My heater only blows though the defrost vent 300SD 82
 

so i have my dashboard ripped apart and i have hurd that theirs something that will make this problem go away maby a worn out vacuum control I need to figure out this soon cuz im driving around wihth my instument cluster ducktaped to my steering wheel :D help anyone ive searched the forums but cant find anything when the ac is on although it blows thought the right vents it i dont know this things problem any help would be excelent@

Behind the glove box you can spot three if you look hard... those are always the culprits. One of the three is the defroster one, it's a bit of a PITA to replace without yanking the center panel wood, but do it once and it's simple Of course test the others.

I dont know what they retail for, probably $40-60/ea now.

You might search the threads for the word actuator; should find a good bit of info there.

I stuck a metal brace in floor flap to stay open.Warm now.

I've done this too, seems the wrist pin or whatever it's called, is a weak point on the drivers side floor flap.
Not sure if you have any other issues.

cool ill look i have the whole dash off the car still and i was also wondering why the vents for the rear only blow cold air when the heater is on and when i turn the heater on and the ac at the same time i get heat out of the defrost and very cold air out of the rear vents any ideas?

How do you turn both the heat and A/C on?
IIUC, the center rear vents only blow vent air.

it was the ac that was blowing because the air coming out was sooo cold icy cold. is the rear vent just for ac no heat at all because the last 300sd i had only did cold air through the rear vents

are there any pictures of what i need to replace 0r any DIYs? cuz i want my crap to work right :P it would be very swell!

Correct. The reat vent never blows heated air. The heat travelling back there comes through the floor ducts under the seats (and of course diffuse air from the front).

I have never tracked down my heat problem. I have replaced monovalves, checked pods/flaps with a vacuum gauge and everything should work. But on my SD I only get decent heat in defrost mode. If I select any of the other buttons I get heat on the floor but cold air out the other vents (including defrost). So I finally gave up and select BOTH defrost and an arrow button simulataneously when I need heat. This gives me full heat out of all of the vents and no cold air (or some cold air mixing but hard to detect).

Let us know if you find anything definitive as to your heat problem as my symptoms are very similar to yours and I could never track it down.

yep stupid thing pisses me off why can it just use servos and electronics like normal cars why a complex vaccume system that can get all messed up. I just want to find out why it most of the time only blows from the defrost in heater mode but in ac mode it works perfectly even the tempature wheel works right and it switches and off..

^^German engineers trying to impress other German engineers.
You may have a failing CCU.