Honda AC compressor clutch won’t engage: Common causes

Learn what to check when your Honda AC compressor clutch won’t  engage

When you encounter a Honda AC compressor clutch that won’t engage, the problem could be 1) a low refrigerant charge, 2) a failed AC compressor thermal protector, or 3) a faulty AC clutch relay.

Where to start your diagnostics

1) Check AC pressure: The low side pressure must be high enough to over-ride the low-pressure cut-off switch, which is usually calibrated to prevent clutch engagement if pressure is below 35 psi.

2) Check continuity on the AC thermal protector: The thermal protector must show continuity for the AC clutch to engage. The AC thermal protector is located on the compressor. When the compressor overheats, the thermal protector opens, preventing power from reaching the clutch. To test, disconnect the connector and test the thermal protector using a continuity feature on your meter. Replace if necessary,

3) Check for power and ground to the thermal protector connector if the thermal protector shows continuity.

The HVAC head provides a 12-volt reference on the blue/white wire and looks for a return on the red/white wire. If you don’t see that, check for an open between the HVAC control head and the thermal protector connector.

If the HVAC head sees a return voltage, it sends a digital signal to the PCM to power the AC compressor clutch relay. Remember: The blower motor must be running for this to happen.

Check for power to the AC compressor clutch

Disconnect the connector at the AC compressor and test for battery voltage with the engine running, AC ON, and blower ON. If you don’t see battery voltage, check fuses 22 and 25 in the underhood fuse box. If both are good, swap the AC compressor clutch relay. If that works, the problem was a bad relay. If it doesn’t work, remove the relay and check the socket terminals for battery voltage on terminals B7 and B1 and PCM ground on terminal B8

©, 2021 Rick Muscoplat