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  #1  
Old 06-21-2010, 07:57 PM
clintard's Avatar
Hermitus nomadicus
 
Join Date: Jun 2010
Location: Central Illinois
Posts: 50
Plug vaccum element for center vents?

83 300D

My center vents do not blow any air out of them. Any setting i am on i get air coming out of the defroster.

Is it possible to take the glovebox liner out and plug the vaccum going to the pod for the center vents and remove the door so i can shut those vents off manually or will i have to take the dash out?

Im fairly certain those pods are shot since i cant get air through the center vents. Does this mean they are leaking vaccum? And could that vaccum leak be causing my harsh erratic shifting?

I really wouldnt mind having air always coming out of the center vents because i can just shut them off when i need to. Im hoping i can rig this so i dont have to remove the dash.

I appreciate all the help you guys give me on here. This place is a godsend to a first time MB owner.

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  #2  
Old 06-21-2010, 09:50 PM
Registered User
 
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
Your symptoms of "defrost only" point to another problem. If the pushbutton controller is working at all, you should be getting some change in airflow direction.

First, double check the fuses, there are likely two, one for the pushbutton controller and one for the monovalve.(I am talking W126 but the W123 is likely to be similar). You may need to remove and physically check the fuse as sometimes a crack can give you intermittent fits.

The second most likely is cracked solder joints in the pushbutton controller. The boards are arranged in an "H" pattern and over time the joints develop cracks where they meet. Do a search of "pushbutton controller" and "resolder", look for posts with pics. If you don't feel comfortable doing the resolder, www.gdl-online.com and www.programmainc.com are places that repair the controller.

Just plugging vacuum lines will not help and eventually cause confusion when you want to get the system working correctly. It really is a nice system when you take the time to get it right.
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84 300SD 350K+ miles ( Blue Belle )
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  #3  
Old 06-21-2010, 10:34 PM
Memphis
 
Join Date: Jun 2009
Location: Memphis
Posts: 124
The rubber diaphragms in the actuator pods (the pink plastic things that control the vents) eventually dry rot and fail. You can replace the rubber diaphragms by removing the dash, which I did a year ago, which was a GIANT pain-in-the-a**, or you can say that the center vents don't really matter that much. Some people rig the center vents to just stay in the "open" position all the time. The only time the climate control unit uses them is when the air conditioner is engaged. I don't know why the good folks at MB decided that AC should come out of the center vents, but they did. I don't really care where the cold air comes out, as long as it's cold.

That said, vacuum issues can ruin the whole system, including shifting. I think it would be a good idea to look up some of the vac troubleshooting issues on this forum and work the shifting problem for that angle. You can plug the vac lines going into the cabin (which control the door locks, climate control, and engine shutoff at the ignition) and see if it shifts better.

You'll need a handheld vacuum pump to troubleshoot. They are about 30 bucks at any automotive store.

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