Hello,

I've got an untypical question that I can't find any good information on. I am looking for the purpose/need/replacement/guru knowledge on the vacuum restrictor and check valve element. Specifically the center vacuum pod.

In my research, the manual shows a vacuum restrictor and check valve in line from the defrost upper pod/center vacuum source. These two both tie into one connection for the center vents element.

My car, at least as it was sold to me, does not have a restrictor or check valve.

It looks like the climate control restrictors are red bands that squish over the squishy vacuum hose and reduce flow that way. The inline ones for the engine are inline, of course.

I have a few red bands sprinkled amongst the other elements that appear to have restrictors according to the manual. So all signs point to me needing some. However, the general working process doesn't quite make sense to me. Both a check valve and restrictor in parallel suggest to me that leaks are inevitable and complete checking of the vacuum isn't possible. Maybe it's supposed to allow the flap to ease close as opposed to slam shut which could cause a noise complaint?

I appreciate any ideas!

Let me be clear up front that I know nothing about your particular system. On many applications the check valve and restrictor in parallel are supposed to limit a sudden loss of vacuum on the system. When vacuum is applied to the actuator it is applied through the restrictor so that the pump can keep up. When the vacuum is vented it vents freely through the check valve. This may be how your system is designed, but again, I don't really know.

I'd like to see an image of these, I seem to have missed it in my various factory shop manuals .

The foam padding / sealing decayed and fell off on my 240D's fresh air flap so now it makes a noticeable 'thump' whenever it changes over .

If you have a Mity-Vac tool and can't get the system to hold vacuum, there's a leak, it sometimes takes a while to locate it, don't rush you'll be well pleased when it all works .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

http://www.peachparts.com/shopforum/attachments/diesel-discussion/51569d1201071505-vacuum-diagrams-1985-300sd-acc-vacuum-diagram_88tyf648.gif

Having difficulties posting my own image from either device I have. Laptop is currently dead unfortunately. If the above link works, it is someone’s photo of their interpretation of the manual. It shows the check and restrictor I am referring to. And yes, this isn’t an image of the correct 5 pod setup I am referring to. Trying to find an accurate image.
It looks like I may have a restrictor for the central flap. It is on the inlet vacuum side to the solenoid though.

As far as leaks are concerned, I’m getting all that squared away. I had my central flap repaired or so I thought. My defrost pod was bad, so I jumpered its two vacuum lines together. The central pod therefore had two sources of high vacuum flow. When I replaced the defrost pod, the “oem” routing proved to be insufficient vacuum. The flap needed a booster to allow it to hold. This was due to a leaky pod that could still pretend to do a good job. But, while I wait for that pod to have repair parts come, I wanted to see the reasoning behind the parallel piping arrangement.

https://www.benzworld.org/cdn-cgi/image/format=auto,onerror=redirect,width=1920,height=1920,fit=scale-down/http://www.benzworld.org/forums/attachments/w123-e-ce-d-cd-td/151108d1196083754-acc-vent-vacuum-control-vacuum-color-diagram.jpg

More accurate image. Still not the exact diagram I’m referring to from the old startek files, but it conveys the message the same.


Seems like the idea is when the center flap is asked to open (solenoid opens and supplies a good vacuum source) it opens quite quickly using both the check valve path and the restrictor path. When the element would be asked to close, the check valve would fail shut and all the flow have to go to the solenoid vent via the restrictor path. So it closes slowly… open fast close slow is all I can figure. Restrictors on the fresh air and foot flaps just give it a one speed open and close mechanism. All I can think is that the center flap would thud if it closed too fast…

Thank you for those .

I see #44 are the restrictors and #45 is the check valve .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

From what my sleuthing of my own car tells me, the foot flap and fresh air flap have external red bands (270 degrees of a full circle) that squish the flexible line.

In an ac evap replacement picture, the yellow check valve is clearly shown. Can’t quite discern if the restrictor is an external type or in line. I would guess in line since a 4 way rubber and 3 way rubber could be used to connect everything. I wouldn’t imagine a brand new type of connector being used.

It’s definitely interesting. The vacuum source for my center flap does a wierd loop type deal where it is stuffed into the cavity of the evap box. On this loop is a red restrictor.

I’m definitely making things way more complicated than necessary, but I’m curious as to the why now.

I don't think you're making it more complicated, the Engineers made it and once you understand how it works you can maintain it better .

I used to have a chart of the various restrictors size and matching colors with part numbers, IIRC there were five different .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better