w123 Leg Room Flap Vacuum Question - PeachParts Mercedes-Benz Forum

will_t · #1 02-18-2015, 12:30 PM

First, the door locks an engine shut-off on my 84 sedan are 100%, and the car holds vacuum for days. The vacuum operated leg room flap element checks out - it holds vacuum and operates the flap when i pull vacuum on it with my hand pump. But the line from "the system" that pulls the actuator is pulling very very little. I put my tongue on the open line with the engine running and could feel faint vacuum pressure, but very faint. Can anyone tells me where I might go from there to try to get this thing sorted out?

Thanks,

SD Blue · #2 02-18-2015, 12:56 PM

According to the FSM vacuum diagram, it may be something awry with the check valve that feeds the manifold for all of the switch-over valves or possibly a restriction of some kind.

Here are a few links that might help you sort it out:
http://www.peachparts.com/shopforum/general-information/248948-mercedes-service-manual-source-cd-dvd-paper.html
Mercedes-Benz Model 123 - Disc 2
http://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Climate/83-604a.pdf

will_t · #3 02-18-2015, 02:34 PM

[QUOTE=SD Blue;3443594]According to the FSM vacuum diagram, it may be something awry with the check valve that feeds the manifold for all of the switch-over valves or possibly a restriction of some kind.

thank you. i'll have a look at the links. in the meantime, is the checkvalve on the engine side of the firewall?

thanks again

SD Blue · #4 02-18-2015, 05:38 PM

I'm thinking it is just due to where it is in the diagram. However, I don't own a W123 so I can't say for sure. Maybe someone here on the forum will chime in and point you to where is is for sure.

MBeige · #5 02-18-2015, 07:30 PM

The switchover valves have electrical input, control given by the PBU, if memory serves. Legroom actuator is #39 in diagram below, with one vacuum line (red/yellow).

TnBob · #6 02-18-2015, 08:52 PM

ANY vacuum issue = time to get a Mityvac. Our favorite auction site has them all the time.
or... waste hours and hours chasing an issue Mityvac would solve in mere minutes.

will_t · #7 02-18-2015, 11:01 PM

ok, well i have a hand vacuum pump with a gauge which is also sold as a tool for bleeding brakes so i'm not sure i need to go out and get a mityvac, but thank you for the suggestion just the same. the check valve is indeed on the engine side of the firewall, but in my sedan, for whatever reason the green vacuum line that comes from the switch-over valve manifold is connected directly to the vacuum source (a four-way) instead of connecting to one leg of the check valve. my check valve connects to the vacuum source (the four-way) and one leg is connected to a yellow with a red stripe which disappears above the steering column (and i couldn't tell where from there even with the instrument cluster out) and the other leg to a solid yellow which i think must go to the vacuum reservoir, because it disappears up into the car body above the instrument cluster and below the windshield. anyway, the green from the switchover valve manifold is connected directly to the source so i presume the manifold is getting good vacuum pressure. (what i don't know about that is if it is bad that it's not on the check valve). the check valve itself seems to be working (by the mouth test anyway). the leg room vacuum element, however, is still not getting vacuum pressure. the element is indeed fed by an orange line (as in the diagram), and although i can't see it all the way to the switch-over valve, i'm pretty sure it is connected to the second one from the left - well, i'm hoping it is. so could the culprit be a faulty switch-over valve? or could the line itself be no good? and by the way, note the (44) throttle orifice in the diagram. i took it out of the rubber connector tube section. it seems to restrict about 95% of the flow. but even with it removed there wasn't enough vacuum pressure in that orange line to operate the vacuum element. so in conclusion, two questions: 1, is it "common" to replace switchover valves, like do they go bad, and if so, is it difficult to do? i mean, there's very little room to work in there! and where do you buy them?! and 2, if possible maybe i should snake a replacement plastic line in there and see if that doesn't work, because if it doesn't, wouldn't that point toward a faulty switchover valve?

thanks!

SD Blue · #8 02-19-2015, 10:43 AM

Please put some paragraph breaks,capitals and punctuation in your text. It makes it easier to read and sort things out.

Your comment about the green manifold line being connected directly to the vacuum source makes me wonder. From your description, it sounds like a couple of lines may have been swapped near the 4-way connector and the check valve for the reservior. Sometimes those lines get knocked loose during oil changes and get reconnected incorrectly.

will_t · #9 02-19-2015, 11:13 AM

All:

Please accept my apologies for lazy writing.

I'll put the green line onto the check valve and connect the yellow/red stripe line directly onto the 4-way. I'll leave what I think is the reservoir line (solid yellow) on the other leg of the check valve.

Separately, I will pull the red line from the #14 legroom flap switchover valve and pull vacuum on it to see if perhaps the line itself is no good. As I have mentioned previously, the element itself seems good (holds vacuum and operates the flaps) but doesn't respond when the system requires it to operate the flaps.

If the red line to the element checks out, I suppose I'm left with a possibly faulty switchover valve (perhaps unlikely?) or maybe a bad climate control module. I have another one or two of those laying around so I can swap one of them in and see if that's what's going on.

Thanks for your input and helpful suggestions,

will_t · #10 02-19-2015, 02:56 PM

All:

It turns out the reason my leg room flap vacuum actuator was not getting enough vacuum pressure was that the throttle/orifice in the line just before the actuator was restricting too much flow. My vacuum lines were a little wonky at the check valve as well, so I put them where they belong, and then removed the throttle/orifice, and the legroom flap opens and closes as designed. I will order a new throttle/orifice and install it before I use the system, but at least now I know why it wasn't working.

Thanks to you all, your input and suggestions got me to where I needed to be, and without your guidance I probably would not have been able to sort it out.