My 1982 240D does the same thing and always has, I've had the car 20 years now .

If it's not too cold just open the side window, otherwise turn on the AC to quickly clear the mist off the inside of the glass, as soon as the dash vents begin blowing hot air close the window or turn off the AC.....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better