A/C Signal Circuit Troubleshooting
A/C Signal Circuit TroubleshootingNOTE:
- Use this troubleshooting procedure if the A/C compressor, the A/C condenser fan, and radiator fan are inoperative.
- Before doing symptom troubleshooting, check for and resolve any powertrain DTCs.
1. Turn the ignition switch to ON (II).
2. Check if the blower motor operates at all speeds.
Does the blower motor operate at all speeds?
YES - Go to step 3.
NO - Repair the problem in the blower motor circuit.
3. Turn the ignition switch to LOCK (0).
4. Disconnect the HVAC control unit 28P connector.
5. Turn the ignition switch to ON (II).
6. Measure the voltage between the HVAC control unit 28P connector No. 10 terminal and body ground.
Is there voltage?
YES - Go to step 13.
NO - Go to step 7.
7. Turn the ignition switch to LOCK (0).
8. Disconnect the A/C compressor clutch 3P connector.
9. Turn the ignition switch to ON (II).
10. Measure the voltage between the A/C compressor clutch 3P connector No. 1 terminal and body ground.
Is there battery voltage?
YES - Go to step 11.
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.
11. Test the A/C compressor thermal protector.
Is the A/C compressor thermal protector OK?
YES - Go to step 12.
NO - Replace the A/C compressor thermal protector.
12. Check for continuity between the HVAC control unit 28P connector No. 10 terminal and the A/C compressor clutch 3P connector No. 2 terminal.
Is there continuity?
YES - Check for loose wires or poor connections at the HVAC control unit 28P 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.
13. Turn the ignition switch to LOCK (0).
14. Measure the evaporator temperature sensor resistance between the HVAC control unit 28P connector No. 9 and No. 19 terminals.
Is the resistance less than 24 Kohms?
YES - Check for loose wires or poor connections at the HVAC control unit 28P connector. If the connections are good, substitute a known-good HVAC control unit, and recheck. If the symptom goes away, replace the original HVAC control unit.
NO - Test the evaporator temperature sensor.