I tried to look this up but I couldn't really find anything that helped. My AC/Heat works wonderful....all except one vent. Right now, being the winter, I will put the heat on up to around 80 to warm up the car but when I drop the temperature anywhere below, even to in the 60s, the ONE vent is still burning hot. Literally almost hot enough to burn your hand. The only way I really found to fix the issue is to put the AC on the lowest and it would eventually cool off. I have no idea what the issue could be, I looked up and some people had somewhat similar issues, I hear that it is the settings in the AC and it also could be a TSB that Audi has? I believe I am still under the CPO warranty so I am hoping they could cover the issue.