valve assembly is malfunctioning. Clean the air compressor
cylinder head. Refer to Procedure 012-003 in Section 12.
If the air compressor has multiple air governor unloader ports, install a pipe plug into one of the ports, and a shop
air fitting into the other unloader port.
Connect a regulated shop air hose to the fitting in the unloader port.
Operate the engine to activate the air compressor.
When the air system pressure has reached 586 kPa [85 PSI], apply 698 kPa [1 00 psig] of shop air pressure to the
unloader port. If the vehicle air system pressure continues rising, the unloader valve assembly is malfunctioning.
Clean the air compressor cylinder head. Refer to Procedure 012-003 in Section 12.
Connect the OEM air governor signal line to the air compressor unloader port.
Operate the engine to activate the air compressor. Verify that the system still builds pressure properly.
If the air system pressure continues to build beyond the governed point, the air governor is malfunctioning. Refer
to Procedure 012-016 in Section 12.
