I have the exact same issue. Out of the blue the vent to the right of the driver seat get extremely, almost burning hot. No other vent goes hot, just that one. Nothing seems to be wrong with the AC and how it works according to one mechanic. The dealer told me that there is nothing wrong either, but it could be some "flap" inside that sticks and lets in the heat from the engine/motor. (Sorry, I know zero about cars and the proper terminology.) At the dealer's it would cost over $2K to have it fixed. So for now I just either shut it off and lower the windows or go topless (the car, not me). Sometimes moving the temp dials around works, but not always.

I would love to hear about a fix for this.