I just bought the truck a few weeks ago with 100,000 miles and the A/C was working perfectly. Replaced the timing belt, and A/C still worked flawlessly. Drove about 400 miles yesterday, A/C worked fine during the entire trip.

This morning I turned on the heater while I was loading luggage into the truck. Drove for 10-15 miles with the heater on, then turned it off and hot air kept coming off the vents. Moved the recirc switch and the air still came in very hot no matter what. Decided to turn it off thinking maybe the system got too hot. After 50 or so miles with the A/C off, I turned on the A/C (cold air) and I would still get hot air. (Temp switch now on blue area) I was driving at a speed of 75MPH on average, outside air was cold, and I would still get hot air through the vents. Tried switching back and for from recirc to outside air, played with the temp switch, but the air still comes in very warm. What could be happening?

 

Check to make sure that your heater cable is actually working the heater valve. If it got stuck open while you were using your heat, that might explain your problem.

 

is the heater valve below the dash on the passenger side?

I moved it and it doesn't look stuck, but I guess I'll have to wait until the engine is hot again to test if it's fixed.

 

I found out that the cable that moves the heater valve must be broken or loosened. It seems like it happened inside the AC control unit. Can this be repaired or serviced?

 

well when you drive my 98 4runner and most older cars dont completely seal so air keeps flowing into the intake and across the engine warming it up, thus continuing intpo your vehicle warm.. did you try to turn it to cool then turn the fan up.. cause if i have my fan off and the engine is warm the air comes through slow but hot.... but i click the fan on and the hot-cold works