Just bought a 1991 300E I have a few Questions
 

Hi everyone, I just bought a 1991 300E and am very impressed and happy so far. The car is black with black leather, 159,000 miles, and all service records going back to day one. It was a one owner car. Anyway, here is my question:
The defroster vents on top of the dash are always open, even when the climate control system is off. The faster I drive the more fresh air comes in through those vents. Do you think the actuator needs to be replaced, or is this a normal thing in this car? If the actuator has to be replaced, how hard is it to get at, and how do you do it?
Aside from this small problem, the car is great!

Most probably, not normal, default when actuator is leaking is for it to stay open.

It is labor intensive to replace, dash must come off.

See link: Actuator in photo that circled is the one for the defrost vent.


http://www.peachparts.com/shopforum/attachments/tech-help/35232d1155165524-no-air-center-evapdone-003.jpg

Thanks for the reply, i read somewhere that you can get to the defrost actuator from behind the glovebox? I guess that was misinformation.

I might be mistaken. Maybe the defrost is the one acessible when the glovebox or airbag unit is removed. That top element may be for the center vent.

Hopefully someone else will know for sure.

Edited:

See diagram below. If diverter flap element, one I circled in picture in the link above, is leaking I think all air will go to defrost and not to center vent. Still not sure whether changing defrost element will cure your problem. Hopefully someone else will know for sure.

this can be done without removing the dash but you will need small hands and lots of patience.[by the way there are two diaphrams for fresh air one on each side with linkage to join].

Where are the fresh air diaphrams located? Are they easy to get to, or do you have to pull the entire dash? Is there a way to troubleshoot this problem, before ripping the dash apart? Thanks

#42 in diagram. I'm not able to change them without the dash being apart and the evap. case on a workbench.

You can change this defroster actuator by removing the glove box liner. Look on the left and it's right there. I changed mine a few months back and I have pretty big hands.

It's #38 in that diagram in the earlier post.

Or if you'd rather, just remove it and in the spring move the lever by hand to set it to blow out the center vents; in the fall to blow out the defrost vents.

Do a search. There's more info to be found.

Hey Ron, do you have any more photos of removing that evaporator case? Mine is due and I'm kind of dreading it.

Thanks for all of the input, whats strange is this: My defroster works fine, and when I put the AC on the air comes out of the center vents as it should. The only problem is that the defrost vents stay open all of the time, and let fresh air in constantly. I removed the glove box, and that pod is working correctly. I am confused now since everything seems to be working as it should, except the defroster vents are alway open to outside air. Which pod could be causing this?

Search on this forum using my user id and keyword evaporator and you should find some.
Also search forum in link below using my user id ron in charleston and keyword mercedes and you will find some more.
http://www.autoacforum.com/categories.cfm?catid=2

Its been a while since anyone replied to this post! If the vacuum actuator "pod" is moving in and out then it is likely the defroster flap or the linkage between the vacuum actuator and the flap. An easy way to check is to take your glove box out, and disconnect the metal rod that connects the vacuum actuator to a small plastic piece sticking out of the left-side wall (where you would expect the wall of the center vent to be.) Move this piece forward and back and see if there is any change in the amount of air coming out of the defrost vent. If you can shut off all air from the defrost vent your actuator is bad. If you can't, then it is the flap itself which will require a lot more work for replacement.