My 98’ ML320’s temperature control didn’t function properly for more than a year and got worse. The knob turns OK, but air is stuck either at hot or cold. Only way to switch between hot and cold is by turning the knobs back and forth and getting lucky. I went to a shop and replaced a control unit last week.
Now I face different symptoms. The good part is that turning knob from max cold to max hot or the other way around, air temperature isn’t stuck any more. The bad news is that when I turn from max cold towards 2/3 between max cold and middle, all of sudden air becomes hot big time, not even suppressible by AC on. The only way getting back to normal temperature air is turning all the way to the max heat and turning back to the same location. Another observation is if turning the knob VERY slow from the max cold, one click at a time and wait, towards the same location, air will become warm but not hot.
Any suggestions what causes the problem and what is the needed repair?