3
Troubleshooting
5
Meritor WABCO
Maintenance Manual MM-1012 (Issued 02-10)
3 Troubleshooting
Oil and Other Contaminants
The air control unit does not require maintenance. However, the ACU
can be affected by oil and other contaminants suspended in the air
as an aerosol. When these contaminants flow through the ACU, it
can cause the O-rings and rubber components to swell, affecting
the ability of the ACU to correctly control the air pressure.
Contaminants can also pass through the ACU and contaminate the
urea dosing system.
To prevent contaminants from reaching the ACU, an oil coalescing
device must be installed between the air compressor and the air
control unit. Either an air dryer with an integrated coalescing
desiccant cartridge or a standalone oil coalescing device is required.
Follow correct maintenance procedures and intervals for the oil
coalescing device used. If you do not use an oil coalescing device,
you will void any and all warranties provided on the ACU.
ACU Replacement
If there is a problem with the ACU functioning correctly, replace the
entire valve. Do not attempt to service or repair the valve. Refer to
Limited Warranty Document TP-1011 for warranty information.
Diagnostics
Condition
Possible Cause
Solution
ACU does not deliver air.
There is no voltage to the ACU.
Check the vehicle fuse/power supply.
The ACU solenoid is not operating.
Replace the ACU.
The check valve is stuck in the closed
position.
Replace the ACU.
Air pressure delivered to the SCR dosing unit
is too high or too low.
The pressure limiting portion of the ACU is not
functioning.
Replace the ACU.
