Stuck on defrost

I have searched the forum and don't see any posts about the problem I am having. Last night it was very cold -33 celcius and the heater control was set to floor/defrost so I turned it to defrost and it was very hard to turn so I did it slow and it went to defrost. My wife tells me this morning that it will not leave defrost the dial turns but nothing changes any Ideas???

Nevermind the knob is broken lol