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 PCM connector terminals A27 and B20.
IS there approx. 5 V?
YES - Go to step 5.
NO - Go to step 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 PCM connector terminals A17 and B20 with a jumper wire several times.
Is there a clicking noise from the A/C compressor clutch?
YES - Go to step 9.
NO - Go to step 15.
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.
NO - Go to step 12.
12. Turn the ignition switch OFF.
13. Disconnect the PCM connector A (32P).




14. Check for continuity between body ground and PCM connector terminal A27.
Is there continuity?
YES - Repair short in the wire between PCM (A27) and the A/C pressure switch.
NO - Substitute a known-good PCM and recheck. If prescribed voltage is now available, replace the original PCM. If not, check the A/C symptom for other symptoms.
Diagnostic Strategies




15. Momentarily connect the under-hood fuse/relay box 16P connector terminal No.11 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 PCM (A17) and the A/C clutch relay.
NO - Check the A/C symptom for other symptoms.




16. Measure voltage between PCM connector terminal A27 and B20.
Is there less than 1.0 V?
YES - Substitute a known-good PCM and recheck. If the symptom/indication goes away, replace the original PCM. If not, check the A/C symptom for other symptoms.
Diagnostic Strategies

NO - Repair open in the wire between the PCM (A27) and the A/C pressure switch.