How to restore ACC fan and outlet controls?

[Feather535]

When I acquired my 280 SE a couple years ago, the AC compressor and temperature controls weren't working, but the controls for DEF, BI-LEVEL, AUTO-HI and AUTO-LO would change the fan speed and which outlets air blew out of.  After a few tests, I determined that the servo wasn't working, so I removed it and opened it up thinking maybe it could be repaired. The case wasn't cracked, but the motor and gears inside were corroded and seized, so not repairable by me, at least. 

I put the servo back on and reconnected all the electrical and vacuum lines, but opening the thing up was probably a mistake, because now none of the ACC controls except DEF--which I know is the default mode--are working anymore. And now there is a sound of a vacuum leak in the cabin, even though I didn't touch anything in that area.

Is there a practical way to get the controls working again without buying an Unwired Tools unit or an even more expensive aluminum-bodied one? I don't really need AC, but would like to be able to direct air to the windshield, footwell or center vents.

[daantjie]

It might be unrelated to you removing the servo.  Often one tends to think one thing lead to another but this is not always the case.  If you can hear a vacuum leak it must be pretty bad and if indeed related to the ACC then yes nothing but DEF will work.

Might be worthwile to pull the passenger side knee roll and plastic ducting off to see/hear where the leak is coming from.  A very common culprit for leaks is the large vacuum pod which controls the fresh air flap.  If you crawl into the legroom area and look up you'll see it.

[Feather535]

Good point!  The current problem isn't necessarily a result of the last thing I did.  The hissing noise does seem to originate in the area above the passenger footwell; I'll take a look.

[Feather535]

I'm not really certain what I'm looking at here, but there is a split in the diaphragm on the blue pot at the bottom of the picture.  There are also two vacuum hoses that are open and not connected to anything: one is all black, and the other is black with a white stripe.  A third loose hose has a metal plug in it.  I think this is the test hose, and it should be possible to pull a vacuum on it.  I tried that, but no vacuum. Any ideas?  Anyone?

[daantjie]

For starters that pod is toast as I suspected.  Replace that one first and see how she goes.  I think they're still available new from MB.

[Feather535]

Anyone have a part number for that vacuum pod?

[daantjie]

000 800 17 75

I looked at this number, might be NLA, oops.  But...if you look at the R107 one, very similar and might work, I'm sure Benz used the same element on various models.

Part # 000 800 08 75 is for the R107, maybe also W123.  Not 100% but worth a gander methinks.

[Feather535]

Thanks! Apparently it is still available from Mercedes, at least in the US:

 https://classicparts.mbusa.com/oem-parts/mercedes-benz-vacuum-element-8001775

[rumb]

https://mercedessource.com/store/1973-1980-vacuum-door-lock-actuator-diaphragm-repair-kit

Just the diaphragms for blue pods.


https://klimakit.com/product/complete-vacuum-actuator-rebuild-kit-r107-380sl-560sl/

For the red pods.

[daantjie]

Just further as well to the open vacuum lines you saw.  They are supposed to be open vents so just leave them as is.  If you look at the schematic in the service manual you will see that they should be open to atmosphere.  The plugged line is indeed a test port, but for now leave it be and focus on replacing the vacuum pod for the fresh air flap. If you're lucky this will solve the problem and you would have spent a relatively short time in ACC Purgatory