There are 3 ECT sensors mounted on the thermostat housing. One has 4 pins, and AllDataDIY clearly identifies that as the ECT for the engine computer. The second has a single pin, and the third has two pins.

Digging through AllDataDIY reveals that the errors logged by the HVAC control for an error relating to the ECT refer to component 10/8 (I think). However, when you dig up the location of that item, it's not listed - grrr. I think I've been down this road before. (I haven't checked to see what errors are stored by the control unit).

I've gotten the resistance values for the ECT from the diagnostic charts. When I have a minute, I'll compare those values with the values for the two sensors and see if either one of them is faulty.

I'm sure that the single-pin sensor is reference to ground. I'll hazard a guess that the double-pin sensor is reference between the two pins.

I also answered one of my earlier questions while digging through the error codes for the HVAC control - it does log short or open circuits as errors. So, if the sensor is connected but shorted to ground, that's an error. Disconnecting the sensor entirely will also be an error, and I'll bet that both errors result in the same behavior - namely no A/C.

Thanks for your input. I'll let the board know what I find out.

Regards