PeachParts Mercedes-Benz Forum - View Single Post

rhodes2010 · #2 03-29-2010, 12:44 PM

I have the 1980 with same setup. 300D, but I think it should be the same.

A couple ground rules:
1. Defog will always kick in as it is wired electrically and acts like an override
to all other settings. We can always get defog to work.
2. All other buttons - bi-level, auto-hi, auto-lo are vacuum switches
controlling vacuum on or off.

There is one vacuum line running from the engine bay through the firewall
to the climate control switch system. This line can cause the problem if
not providing proper vacuum. This line is on the drivers side and can be traced
and checked.

We have to check each thing one at a time and move forward.

Our cars also have a bundle of vacuum lines running from the Auto Temp II
AC Servo to the cabin on the passenger side through the firewall behind
the battery. This bundle generally is okay but individual lines can go bad and I
have replaced a few.

Check that enough vacuum is getting to the center console panel.
Drop the panel under steering column and find the one line that goes
to the climate control button panel, my line is green I think.

A year ago something under the hood was causing vacuum loss (low vacuum)
and this caused the climate control panel to get low vacuum.
I found the problem under hood and moved the climate control line closer to the pump so vacuum would be closer to the source.
That took away the issue for that particular problem.

I am sure others can give more insight on this issue.