Well...This just happened to me. Outside temps were ~36, threw a Chick-fil-A wrap in the cool box and sidearm was shoved between the seat and center console. After a few hours, heat was radiating from the seat (thought the seat heater was on), sidearm was HOT, and eventually opened the cool box to get the wrap and noticed hot air blowing.
I was really confused since the AC was on and functioning normally.
I went to some dark places like TC overheating or some random circuit about to catch fire. Glad I found this thread!
If you were in the 80 series forum, everybody would have said you have a blown head gasket. So, I guess you got that going for ya.