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CAS440HU Air Compressor Manual Part # 99901339
Troubleshooting Guide
Compressor Troubleshooting Guide
Symptom
Probable Cause
Air compressor slows
down as air pressure
increases and the engine
RPM remains the same,
or increases slightly.
1
Relief valve bypassing oil. Adjust relief valve. Turn clockwise to increase
bypass pressure. If this does not correct the problem, return the relief valve
to the original position. Proceed with step #2.
2
Hydraulic pump failure. Disconnect the pressure hoses at the motor inlet
swivel. Cap the hose. Plug the swivel. If the system does not have a
pressure gauge, install one at the end of the hose for testing purposes.
Engage the PTO and release the clutch slowly. Hydraulic oil pressure
should reach 2300 - 2500 PSI before the relief valve opens.
3
Hydraulic motor or valve failure. Disconnect the pressure hose from the
pump at the gauge swivel. Connect the pressure hose from the pump to the
motor inlet swivel. Shut control valve. engage the PTO. Start the
compressor. If this does not correct the problem, replace the motor. If this
does correct the problem, replace the valve.
Motor does not turn when
hydraulic valve is closed.
Oil does not reach 2300 -
2500 psi.
1
Compressor is locked up. Disconnect the drive system and try to turn the
compressor by hand. If it cannot be turned, repair the compressor.
2
Hydraulic motor failure. Replace the motor if the compressor is operational.
Motor does not turn when
the hydraulic system is
activated. Relief valve
reached 2300 - 2500 psi.
1
Hydraulic motor is beginning to fail. Replace the hydraulic motor before it
damages the rest of the system.
Excessive noise in
hydraulic pump. Pump
gets very hot.
1
Restrictions in oil hoses and fittings. Check and correct any restrictions.
2
Oil tank vent plugged. Check and clean oil tank vent.
3
Hydraulic oil breakdown. Drain and replace.
Hydraulic system
damages pumps. Oil tank
overflows.
1
Tank too full to allow for expansion. Drain excess oil.
2
Oil tank vent plugged. Check and clean.
NOTE: If your truck has two tanks, the return hose from the top tank to the lower
tank may be restricted.
Oil is cold. Compressor is
started cold and fails to
continue to operate.
1
Compressor started too quickly. Insufficient warm-up causes pump failure.
Replace pump, start compressor, and allow sufficient warm-up time.