Ambient Temp Slowly Rising
 

Hello,
I have a 2002 Millenia-s
Something very strange is happening with my climate control system. It started 3 or 4 days ago. I'll explain a well as I can:
When I first start the car up, the ambient temperature displays correctly. For instance, yesterday it showed as 34 Degrees F.
Over the course of my drive, which yesterday was about 1.5 hours, the ambient temp rose slowly, about 1 degree per minute, until it reached the max of 99 degrees towards the end of the trip. Along the way, I had to keep bumping up the interior temp so keep the heat running. This has been happening every time I drive the car since it started.
The engine temperature is fine, and there are no warning lights.
There is plenty of coolant in the reservoir.
I have a feeling that, because of the slow rise in the reading, that the sensor itself may not be the problem - that something else is causing it to heat up like that. I'm not sure where it is located - front bumper??
I would appreciate any assistance with this - maybe someone has encountered this before.
Thanks!