96 Explorer XLT AWD will only blow out cold air. Temp. pot switch on one day when turned to cold side blow out hot air. **** turned loosely. Now all I get is cold air. Changed temp. pot switch. New switch seems to function, because I get very cold air when all the way turned left or cold side and luke-warm air when turned all the way to the right or Hot side. But no hot air. The vacuum control value under the hood on top of the heater fan housing moves in and out when the system is turned on and off. Fan selector switch seems to funtion on all the speeds. And the Air duct direction/AC selector switch seems to function OK. What other things can I check?
Also is the AC suppost to always run with this system?
Thanks

 

check the coolant level, thermostat, and heater core. that is what my dad had to do when his went out on his explorer

 

Explorers have a huge problem with the blend doors breaking causing them not to change from hot to cold and vice versa. There's a thread on a repair for this problem in the Explorer section that might be worth looking into. Dealerships will charge for a new plenum and the labor to remove the dashboard. The other repair looks pretty slick, but I haven't tried it yet.