Yep looked in the slots of mine and there is what looks like the end of a thermal couple setting there

 

I would have to say that if you have the device in place and don't have climate control that they are using it to measure interior air temp for some other reason. Maybe to sense the temp for remote start/auto cab heater/ ac switch over point. But I'm sure there must be some other option that uses the reading besides the climate control

 

Hmmm....maybe we're getting closer. I don't have any of those options. But, one silly thing I've always wanted was a "smart" defrost on a vehicle. Sometimes we defrost a window with cold air in Florida (it's partly a humidity thing) and sometimes we defrost with hot air. If that sensor determines the cab temp and compares it to the exterior temp sensor then it's a step in the right direction toward a "smart" defrost.

 

Living in western pa and frequently in the mountains. We have the same problems with humidity and odd dew points. I've often thought about why the manufactures can't make a defroster that actually knows when and how to defrost the windows

 

Pretty sure it is a humidity sensor for the AC.
If you look under the dash, behind it, there is a little tube running from it to the air box.

 

Tube probably goes to the low pressure side of the air box to induce flow past the sensor.