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A/C Signal Circuit Troubleshooting, HVAC

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. Symptom Related Diagnostic Procedures
- Before doing any symptom troubleshooting, check for powertrain DTCs.

1. Connect the HDS to the DLC.
2. Start the engine.
3. Turn on the A/C.
4. Check the blower motor operates at all speeds.

Does the blower motor operate at all speeds?

YES - Go to step 5.

NO - Repair the problem in the blower motor circuit.

5. Check the A/C SWITCH in the PGM-FI Data List with the HDS.

Is the A/C SWITCH on?

YES - The A/C signal is OK at this time.

NO - Go to step 6.

6. Turn the ignition switch OFF.
7. Disconnect the climate control unit connector A (24P).




8. Measure the evaporator temperature sensor resistance between the climate control unit connector A (24P) terminals No. 13 and No. 18.

Is the resistance less than 24 kohms?

YES - Go to step 9.

NO - Test the evaporator temperature sensor.

9. Turn the ignition switch ON (II).




10. Measure the voltage between the climate control unit connector A (24P) terminal No. 17 and body ground.

Is there battery voltage?

YES - Go to step 11.

NO - Repair open in the wire between the climate control unit and the MICU.

11. Turn the ignition switch OFF.
12. Reconnect the climate control unit connector A (24P).
13. Set the A/C button and fan control switch to ON, then turn the ignition switch ON (II).




14. Measure the voltage between the climate control unit connector A (24P) terminal No. 17 and body ground.

Is there 0.5 V or less?

YES - Replace the MICU.

NO - Check for loose wires or poor connections at the climate control unit connector A (24P). If the connections are good, substitute a known-good climate control unit and recheck. If the symptom/indication goes away, replace the original climate control unit.