Medium Duty Operator's Manual - Peterbilt Motors Company

Preventive Maintenance
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 continuously
while the engine is running. System pressure is controlled
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 pressure
falls to 100 psi (690 kPa).
Preventive Maintenance
The following service checks are provided for your information
only and should be performed by a certified mechanic.
Contact your Peterbilt Dealer or consult the Medium Duty
Air System
Maintenance Manual and the engine manufacturer's Maintenance
Manual for further information on servicing air compressors.
After completing any repairs to the air system,
always test for air leaks, and check the brakes for safe operation
before putting the vehicle in service.
According to Table 5, “Air System Scheduled Maintenance,”
Page 192:
• 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 carbon
is found, clean or replace the compressor cylinder
head. Also, check compressor discharge line for carbon,
and clean or replace the discharge line if necessary.
• Disassemble compressor and thoroughly clean and
inspect all parts. Repair or replace all worn or damaged
parts, or replace compressor with a factory exchange
unit.
Medium Duty (R05/09) Y53-6008A – 195 –