A/C Signal Circuit Troubleshooting
A/C Signal Circuit Troubleshooting1. Turn the ignition switch OFF.
2. Disconnect the A/C compressor 3P connector.
3. Turn the ignition switch ON (II).
4. Measure voltage between ECM connector terminals A24 and E28.
Is there about 5 V?
YES - Go to step 5.
NO - Go to step 13.
5. Turn the ignition switch OFF.
6. Reconnect the A/C compressor 3P connector.
7. Turn the ignition switch ON (II).
8. Momentarily connect ECM connector terminals A5 and E18 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 17.
9. Remove the jumper wire from the ECM connectors.
10. Start the engine.
11. Turn the blower switch ON.
12. Turn the A/C switch ON.
Does the A/C operate?
YES - The A/C switch signal is OK.
NO - Check the A/C system.
13. Turn the ignition switch OFF.
14. Wait for 1 minute. If the radiator fan is running, wait for 1 minute after the radiator fan stops.
15. Disconnect ECM connector E (31P).
16. Check for continuity between ECM connector terminal E28 and body ground.
Is there continuity?
YES - Repair short in the wire between the ECM (E28) and the A/C compressor.
NO - Update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM.
17. Momentarily connect under-hood fuse/relay box 14P connector terminal No. 10 to body ground with a jumper wire several times.
NOTE: The under-hood fuse/relay box 14P connector is on the bottom of the fuse box. When you unbolt and invert the fuse box, leave the upper cover on it to prevent a short circuit.
Is there a clicking noise from the A/C compressor clutch?
YES - Repair open in the wire between the ECM (E18) and the A/C compressor clutch relay.
NO - Check the A/C system for other symptoms.