My 1996 850 GLT Wagon has gotten to be a cold brick on these last few days when the temps don't climb above single digits.

The temperature gauge might edge slightly above the bottom tick mark, but falls back almost immediately. Also, the fuel gauge appears to have gotten stuck (tho' that seems to work now after letting the car sit overnight).

What is really frustrating is that the cabin doesn't warm up and near-zero outside temps translate rather quickly to numb hands on the wheel.

Odd thing is that all seems to function when the exterior temps were in the 20's. Or isn't this an odd thing?

Car has about 80k on the odometer.

Is this likely to be the thermostat, the sensor, both? What are the diagnostics (I will have to check the REC and AC lights, but I hadn't noticed anything).

Thanks,
Scott