Service Manual

ISB, ISBe and QSB (Common Rail [...] Air Governor (Air Compressor Pumps Continuously)
Section 12 - Compressed Air System - Group 12 Page 12-31
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Activate the air compressor and allow the air pressure to
buildup.
If pressure is reading below 125 psi according to the dash
gauge, relieve 25 psi of pressure by applying the vehicle
brakes to see if the air compressor starts to pump again.
If the air compressor only pumps to the level it was before
then the air governor needs to be inspected for proper
operation. Refer to the original equipment manufacturer
(OEM) service manual.
Air Governor (Air Compressor Pumps
Continuously) (012-018)
Initial Check
Verify the unused unloader port, if applicable, on the air
compressor has a pipe plug installed.
Remove and inspect the air governor signal line from the
air compressor for kinks, cuts, nicks or plugging inside the
line.
Install pipe plugs in the air governor unloader ports.
Operate the engine to activate the air compressor.
If air pressure stops rising, there is a leak in an accessory
or an accessory air line. Refer to the original equipment
manufacturer (OEM) service manual for troubleshooting
and repair.
If the air compressor does not stop pumping (air pressure
continues to rise) at the governed air pressure, connect a
regulated shop air pressure line to the air compressor
unloader valve port.