HVAC Control Power and Ground Circuit Troubleshooting (With A/C)

HVAC Control Power and Ground Circuit Troubleshooting

1. Check the No. 54 (30 A) fuse in the main under-hood fuse/relay box, and the No. 20 (7.5 A) and No. 25 (7.5 A) fuses in the under-dash fuse/relay box.

Are the fuses OK?
YES - Go to step 2.

NO - Replace the fuse(s), and recheck. If the fuse(s) blow again, check for a short in the No. 54 (30 A), the No. 20 (7.5 A), and the No. 25 (7.5 A) fuse circuits.


2. Disconnect the HVAC control unit 30P connector.

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

4. Measure the voltage between HVAC control unit 30P connector terminal No. 30 and body ground.

Is there battery voltage?
YES - Go to step 5.

NO - Repair open in the wire between the No. 20 (7.5 A) fuse in the under-dash fuse/relay box and the HVAC control unit.






5. Turn the ignition switch to LOCK (0).

6. Measure the voltage between HVAC control unit 30P connector terminal No. 29 and body ground.

Is there battery voltage?
YES - Go to step 7.

NO - Repair open in the wire between the No. 25 (7.5 A) fuse in the under-dash fuse/relay box and the HVAC control unit.






7. Check for continuity between HVAC control unit 30P connector terminal No. 26 and body ground.

Is there continuity?
YES - Check for loose wires or poor connections at the HVAC control unit 30P connector. If the connections are good, substitute a known-good HVAC control unit , and recheck. If the symptom/indication goes away, replace the original HVAC control unit.

NO - Check for an open in the wire between the HVAC control unit and body ground. If the wire is OK, check for poor body ground at G402.