Service Manual

Air Compressor ISB, ISBe and QSB (Common Rail [...]
Page 12-22 Section 12 - Compressed Air System - Group 12
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Connect the original equipment manufacturer (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 012-018 in Section 12.
• Refer to Procedure 012-017 in Section 12.
Air Compressor (012-014)
Pressure Test
WARNING
The external pressure tank used must meet SAE J10 and FMVSS121 standards, and have a safety pressure
relief valve which opens between [150 to 175 psi]. Failure to use the proper pressure vessel and plumbing can
result in property damage and serious personal injury.
Air Compressor Diagnostic Test
1 Park vehicle on a level surface and in an area where it is safe to idle for an extended period of time. Chock the
vehicle wheels or an appropriate anti-roll device to stabilize the vehicle.
2 Drain the vehicle air system.
3 Remove the air discharge hose and air governor signal hose from the air compressor.
4 Plumb an air discharge hose from the air compressor into an external pressure tank. The external pressure tank
must be equipped with a 1034 kPa [150 psi] pressure gauge and 1034 kPa [150 psi] pressure relief valve. Make
sure that the fittings are installed with appropriate thread sealant and do not leak.
5 Start the engine and operate at idle speed.
6 Record the amount of time required to fill the tank.
7
Divide the volume of the tank used (must be in in
3
), by the time (sec). This is the pressure rate.
8 If the pressure rate is lower than the rate in the Pressure Rate Chart, the air compressor is malfunctioning and the
air compressor cylinder head needs to be repaired, b ased on the marking scribed in the head. Refer to Procedure
012-003 in Section 12.
Pressure Rate Chart
Air Compressor Size Minimum Time (sec) Maximum Time (sec)
Tank Volume (in
3
) Rate Minimum (in
3
/
sec)
250cc 50 55 1000 18.18
318cc 40 45 1000 22.22
500cc 25 30 1000 33.33
636cc 20 25 1000 40
NOTE: Once the external pressure tank pressure reaches 862 kPa [125 psi], shut the engine OFF. Depending on the
size of the external tank and the diameter/length of the discharge hose being used, the buildup time will vary as shown
in the Pressure Rate Chart.
Verify that the air compressor will build pressure and the pressure rate is higher than the rate in the Pressure Rate
Chart. If air pressure successfully builds to 862 kPa [125 psi] and meets the pressure rate from the chart, the air
compressor is functioning properly. Remove the external air discharge hose from the air compressor and install the
vehicle air discharge hose and air governor signal hose to the compressor. Reference to the symptom tree being
utilized, to inspect the rest of the air system components for leaks and verify proper operation.