Air System Preventive Maintenance
– 164 – Y53-6008
Medium Duty (R10/06)
Follow the procedure below to check the compressed air
system for leaks:
1. Periodically, or after maintenance or replacement of air
system components:
2. Build up air pressure in the system to the governor cut-
out point or until 120 psi (827 kPa) is reached.
3. Stop the engine and release the service brakes.
4. Without applying the brake pedal, observe the rate of air
pressure drop. This rate should not exceed 2.0 psi (14
kPa) per minute.
5. Start the engine and build up the air pressure again.
6. Stop the engine, and apply the brakes fully. Apply the
brake pedal and hold it down for five minutes. The pres-
sure drop should not exceed 3.0 psi (21 kPa) per minute.
7. If you detect excessive leakage (air pressure loss greater
than 3.0 psi after five minutes of brake application), a
leakage test should be made at the air line connections
and at all air brake control units. These tests should
determine where air is escaping.
Air Compressor
Operation
All compressors, regardless of make or model, run continu-
ously while the engine is running. System pressure is con-
trolled by the governor. The governor acts in conjunction with
the unloading mechanism in the compressor cylinder block to
start and stop compression of air. The compressor is
unloaded when the system pressure reaches 120 psi (827
kPa) and compression is re-established when system pres-
sure falls to 100 psi (690 kPa).
Preventive Maintenance
The following service checks are provided for your informa-
tion only and should be performed by a certified mechanic.
Contact your Peterbilt Dealer or consult the Medium Duty
Maintenance Manual and the engine manufacturer's Main-
tenance Manual for further information on servicing air com-
pressors. After completing any repairs to the air system,
always test for air leaks, and check the brakes for safe opera-
tion before putting the vehicle in service.
According to Table 6, “
Air System Scheduled Maintenance,”
Page 161:
• Inspect compressor air filter element, if so equipped, and
replace element if clogged. Check compressor mounting
and drive for alignment and belt tension. Adjust if necessary.
• Remove compressor discharge valve cap nuts and
check for presence of excessive carbon. If excessive car-
bon is found, clean or replace the compressor cylinder
