I am assuming that "temperature outside is in the 20's" means 20 degrees Celcius (Centigrad)?

Question; have you tried turning on the heater and running the fan at full blast? If so does it drop the temp considerably? Is the air out of the vents extremely hot?

If yes, turn off the ignition, pop the hood and try to move the fan by hand. If it moves easily, as other have said, your fan clutch is bad. Hope that the clutch and blades are seperate (likely). You can tell because the fan blades are plastic. Cheap part, easy repair.

If no, your quest is more difficult. It could (likely) be the voltage compensation board (if that year had one) or a bad ground for the dash. It also could be a bad temp sensor. If the vents blew hot air, those are the two most likely possibilities.

Onkel Udo