It's happened a time or two before, but always seems to 'fix' itself. Last night, of course when it was 20 degrees outside, the driver side would not change over to hot or heat...only blew out cold air! Anyone have this happen and how did you fix?

 

There is a plug under dash over tranny hump right side,Three or four wire.Unplug and replug,bet you are good to go.