In defrost, What closes the center air outlet?

[dhillman]

In defrost position (default), no vaccum, what closes the center air outlet? I am missing something that closes the center air outlet behind the heater.

Darrel

[Duncan UK 190]

I cant work out the heating controls on my 190 either. I think its like programming a video, I need to find a 6 year old to do it!
(Or perhaps buy a manual from mercedes)

[mbdoc]

What model car?? on the W201 chassis(190) you must close the lever. ON almost all other USA cars since 1983 the climate control system releases vacuun & the vent is closed by spring pressure on the vacuum element.

[dhillman]

I have my blower housing unit exposed right now. The dash was removed. I removed the top cover of the center housing for the heat exchanger or heater. with a mirror I can see that there is no flap or door to close the air delivery from the evaporator to the top cover. That means that the center outlet is always delivering air as long as the blower is on. The only way to close it is manually at the adjusment in the dash itself. I remember that before the air delivery was controlled automatically and that sometimes there was no air delivery through the center outlet. I noticed this after sending the car to an A/C shop for repair. They replace the evaporator, but I am not sure if they modified the housing. At this point there is a perpetual air delivery through the center outlet unless you close it manually. There is no flapper controlled by the vaccum elements that can close this area between the heat exchanger and the evaporator. There is one flapper with a vaccum element that controlled the air delivery after going through the heater then through the center outlet though. But closing it does not stop the air flow through the center outlet. Please reply if you can understand what I'm talking about.

Darrel

[Freestyler]

Originally posted by dhillman
The only way to close it is manually at the adjusment in the dash itself

That's exactly how it works on my '86 300E.

But what i think is worse is, that the center outlet can ONLY deliver cold air..!? -Which i think is very annoying. I would love to hear the MB designers reason for this..

Freestyler

[95300YDT-A]

Dear Darrel,
we still don't know what car you are talking about : W ???.
On my W 124 193 ( a 300 TD turbo) as on most MB's of that
period, the center is allways blowing cold. While warming your car you can keep your head fresand cool!. I like this system.
To shut off you have only to turn the small wheel in the center.
If that don't stop the airflow than check the wire connected to this wheel or lever. On the right side of the wheel you will find a small Allen-screw that should hold this cable in place/connected to the wheel. Is this screw fastened than you should check the cable...
Please let us know your findings.
Good luck,
Danny

[dhillman]

Thank you Danny and sorry for not being specific. My car is a 350SD from 1991, it is a USA edition chasis #126134. I believe the ACC in the USA version might behave different from the European edition. I thought that at one point when my car was in defrost there was barely any air coming out from the center outlet, even with the external door opened. After sending the car for A/C repair (to change the evaporator) it is blowing cold air constantly through the center outlet even in defrost. I thought they might have removed something, but I cannot identify any part, door or flap missing. The heater/evaporator housing is now exposed, and there is no evidence of a missing door. Steve told me that it should be automatically controlled by the ACC, but I need to get to the door that is missing or inactive. The car was bought here in Puerto Rico through the only Authorize MB Dealer in the Island.
If you happen to know some infromation please reply. I am in the process of getting everything back in place, with new vaccum elements.

Thank you again for replying to this thread.

Darrel