what causes the air conditioner and heat to suddenly stop working?? on 1999 Ford F-150

one ac works fine next day just blows hot air switched to heat and still blowing same temp air. now its cold out and cant get any hot air same temp air in ac or heat. climate control knob not stripped blend door doesnt move when changing temp but doesnt seem to b broke

Asked by for the 1999 Ford F-150
2 answers
Change the blend door actuator if blend door is not moving.
you may have a couple of issues,poss low freon level and coolant level.start there. after that could be a multi. of isssues