I'm sure this issue is listed in here somewhere but I had no luck finding it. When in heating mode (automatic or low) my system keeps the set temperature by alternating from max heat to freezing air. Very little moderation. No issues with fan speed. I changed the dash sensor, bought a refurbished CCU (for a different issue). Might it be the climate control computer? Or maybe the dash sensor broke. I bought it in the summer from Performance Products and it worked fine with the AC. The wire tip sensor part does not look like the original. Quite annoying to be hit with cold air through the center vents once the cabin has warmed up. After it "cools down" heat comes out of the footwell vents and the process repeats. I don't remember my '85 300D doing this. 1984 300D.