Hydraulic System
3
5. Clean the switch valve relief valve to make sure that nothing is holding it open. Follow these
steps:
a. Stop the engine.
b. Unscrew the relief valve cap (Figure 8-
4
).
c. Remove the bonded washer, spring, and poppet, taking care not to dislodge the shims which
are between the spring and cap.
d. Check that the relief valve seat is clean and free from dirt. Wash the relief valve poppet in a
clean solvent and examine for cracks or other damage.
e. Replace the relief valve, making sure that no contaminant is introduced into the valve. Care
should be taken to replace the original number of shims under the relief valve cap.
6. Rerun the above test. If the fan still runs at idle speed replace the switch valve assembly. If upon
replacement of the switch valve, the fan continues to run at idle speed, the pump or motor may
be severely damaged. Check the hydraulic reservoir for contamination and metal particles.
Fan Runs at “Hot” Speed When Engine is Cold
1. With the engine in the cold condition run at governed speed. Check the fan speed using the photo
tach. If the fan runs at maximum speed stop the engine and check the voltage supply to the fan
control valve to ensure that it is receiving system voltage. Any loss of power or signal to the fan
control valve will automatically run the fan at maximum speed.
2. If all connections to the fan control valve are fastened securely:
a. Disconnect the feed and return lines to the valve.
b. Using a short length of hose, connect the fan control valve feed and return points on the
switching valve together. This removes the pressure differential in the switching valve en-
suring the switch valve will bypass pump flow from the fan motor allowing it to run at idle
speed. Fan idle speed with full engine speed will be about 400 rpm or less. Hydraulic fluid
temperature should not exceed 180° F.
3. With the engine cold run at governed speed, check the fan speed. If the fan runs at idle speed,
this verifies the switch valve is operating correctly.
4. Replace the fan control valve. If this does not correct the problem, check the engine electronic
system to verify that it is sending the correct PWM signal.
Summary of Contents for LOW FLOOR
Page 18: ...Specifications 18...
Page 58: ...Preventive Maintenance 58...
Page 110: ...Engine 110...
Page 138: ...Transmission Driveline Rear Axle 138...
Page 182: ...Suspension 182...
Page 260: ...Air System 260...
Page 420: ...Electrical System 420 Deutsch DT Series Connectors...
Page 421: ...Electrical System 421...
Page 422: ...Electrical System 422 Deutsch HD 10 Series Connectors...
Page 423: ...Electrical System 423...
Page 424: ...Electrical System 424 Deutsch HD 30 Series Connectors...
Page 425: ...Electrical System 425...
Page 442: ...Heating Air Conditioning 442...
Page 492: ...Body and Interior 492 Figure 11 33 USSC Seat Assembly...
Page 493: ...Body and Interior 493 Figure 11 34 USSC Seat Suspension Assembly...
Page 495: ...Body and Interior 495 Figure 11 37 Seat Air Connections...