I am the original owner of a '91 90 with nearly 350k miles. I rarely drive it anymore because of the heating and cooling situation.
I cannot get a/c cold air out the vents that I want as most of it comes out of defrost or heater ducts. And in the winter, I cannot get hot air from any vent at all. The temp cannot be changed at all. It's either cold or cold. I have replaced the ventilation control to no avail.
Also, as with most Audis of age, the foam lining in the ducts has blown out. So could that mean the mixer doors are jammed?
And I read somewhere once that a vacuum pump controls the mixer door functions and I question the health of mine. Perhaps a weak vacuum pump would explain why my braking system isn't as strong as it once was. Any info on the vacuum system would be greatly appreciated also.
And one last tidbit of info. I can smell coolant inside the car while while driving. It is enough to steam up the windows in the winter but the carpet has never been wet from a leaky heater core. I do know for a fact the water pump seal is leaking and wonder if the smell and moister is coming in through the air intake at the windshield. Any thoughts would be greatly appreciated.