On my "new" '91 240, I've noticed that the sliding temperature control for the A/C-heater system seems to be "all or nothing". With the compressor on and the slider all the way to the left, it gets very cold (a good thing.) But if I move the slider even a couple of millimeters to the right to try to moderate the temperature, it immediately gets hot, and stays hot for a while after I move it back all the way left, then it's freezing again. Is that just the way this system works, or is there some adjustment that can be made? Didn't see this question in the archives. (There's also a noticeable detent or sense of the slider riding up over something when I move it all the way left.)