My 1999 318i SE heater pumps out (very) hot air even when you select cold temperatures. Any ideas?
(I have put more detail into another question, but foolishly put it all in the title block, Doh)
Assuming that you have correctly adjusted the thermostat and vent settings to moderate the heater temp or to choose cold temp, then the car has a defective IHKR (manual ac) thermostat switch or a defective
IHKA (automatic ac) control module. An extremely rare possibility is for the vent stepper motors to get stuck in the heater position.
The above comments of course considers that the ac itself is in good working condition.
I think your gonna have to take it to a garage and have it looked at. If its something simple they won't charge you much, and if its more complicated you wouldn't be able to fix it anyway, so you have nothing to lose by taking it in.