Symptom: When the heater control knob is turned to the hottest position, there is little or no heat flow to the cab.
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The following problem-solving information is intended for locating and correcting problems in heating systems. Different problems may cause the same or similar system conditions (symptoms). Refer to Testing and Adjusting, SENR 5664, "Heater Performance - Tests" to evaluate system performance before beginning the corrective procedures. The problem must be diagnosed first. If any parts are found damaged during inspection, repair or replace them.
Symptom: When the heater control knob is turned to the highest setting, little or no heat flows to the cab. Possible Cause 1 The blower motor is not operating. 1. Check the circuit breaker or fuse box to ensure there are no open circuits in the system. 2. Visually inspect the wiring harness for damaged wires and missing connectors. Refer to the electrical schematic for each machine to ensure proper connections. 3. Inspect the fan blades to ensure they are not obstructed or stuck. 4. Check that the fan switch operates properly at all settings. The blower motor should operate at a variety of settings and temperatures.
Possible Cause 2 There is a leak in the system. 1. Check the hose clamps to ensure they are not missing and are tightened according to the torque values shown in the diagram. 2. Check the heating coil for any visible cracks or leaks. 3. Check the water valve to ensure it is installed correctly and is functioning properly.
Possible Cause 3 The engine cooling system's inlet/outlet is closed. 1. Check the valve connecting the heater hose to the engine block. 2. Ensure the valve is fully open.
Possible Cause 4 The hoses connecting the system are kinked or clogged. 1. Check the hoses for blockages or bends. Blockages and bends in the heater hoses can restrict the flow of coolant and reduce the performance of the entire heating system. 2. Replace any hoses that may be restricting coolant flow.
Possible Cause 5 The heater's controls are malfunctioning. 1. Determine the type of controls used on the machine. 2. If the system is equipped with a water valve, proceed to step 3. If the system is equipped with a blend door, proceed to step 6. 3. Inspect the water valve for signs of damage. 4. Inspect the water valve to ensure that it fully opens when the temperature control knob is set to the hottest position. 5. If the water valve will not open or close, proceed to "Possible Cause 6." 6. Inspect the blend door. 7. Inspect the blend door for any damage. 8. Ensure that the insulation on the blend door is intact. 9. Ensure that the actuator is connected to the blend door. 10. Inspect the blend door to ensure that it fully opens when the temperature control knob is set to the hottest position.
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Possible Cause 6 The water valve cable or potentiometer is faulty. 1. Determine the type of water valve control used on the machine. 2. If the water valve has a cable connected, proceed to step 3. If the machine has a built-in potentiometer, proceed to step 5. 3. Inspect the machine to ensure that the cable is connected to the water valve handle. 4. Inspect the water valve to ensure that the water valve is fully open when the temperature control knob is set to the hottest position. 5. Inspect the machine to ensure that the potentiometer is connected to the wiring harness in the cab instrument panel. 6. Inspect the water valve to ensure that the water valve is fully open when the temperature control knob is set to the hottest position.
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