COVER 9J4776 - Caterpillar

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).Low Refrigerant Charge
Refer to Air Conditioning Performance - TestWater Valve Actuator
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 duty cycle of the "Cab Air Heater Engine Coolant Actuator" does not change in response to the temperature dial, check the temperature dial. 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.A/C Compressor
Switch to AC mode and use CatET to monitor the "A/C Compressor" status parameter with the engine running. If the compressor status does not turn to ON after 20 seconds, check the evaporation temperature circuit. (Refer to 2357 diagnostic code in "Sensor Signal (Analog, Passive - Test")). 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, then replace the compressor.Cab Temperature Low
Probable Causes
Diagnostic Codes
Water Valve ActuatorRecommended Actions
Diagnostic Codes
Connect CatET to the service tool connector. Check for active diagnostic codes. Look for active codes that are related to the HVAC system in Illustration 1. Use the appropriate circuit test to troubleshoot any active codes before continuing.Water Valve Actuator
Test the water value actuator control by switching to heat mode. Use Cat®ET and monitor the duty cycle for the "Cab Air Heater Engine Coolant Actuator" 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 duty cycle for the "Cab Air Heater Engine Coolant Actuator" does no't move with the temperature dial, check the temperature dial. (See the troubleshooting in the "Switch Circuits - Test" section of this manual). If the duty cycle of the "Cab Air Heater Engine Coolant Actuator" moves with the temperature dial, verify the water valve actuator circuit. Verify that the actuator is rotating.No Airflow from Evaporator Blower Motor
No Auto Blower Control
Illustration 3 g03417195
Illustration 4 g03543956Perform this test with the key on. Use a 5P-7277 Voltage Tester or use a 257-9140 Digital Multimeter and connect the negative probe to the pin 7 wire on the control panel