Some forum members have asked about fixing the heater control panel and the cables that are attached. I can say that I was totally freaked out to have to tackle this job. I had almost no defrost and heat for a while and my concern was that the core was done and all the controls fubared. It turned out that the setup is not that bad to understand and trace.
The best way to start is to know that you need to take off some covers and be able to open up the center control panel so you can track the problems. Removal of the center panel is NOT really needed unless there is something totally broken up there. The more important issue are the cables and the clips that hold them in position so that they work to move the duct controls.
Okay, this shot is of the diverter conrtol next to the center panel on the passenger side. Note the blue and black cables? The blue controls the fresh air/ recirc duct. Really it just controls the amount of outside air let in and doesn't have a recirculation option for the E21. See the zip ties on that one? That is because the clip broke and I had no way to fix it. It turned out to be the best way to fix the problem. See the black cable? That one controls the Upper/lower/center panel duct. I chose to epoxy the clip back on (and the darn thing broke a week later. Zip ties for that one, too!).
These two cables are accessible from the passenger side of the center hump. Drop the glove box and release the holding strap to get at the upper screw that holds on the cover over these ducts. Honestly, I've left off the cover as just about no one notices it's missing.
Good luck with your repairs. Here are a few more detailed shots. This one of the zip tie fix on the blue cable.
A close up shot of that lower duct with the cable. Often, the coiled end comes off the selector when the clip breaks.
