785G Off-Highway Truck/Tractor Electrical and Hydraulic Systems Caterpillar

The following problem-solving section is provided for identifying and correcting problems that may occur in the heating system. Several problems can have the same system condition (symptom) or similar system conditions. Before you start the procedure to correct the problems, evaluate the performance using the Testing and Adjusting, UENR4125, "Heater Performance –Test". Be complete in the diagnosis of the problem. Repair the components or replace any damaged component if the components are faulty during the inspection.

Symptom: There is little or no warm air that is flowing to the cab when the heater control knob is set to maximum heat.

Possible Cause 1

The blower motor is not working.

1. Inspect the circuit breaker or the fuse panel to ensure that there is no open circuit.

2. Visually inspect the wire harnesses to check for any broken wires or missing connectors. Use the electrical schematic for the respective machine to ensure proper connections.

3. Check the fan blade to make sure that the fan blade is not blocked or seized.

4. Check for the proper function of the fan switch at each setting. The blower motor should engage at all settings and temperatures.

Possible Cause 2

There is a leak that is present in the system.

1. Check the hose clamps making sure that the clamps are present and tightened to the correct torque value that is shown on the drawing.

2. Check the heater coil for any visible cracks or signs of a leak.

3. Check the water valve to make sure that the water valve is properly installed and operational.

Possible Cause 3

The inlet/outlet ports for the engine cooling system are closed.

1. Inspect the valves that connect the heater hoses to the engine block.

2. Make sure that the valves are adjusted so that the valves are fully open.

Possible Cause 4

The hose that is connecting the system together is kinked or blocked.

1. Check for blockage or bends in the hoses. Blockages and bends in the heater hoses restrict the flow of coolant and the blockages reduce the performance of the entire heating system.

2. Replace any hoses that appear to be restricting the flow of coolant.

Possible Cause 5

There is a failure with the device for the heater control.

1. Determine the type of controlling device that is used on the machine.

2. If there is a water valve that is present, continue to Step 3.

3. Inspect the water valve for any signs of damage.

4. Check the water valve making sure that the valve opens completely when the temperature control knob is set to maximum heat.

5. If the water valve fails to open or the water valve fails to close, move to "Possible Cause 6".

Possible Cause 6

There is a failure with the cable for the water valve or the potentiometer.

1. Determine the type of control for the water valve that is being used on the machine.

2. If the machine has a built-in potentiometer, continue to Step 3.

3. Check the machine to make sure that the potentiometer is attached to the wire harness within the dash of the cab.

4. Check the water valve making sure that the valve opens completely when the temperature control knob is moved to maximum heat.

Symptom: The heat that is within the cab is uncontrollable.

Possible Cause 1

The water valve is installed incorrectly or backward.

1. If the machine is equipped with a water valve control, check the valve making sure that the valve is installed properly.

2. Some water valves are manufactured so that there is an arrow that shows the flow direction on the side of the valve body. Make sure that the arrow is pointed toward the line that leads to the heater coil.

3. If the machine is equipped with an electronically driven water valve, make sure that the actuator is attached securely to the water valve.

Possible Cause 2

There is an electrical failure with the control panel.

1. Inspect the control panel to make sure that the control panel is receiving power when the machine is turned on.

2. Check to make sure that the wire harness is connected to the control panel.

3. Use Cat^® ET to check the percentage of the temperature dial.

Possible Cause 3

There is a failure with the potentiometer.

1. Check to make sure that the potentiometer is attached to the wire harness within the dash of the cab.

2. Check to make sure that the water valve opens completely when the temperature control knob is moved to the position of maximum heat.

Symptom: There is a coolant smell that is present within the cab.

Possible Cause 1

There is a leak that is present at the hose or the hose clamps.

1. Inspect the connections between the heater coil and the heater hoses.

2. Check the hoses for cuts.

3. Check to make sure that the hose clamps are tightened to the proper torques that are shown on the dimension drawings.

Possible Cause 2

There is a leak that is present at the heater coil.

1. Inspect the heater coil to determine if there are any visible cracks or holes in the tubing.

2. Check to make sure that the hose clamps are tightened to the proper torques.

Possible Cause 3

There is a leak that is present at the water valve.

1. Inspect the water valve for any damage.

2. Check to make sure that the hose clamps are tightened to the proper torques.

3. If the water valve passes both these initial tests, refer to the Troubleshooting, UENR4125, "Machine Preparation For Testing and Adjusting".

Symptom: There is no flow of air to the operators compartment. The evaporator blower motors do not operate when the fan switch is activated.

Probable Cause 1

There is an open circuit.

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Illustration 1	g06246473

1. Inspect the circuit breaker or inspect the fuses for an open circuit.

2. Use Cat^® ET to check the dial position of the blower and the blower command.

Probable Cause 2

There is a blockage in the fan blades.

1. Check for blockages at the fan blades.

Probable Cause 3

The motor has failed.

1. Make necessary repairs or replace motors and components.

2. After a new motor or blower wheel is installed, inspect operation for the correct rotation.