GILLIG LOW FLOOR, Service Manual

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Air System
Troubleshooting
Use the following chart to troubleshoot the Cummins 18.7 air compressor. If you have any questions or
need additional information, please contact Cummins Inc. at (800) 343-7357 for assistance.
Condition Possible Cause Solution
Blocked or restricted oil
return Clean oil drain passages in the compressor
and on the engine surface. Verify proper
passage alignment.
Contaminated inlet air or
oil Replace damaged, defective or dirty engine
air filter.
Repair any leaking, damaged or defective
compressor air intake components.
Change engine lubricating oil.
NOTE: To avoid this condition, make sure
vehicle manufacturerís oil and filter
maintenance schedules are followed.
Restricted air inlet or
excessive vacuum present
at compressor inlet Verify engine or compressor air cleaner is
functioning properly. Replace if necessary.
Repair compressor air inlet kinks or
excessive bends.
Check vehicle specifications to ensure air
and coolant lines meet all requirements.
Excessive engine
crankcase pressure Verify engine crankcase venting is to
manufacturerís specification.
Compressor duty cycle
too high Check system for leaks. Make necessary
repairs.
Compressor passes
excessive oil (for
example, the presence of
oil at exhaust air brake
system valves, oil in air
dryer desiccant, etc.)
None of the above, but
condition persists Replace the compressor.
Compressor leaks oil
Physical damage or
internal problems with
compressor
Replace the compressor.
Compressor unloader
piston leaking With compressor unloaded check for air
leakage. If leaking, replace the cylinder
head. and troubleshooting procedures.
Governor air leak Refer to the manufacturerís manual for
governor maintenance
Dryer purge valve air
leakage Check for air dryer malfunction. Refer to air
dryer manufacturerís service instructions.
Air leak at governor-
compressor attachment. Inspect connection for physical damage.
Inspect and repair connection.
Air leak at alcohol
injector Clear line of any obstructions. Inspect and
repair connection.
Excessive reservoir
contamination Drain reservoirs.
Compressor continuously
cycles
None of the above, but
condition persists Replace the compressor.