## A/C Signal Circuit Troubleshooting

1. | Turn the ignition switch OFF.

2. | Disconnect the A/C pressure switch connector.

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

4. | Measure voltage between ECM/PCM connector terminals A24 and E28. Is there approx. 5V? YES - Go to 5. NO - Go to 12.

5. | Turn the ignition switch OFF.

6. | Reconnect the A/C pressure switch connector.

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

8. | Momentarily connect ECM/PCM connector terminals A24 and E18 with a jumper wire several times. Is there a clicking noise from the A/C compressor clutch? YES - Go to 9. NO - Go to 16.

9. | Start the engine.

10. | Turn the blower switch ON.

11. | Turn the A/C switch ON. Does the A/C operate? YES - The air conditioning signal is OK.n NO - Go to 17.

12. | Turn the ignition switch OFF.

13. | Disconnect the negative cable from the battery.

14. | Disconnect ECM/PCM connector E (31P)

15. | Check for continuity between body ground and ECM/PCM connector terminal E28. Is there continuity? YES - Repair short in the wire between the ECM/PCM (E28) and the A/C pressure switch.n NO - Substitute a known-good ECM/PCM and recheck. If prescribed voltage is now available, replace the original ECM/ PCM. If not, check the A/C system for other symptoms.n

16. | Momentarily connect the A/C compressor clutch relay 4P connector (into the under-hood fuse/relay box) terminal No. 3 to body ground with a jumper wire several times. Is there a clicking noise from the A/C compressor clutch? YES - Repair open in the wire between the ECM/PCM (E18) and the A/C clutch relay.n NO - Check the A/C system for other symptoms.n

17. | Measure voltage between ECM/PCM connector terminals A24 and E28. Is there less than 1.0 V? YES - Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/ PCM. If not, inspect the air conditioning system.n NO - Repair open in the wire between the ECM/PCM (E28) and the A/C pressure switch.n