On my 85 300 SD my far right button o is stuck in the in position I can push the other buttons in but far right one will not pop out so I have no heat and no fan on any speed to push air. Right before this happened I had smoke coming from center of dash and then smoke stopped. Where do I start looking for problem?

Mercedes w123 Maintenance: Automatic Climate Control Unit Repair

If it looks like this one, then maybe this will help you investigate the problem.

If it was plastic smoke I'd start looking for a replacement.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

I would not ignore this...

http://www.peachparts.com/shopforum/diesel-discussion/241899-i-lost-all-electrical-fire-high-up-dash.html

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both my kids cars went to junkyard in 2023
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1998 E300DT sold to TimFreeh
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Wow great article gatorwesty that gives me a good idea how to get started. I was hoping if I can get the far right button marked o to pop out that I could get some heat again as it is getting a bit chilly again in N.W. In. I will keep an update of my progress with this matter.

I was able to get the button o on far right to come out hoping then my fan would work on any speed but it does not and at this point do not know if I will have any heat in the car. Is there a fuse somewhere that controls fan that might be blown? I looked under hood in fuse box on drivers side and did not see any blown. Im hoping that since I got the climate button o to come out by prying it out that I can operate some of the other doors in heater core to get some warm air in car even w/o fan just thru flow of air. Till I can get to pulling the climate control unit out.I will drive car shortly to see if there is any heat coming out.

A while back on a trip I had smoke come out of my climate control area then stop. When I pulled climate control out it looked very fried. A forum member said he could check it out but instead I bought a whole different used unit stuck it in and everthing works again and I have heat. Problem fixed thanx for respones and suggestions.