I got my jeep 2 years ago and want to keep everything working properly. The middle console dial that changes the fan direction(window defrost, center, and feet) is not changing when prompted. my mechanic mentioned something something to the tune of a diaphragm that was broken when he replaced my heater coil. he was not able to get a replacement part at the time and put it to defrost as a default setting for safety reasons. does anyone know what the part is so i can actively seek one out and replace it? I tried searching on a part site but could not narrow it down

 

Are you asking about what vents the air blows out from? If so, you have a vacuum leak. Those doors are vacuum operated. A common issue is a break in a vacuum line under the battery or damage to the vacuum reservoir behind the front bumper on the passenger side. Loos of vacuum causes the vent to default to defrost. It's certainly possible one of the lines to the servo or to the back of the vent control broke.

 

I thought the problem with the reservoir you're describing was the older generation of XJ. I didn't this was a concern on the 97+.

You can YouTube several videos that show you what vacuum hoses to look for on the 97+ models. Just search Jeep XJ stuck on defrost.