Hydraulic System Troubleshooting - Blue Bird TC/2000 Owner's Manual

HYDRAULIC SYSTEM - TROUBLESHOOTING
1. Hydraulic fan will not run.
A. Check hydraulic oil level in reservoir. (Sight glass)
B. Check fan motor for free rotation, fan motor should rotate freely. If not rebuild or replace fan
motor.
CAUTION: Engine should be shut off when checking fan motor for free rotation.
C. Disconnect wires from relief valve solenoid or temperature control switch, and start engine. If fan
runs with wire disconnected, the temperature control switch is at fault. Replace switch. If fan does
not run with wire disconnected, the solenoid valve may be at fault. Repair or replace solenoid
valve. If this does not correct the problem proceed with the following steps.
D. With hydraulic system at normal operating temperature check pump output pressure to specifica-
tions below. Check pressure with wires disconnected from relief valve solenoid, or temperature
control switch.
Note: A pressure tap can be installed at port marked "PR" on the relief valve.
ENGINE
5.9 Cummins
8.3 Cummins
E. If pressure is low, adjust the pressure relief adjustment screw by loosening the jam nut and turn-
ing the adjustment screw clockwise to increase pressure. If the pressure comes up to specifica-
tions, and the fan speed doesn't, the fan motor has excessive internal leakage and is at fault. Repair
or replace fan motor. If specified pressure is obtained, the relief valve is at fault. Repair or replace
relief valve.
F. If after adjusting the pressure relief screw the pressure does not come up to specification, the
pump may be at fault, repair or replace pump.
NOTE: If pump is faulty it is also likely the power steering will show signs of low pressure.
2. Fan motor runs continuously.
A. Check for 12 volts at the relief valve solenoid. Solenoid will not operate properly with less than 12
volts.
B. If check shows 12 volts at solenoid, solenoid or solenoid valve may be faulty. Repair or replace
solenoid or solenoid valve.
C. If check shows no voltage at solenoid, check voltage supply at temperature control switch. If check
shows 12 volts at temperature control switch, switch is at fault, replace switch. If check shows no
voltage, check circuit breaker and all connections, short in circuit or open circuit.
3. Fan motor runs under speed.
A. Check engine speed at idle and full RPM.
B. See Steps 1-D, thru 1-F.
4. Shaft seal leak on pump is recognized by excessive addition of hydraulic oil, or in the Cummins 5.9T,
and overfilled condition of the engine crankcase. Replace shaft seal or pump. Change engine oil.
PUMP PRESSURE (PSI)
100-300
2000
2450
ENGINE RPM
800
2500
2400
78
FAN RPM
200
1900
1950