HVAC Control Unit A/C Signal Circuit Troubleshooting (With A/C)

HVAC Control Unit A/C Signal Circuit Troubleshooting

NOTE:

- Do not use this troubleshooting procedure if any of the following items are operative; A/C condenser fan, radiator fan, A/C compressor. Refer to the symptom troubleshooting index.

- Before performing symptom troubleshooting, check for powertrain DTCs; R18A1 engine, Initial Inspection and Diagnostic Overview K20Z3 engine. Initial Inspection and Diagnostic Overview

- Do not use this troubleshooting procedure if the A/C system pressure is abnormal. Heating and A/C System Description (With A/C)

1. Turn the ignition switch to LOCK (0).

2. Disconnect the HVAC control unit 24P connector.

3. Turn the ignition switch to ON (II).

4. Measure the voltage between the HVAC control unit 24P connector terminal No. 11 and body ground.

Is there voltage?
YES - Go to step 11.

NO - Go to step 5.






5. Turn the ignition switch to LOCK (0).

6. Disconnect the A/C compressor clutch 3P connector.

7. Turn the ignition switch to ON (II).

8. R18A1 engine: Measure the voltage between the A/C compressor clutch 3P connector terminal No. 3 and body ground.
K20Z3 engine: Measure the voltage between the A/C compressor clutch 3P connector terminal No. 1 and body ground.

Is there battery voltage?
YES - Go to step 9.

NO - Repair open in the wire between the A/C compressor and the MICU. If the wire is OK, substitute a known-good MICU and recheck. If the symptom goes away, replace the original MICU. Under-Dash Fuse/Relay Box Removal and Installation


R18A1 engine





K20Z3 engine





9. Test the A/C compressor thermal protector. Testing and Inspection

Is the A/C compressor thermal protector OK?
YES - Go to step 10

NO - Replace the A/C compressor thermal protector. A/C Compressor Thermal Protector Replacement (With A/C)


10. R18A1 engine: Check for continuity between the HVAC control unit 24P connector terminal No. 11 and the A/C compressor clutch 3P connector terminal No. 1.
K20Z3 engine: Check for continuity between the HVAC control unit 24P connector terminal No. 11 and the A/C compressor clutch 3P connector terminal No. 3.

Is there continuity?
YES - Check for loose wires or poor connections at the HVAC control unit 24P connector and at the A/C compressor clutch 3P connector.

NO - Repair open in the wire between the HVAC control unit and A/C compressor.


R18A1 engine





K20Z3 engine





11. Turn the ignition switch to LOCK (0).

12. Measure the evaporator temperature sensor resistance between the HVAC control unit 24P connector terminals No. 2 and No. 13.

Is resistance less than 24 kOhms?
YES - Go to step 13.

NO - Test the evaporator temperature sensor. Evaporator Temperature Sensor Test (With A/C)






13. Reconnect the HVAC control unit 24P connector.

14. Turn the ignition switch to ON (II).

15. Check if the blower motor operates at all speeds.

Does the blower motor operates at all speeds?
YES - Check for loose wires or poor connections at the HVAC control unit 24P connector. If the connections are good, substitute a known-good HVAC control unit Service and Repair and recheck. If the symptom goes away, replace the original HVAC control unit.

NO - Repair the problem in the blower motor circuit.