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Very confused A/C; chilin', but not grillin'

Ok, so this is a '98 Audi A4 2.8 Quattro w/about 80k mi.

--The Audi went to my mechanic for routine maintenance, oil change, fluid top off, that sort of thing.

--I also requested that he look at the A/C.

It was blowing semi-cool. So, it functioned fine in terms of blowing at good velocity. It just didn’t cool very well. The air was cool, bu not cold, and it would take 15-20min to make the interior temps bearable. (Granted, the outside temps average 91-100 degrees).

--Finally, I had a minor fender-bender on the driver’s side rear corner. The taillight was cracked, the bumper scraped, and the rear quarter-panel directly in front of the taillight, and above the bumper, had a dinner-plate-sized dent about 1" deep.

I asked my mechanic to do some very basic body work. Just to replace the taillight (which I provided), and to push out and buff the dent.

-->Here’s the problem:

When I dropped the car off, the A/C was blowing normally (albeit a bit warmly), through the vents on the dashboard.

When I picked it up, it was blowing cold, but…it would only blow either through the defog vents by the windshield, or through the floor vents for the heater (or both).

But, it absolutely refused to blow through the dash vents.

My mechanic tried to figure this out for several hours. We finally had to agree that he had no idea why this was going on.

Any thoughts? Ideas? Suggestions?


If you turn the AC off and just put it on “vent”, do you get fresh air from the dashboard vents? Is that air approximately the same temp as the outside air or is it warmer?

(Caveat: on my Ford Fusion, “vent” air is often warmer than outside air because the ductwork seems to be near the engine, which heats the ductwork especially if I park in the hot sun or if I park for 20 minutes after a long drive and then come back to the car. But eventually after driving for a while, the vent air cools down to the outside air temp.)

Many cars today control those vents with vacuum. Someone may have knocked a vacuum hose off when working on it and now it needs to be replaced.

Well, the mechanic can handle making it blow cold.

It’s the other thing…

No, nothing. No air at all out of the front dash vents, not on any of the settings. Blows like crazy from the top and bottom, though.

And the thing is, it started abruptly…just since these repairs/maintenance.

A loss of vacuum was considered.

Especially as there was body work done on that rear driver’s quarter panel…maybe a line was knocked free?

But, my mechanic had no idea where to even begin looking…even after consulting on-line manuals.

There is a little door in the ductwork that controls whether the air goes to the dash vents, the floor or the windshield vents. That door is broken. It seems to work partly, since you can switch from floor to windshield but not dash. The door either has an electric motor or a vacuum motor, I don’t know which but the service manual should say.

The reason I asked about the A/C temp is that one reason the A/C is not cold could be low refrigerant, but another reason could be that the blend door is not working and you are always mixing some heated air from the heater core with the cooled air. (Is the A/C colder when you first start the car and then warm up when the coolant warms up?) The blend door and motor could be in the same unit as the diverter door and motor and it could be an indication of a common problem.

I would try getting the door and motor assembly from a junkyard and replace it.

Thanks!! I figured it had to be some sort of control “module.”

Any pointers as to where this door and motor may be located? Or how I can better describe it?

I have a great supplier for used Audi parts, but I will need to tell them exactly what I need.

Also, I’d like to diplomatically guide my mechanic to the proper solution!

So, my mechanic was not certain where/what this was.

That is, he knew, in general, what I was talking about. But stated that even in his on-line manuals it was not clear as to where this part is located, and what it is, exactly.

Any ideas?