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| Illustration 1 | g06020345 |
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Typical HVAC Components | |
The "Automatic Temperature Control (ATC)" system includes all the standard HVAC components for manual temperature control along with the louver and recirculation temperature sensors.
To enable the ATC function, follow the steps below:
- Select the AUTO position on the mode selection switch on the control.
- Rotate the temperature dial to the desired temperature setting.
- Rotate the blower fan dial to the desired speed.
Note: There has to be some fan speed for the ATC to operate. Full CW rotation of the dial will turn the ATC OFF.
The Electronic Control Module (ECM) receives the requested temperature from the control panel and cab temperature sensor and automatically controls the water valve actuator and compressor to reach and maintain that temperature.
Some machines are also equipped with an "Auto Blower" option that adjusts the blower fan speed based on the cab temperature error. The larger the temperature difference the faster the blower fan speed.
Automatic Temperature Control Troubleshooting
Use this procedure to troubleshoot the HVAC system for machines equipped with automatic temperature control.
Connect Cat® Electronic Technician (Cat®ET) and check for diagnostics associated with the HVAC system. Refer to the troubleshooting section for each code if any of the following codes are active.
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| Illustration 2 | g03090916 |
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HVAC Diagnostic Codes | |
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| Illustration 3 | g03090917 |
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Typical HVAC ET status parameters and values | |
- Diagnostic Codes
- Low-Pressure Switch / High-Pressure Switch
- Low Refrigerant Charge
- Water Valve Actuator
- A/C Compressor
3
Connect Cat®ET to the service tool connector. Check for active diagnostic codes. Look for active codes that are related to the HVAC system in Illustration 2. Use the appropriate circuit test to troubleshoot any active codes before continuing.
Low-Pressure Switch / High-Pressure Switch
Use Cat®ET to monitor the "Air Conditioning Refrigerant Monitoring Circuit" status parameter. With a proper charge, the status should be closed. If the status is open, check the pressure switches and circuit. Refer to the pressure switch tests section in this book.
Refer to the HVAC, Air Conditioning System section in this manual.
Test the water value actuator control by switching to HEAT mode. Use Cat®ET and monitor the ""Cab Air Heater Engine Coolant Actuator Duty Cycle"" status parameter while rotating the temperature dial. The parameter should go to 5% when the temperature dial is fully CCW and 95% when the temperature dial is fully CW. If the duty cycle of the "Cab Air Heater Engine Coolant Actuator" does not change in response to the temperature dial, check the temperature dial. (See the troubleshooting section for the DTC 2661). If the duty cycle of the "Cab Air Heater Engine Coolant Actuator" changes in response to the temperature dial, verify the water valve actuator circuit. Verify that the actuator is rotating.
With the engine running, switch to AC mode and use Cat ET to monitor the "A/C Compressor" status parameter. If the compressor status does not turn to ON after 20 seconds, check the evaporation temperature circuit. For the pressure switch circuits, refer to the pressure switch tests section in this manual. If the compressor status is ON and the compressor does not turn ON, check for power at the compressor connection.
Note: If the compressor status is on and there is power at the compressor clutch, replace the compressor.
- Diagnostic Codes
- Water Valve Actuator
Connect Cat ET to the service tool connector. Check for active diagnostic codes. Look for active codes that are related to the HVAC system in Illustration 2. Use the appropriate circuit test to troubleshoot any active codes before continuing.
Test the water value actuator control by switching to HEAT mode. Use Cat®ET and monitor the "Cab Air Heater Engine Coolant Actuator Duty Cycle" status parameter while rotating the temperature dial. The parameter should go to 5% when the temperature dial is full CCW and 95% when the temperature dial is full CW. If the"Cab Air Heater Engine Coolant Actuator Duty Cycle" does not move with the temperature dial, check the temperature dial. check the temperature dial. See the troubleshooting section for DTC 2661 in this manual. If the "Cab Air Heater Engine Coolant Actuator Duty Cycle" moves with the temperature dial, verify the water valve actuator circuit. Verify that the actuator is rotating.