Hello all,

In my recently purchased '83 300SD, I find that all modes of the climate control system cause air to come out of only the windshield vents. It appears if the system is stuck on DEFROST. It actually blows 95% of the air out of the windshield vents and 5% out of the side dash vents towards the side front windows.

Any thoughts on what's going on? The pushbutton panel seems to do the right thing (OFF works fine, EC and NORMAL work with the compressor on and off as they should.) The only problem is that all of the air comes out of the blasted windshield vents!

Is there a stuck vacuum servo someplace? My guess is that a vacuum servo is not moving a door someplace when I change modes. Could this be a faulty pushbutton panel? I know those are known for going flaky. Is this what happens when they go nuts?

Thanks for any and all help!
Neal


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Neal Bhatt - bhatt@ic.net
'83 300SD 190k

Common problem; due to either lack of vacuum or big leaks. The system defaults to defrost so any vacuum leak causes this problem. It is usually the vacuum servos either for the defrost ducts, center vents, or recirculate door. All three of these servos have vacuum on them when max air is commanded. Leaks in any of them causes the default position.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician