797B Off-Highway Truck Fan Drive Hydraulic System: Piston Pump (Fan Drive) Pressure - Test and Adjust

The following tests cover the setting of the following valves:

• Pressure and flow compensator valve
• High pressure cutoff valve

Table 1

Required Tools
Tool	Part Number	Part Description	Qty
A	8T-0860	Pressure Gauge	1

Fan drive pump (1) Pressure and flow compensator valve (2) Displacement solenoid and valve (3) High pressure cutoff valve/Pressure override(4) Current adjustment screw

The pressure and flow compensator valve (1) is mounted to the case of the fan drive pump. The fan drive pump is mounted to the steering pump. The steering pump is mounted to the pump drive. The pump drive is located on the inside of the right frame rail near the torque converter.
If problems are suspected, the first step is checking the override pressure for the pump. Make sure that the override pressure is correct. The following procedure should be performed before running any of the fan tests at full speed in order to ensure that fan overspeed does not occur.
Note: Maximum pressures may need to be set differently at high altitudes to avoid possible fan overspeed and damage.
In order to determine the correct high pressure cut-off setting for the altitude of the truck,follow the procedure below. Use ET to override the hydraulic fan drive to 525 rpm. Raise the engine speed to high idle. Record the pump pressure and the fan speed. The high pressure cut off valve for the pump should be set at a minimum of 2070 kPa (300 psi) above the pressure that is required in order to maintain the maximum fan speed of 525 rpm. The solenoid must be unplugged.

1. Shut off the engine.

2. Remove the pressure hose from the output port of the pump and install a blocking plate with a tap on the pump outlet port. Block the high pressure hose that is opened as well. Install Tool (A) on the pressure tap on the blocking plate.

3. Disconnect the displacement solenoid from the main wiring harness.

4. Start the engine and observe the pressure. The override pressure depends on the altitude. The pressure at sea level should be 22750 kPa (3300 psi).

Pressure And Flow Compensator Valve

Displacement Solenoid And Valve

(2) Displacement solenoid and valve (4) Current adjustment screw(5) Locknut

Note: There is no procedure for adjusting the current adjustment screw (4) at this time.
Note: There are two methods that can be used to view fan speeds:

• Use the Electronic Technician (ET) and view the data with the VIMS display window.
• Use the Electronic Technician (ET) and a laptop computer that is installed with VIMS-PC software.

Note: If the third method is selected, a 140-9442 Adapter Cable will allow the connection of two communication adapters.


1. Install the Electronic Technician (ET) onto a laptop computer and connect the laptop computer to the machine in order to override the fan speed. Refer to Special Instruction, NEHS0717, "Caterpillar Electronic Technician User Manual For Customers" for more information on the use of the Electronic Technician (ET).

2. Start the engine.

3. Check the fan drive pump pressure by installing Tool (A) to the pressure tap that is located by the makeup valve. The fan drive pump pressure should be between 0 to 22750 kPa (0 to 3300 psi). The pressure will vary depending on the desired fan speed that is set by the Brake/Cooling ECM.

4. Use the following procedure in order to configure a group of parameters within ET, that will be monitored.
   
   
   1. On the ET screen, select Datalink. From the ECM list, choose the Brake ECM.
   
   
   2. From the Status Group, create a new group that is called Fan Test.
   
   
   3. The following parameters should be inserted into the Fan Test from the Transmission ECM: Transmission Oil Temperature and Torque Converter Outlet Temperature.
   
   
   4. The following parameters should be inserted into the Fan Test from the Brake ECM: Brake Oil Temperature (Right Rear), Desired Engine Fan Speed, Engine Fan Speed and Engine Speed.
   
   
   5. The following parameters should be inserted into the Fan Test from the Engine Front Module ECM: Engine Coolant Temperature and Rear Aftercooler Temperature.

5. With cold temperatures, no service brakes and the engine at low idle, the fan drive pump will not be energized. The fan speed and the fan drive pump pressure should be close to zero. At high idle, the fan drive pump pressure will also be close to zero.

6. The following procedure will be used to override the fan speed. During the test, the fan speed will be overridden at 300 rpm, 400 rpm and 525 rpm.
   Note: When the engine speed is changed from low idle to high idle, the fan drive pump will produce a hydraulic pressure spike while the fan begins to rotate. The fan drive pump pressure will begin to even out.
   
   
   1. On the ET screen, select Diagnostics. Select Override Parameters.
   
   
   2. Select "Desired Engine Cooling Fan Speed Override" and change the value to the required rpm.

7. With the engine at low idle, override the fan speed to 300 rpm, 400 rpm and 525 rpm. Monitor the fan drive pump pressure at each interval and record the pressures.

   Table 2

   Fan Drive Pump Pressures These pressures are at sea level.
   RPM	Pressure
   300	8300 kPa (1200 psi) (1)
   400	15500 kPa (2250 psi)
   525	21000 kPa (3050 psi)

   ( 1 )

   The pressure will vary depending on the altitude, the temperature, and the barometric press as well as other factors.

   
   Note: If the fan drive pump pressures are incorrect, check for bearings that are too tight, improper operation of the fan drive motor and improper operation of the fan drive pump.

High Pressure Cutoff Valve

(1) Pressure and flow compensator valve (2) Displacement solenoid and valve (3) High pressure cutoff valve (6) Setscrew(7) Locknut

1. Connect Data View or a gauge to the machine in order to view the fan drive pump pressure. Refer to Tool Operating Manual, NEHS0662, "Caterpillar Data View" for more information on using DataView.

2. Disconnect displacement solenoid (2) at the electrical connection.

3. Start the engine.

Note: When the engine speed is changed from low idle to high idle, the fan drive pump will produce a hydraulic pressure spike while the fan begins to rotate. The fan drive pump pressure will begin to even out.
Note: The setting of the high pressure cutoff valve must be set lower at higher altitudes. At 3142 m (10300 ft), only 15158 kPa (2200 psi) is required to maintain a fan speed of 525 rpm.


4. The fan will overspeed if the following conditions exist:
   
   • the engine is operating at high idle.
   • the setting of the high pressure cutoff valve is too high.
   • the displacement solenoid is disconnected.
   A fan overspeed error occurs at approximately 541 rpm.

5. In order to adjust the setting of the high pressure cutoff valve, install a blocker plate in the pump outlet port. Disconnect the displacement solenoid. With the engine at low idle, the fan drive pump will destroke and the fan drive pump will operate at minimum flow and at maximum pressure.

6. Loosen locknut (7) on high pressure cutoff valve (3). Rotate setscrew (6) clockwise in order to raise the pressure. Rotate setscrew (6) counterclockwise in order to lower the pressure.

7. Repeat Steps 4 and 6 until the desired pressure setting is reached.

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797B Off-Highway Truck Fan Drive Hydraulic System: Piston Pump (Fan Drive) Pressure - Test and Adjust 2013-01-25T20:07:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown