Climate control knob stuck

Went to turn on my ac and the climate control knob was very tight and felt stuck. I was worried it would not go back and it didn’t. Something has it stuck. Took the cover off to check it out. Couldn’t do much to see the problem. I’m thinking something has the flap door stuck. Any ideas or ideas to jimmy rig it so my heater will work? Thanks

 

Well I was able to jimmy rig it a bit and undo one of the cables and push the lever over so the heater would work. Checked out on YouTube how to do the heater core and it looks like a nightmare to do. You have to take the whole dash apart. Cluster out and everything.