I found this disconnected sensor on the HVAC duct. You can see that the wires have been jumpered instead. I suspect this is the anti-freeze temp sensor but don’t know why it has been bypassed. The A/C has been repaired recently including expansion valve replacement. Can someone verify my suspicion and tell me how to test the sensor? I want to know if it works before I reconnect it.



Thanks in advance.

 

Yes, that is the A/C anti-freeze switch.

You can remove the switch - be careful pulling the sensor capillary tube out of the evaporator fins.

Put the capillary tube into a class of ice water. The switch should be open at or below 32 deg F, closed above 32 deg F.

Some of the earlier switches were adjustable - yours does not appear to be (no slot in the central screw).

 

Thanks Wally.

The capillary tube came out easily and the sensor tested OK.

Is there a trick to getting the capillary tube back in? I can't seem to find a place where the tube will slide in easily. I'm worried about damaging the evaporator fins.