I have the dash out... - PeachParts Mercedes-Benz Forum

sublettm · #1 03-07-2003, 08:20 PM

Well I set out this afernoon to replace the diaphragm that controls the center vents. I took the whole dash apart and pulled the old diaphragm out and replaced it. I turned the car on to test out the new one before I put it all back together. It did not fix the problem. I started tracing the vacuum lines and I now have a question. There are two lines that go into a Tee that connect to the diaphragm. One of the lines feeds to another diaphragm on the left hand side of the center console, the other line goes to some little round thing right behind the control panel for the AC. There are five of these little round things and they are all fed by a manifold which has a green vacuum line feeding it. What are those little round things and where could my problem be since the diaphragm isn't the culprit. A speedy response would be greatly appreciated since this is the wife's car and she would like it to be whole again really soon.

Thanks,
Mike

sixto · #2 03-07-2003, 08:46 PM

The diaphragm things are the ACC actuators.

Check that you're getting a decent vacuum reading at the line that feeds the bank of vacuum switches then check that each of the actuators will hold a vacuum -- check at the actuator where you can then check at the bank of switches. Where there's a T fitting, don't forget to plug the third branch when testing.

If all that checks out, you have to know which actuators respond to which ACC settings. It's only in DEF mode that none of the actuators see vacuum. Even in O/off mode with the engine running the defrost actuator should be getting vacuum (so to speak).

I'm far from an authority on 123 AC systems but I think they all kind of work the same way in the 80s.

Sixto
91 300SE
87 300SDL
83 300SD

sublettm · #3 03-07-2003, 09:11 PM

The actuators all seem to check out good. What is the likelyhood that one of the vacuum switches has gone bad? I have never seen this part in a catalog...are they expensive? Thanks for the reply.

Mike

fz500sel · #4 03-07-2003, 09:18 PM

go to **************.com

They have a W123 vacuum system troubleshooting guide for only $20. It explains how to go about troubleshooting the whole vacuum system even down the the transmission shifting being vacuum controlled. Well worth the investment I feel. Great for DIY'ers.