I did a search for the vents on this forum and too many replies too many suggestions. I am confused. Please can some one help me. I am not too keen on removing the dash board.

OK this is my problem on 1985 300D turbo, 4 door sedan 123, 179,000 miles:
When I press the defrost button all air comes out thru the defrost vent on top of the dash board. Seems like this is normal.
then
when I press anyother button, things work fine- I mean the flaps for the center and bottom vents close and open properly I checked it with a flash etc. but the defrost air vent on the top of the dash always is on and send air thru it. As a result my center vent throws air at much lower velocity. and there is a lot of moisture condensation on the outside on the windshield due to the cooling caused by inside air from the defrost vents.
Does the defrost vent always stay on( I drove the car for 2 years thinking this was normal- how silly of me.)

Any quick suggestion seems like a very typical problem with a pinpoint solution. I thought may be someone had an exactly same problem and found a fix for it PLEASE HELP
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Hi Bill: Thanks for the reply
The airflow thru defrost vent is slightly higher than ( or may be almost equal to) the air flow from the central vent.
So where do i start. What sequence of checks or repairs I have to do?
Do you know the location of the air contol unit that may be causing this problem?
I am new at AC controls.
Thanks
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Well I got my the MB ACC manual. I am trying to read it few pages at a time( Boy I did not study this hard even during my pharmacist exams).
Its all making a little sense so lets see how things go. I still have to get the vacuum tester.

By the way can someone tell me how come MB, famous for its durability, designed such a break prone ACC system. I think they were drunk when they designed this stupid ACC.
Sorry I had to let my frustration out.
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Larry Bible sent me a great diagnostic bulletin for ACC. Either post or send me a private message with your fax number and I'll be glad to fax it over. This bulletin never leaves my office, due to the number of times I have faxed it.

The hope is, the more I fax it, the more time that Larry has to provide his excellent advice.

Let me know,

JCD