My '90 100 refuses to blow heat through the dash vents. It only seems to go to the defrost and floor vents. The volume and temperature also seem low. On cool/AC the dash vents seem to operate normally. I haven't tested the temp on A/C but it doesn't seem cold enough.

That is what my 5ktq does too. I am assuming it is normal. It does make sense that the defrost and floor vents are working in the "heat" mode only. Where you want the heat to be... cold feet and fogged up windows. I can logically think that the cool air comes out of the dash vents only for a good reason too. To cool you on those HOT summer days. SO I didn't give it any more thought. Could I have been mistaken??

Oh the gods that are Audi... tell us, please =)

-Kris

Sorry I dont ahve anything more useful :-)

mine does the exact same thing too. Don't remember when it did otherwise.
Only, my a/c isnt working, but when its on 'econ' or a/c mode, and i push the cooler button anywhere below (I guess) 70.. the vents progressivly get stronger. Same with the rear vents too.

I have never known this car to do otherwise, but, my old '87 5000 sent heat through the dash and plenty of it. I understand that defrost is the default position if anything fails. The fact that A/C comes through the dash seems to indicate that it is not a vaccuum motor. Even through the defrost, volume seems low. I just got this car and tried the heat on a 75 degree day, it should have driven me out of the car.

something is screwy.. check out the various vacuum lines leading to and from the HVAC. Mine started doing the same thing and I need to figure it out.. will post an update once the cause is known.

-tom

I had the same problem on my 87 5000. There is a vacuum problem in the controller, passenger side footwell. One of the vacumm solenoids isn't working due to oil fumes in one of the vacuum lines, thus fouling up the solenoid, the one that controls those vacuum motors. Let me know if you need more information.