Push botton climate control blues - PeachParts Mercedes-Benz Forum

#1 10-17-2003, 02:33 PM

Have the old 300SD and for some time I noticed those foul push buttons all seem to work the air around correctly, and the heat comes on ok, but the fan has been acting up. Thought I had the beginning of a bad fan, but then the fan blower itself all checked out just fine.
Problem kept getting worse and I was working with it last night and noticed when the buttons are held in had the fan will blow, or when the console is tapped a little the fan will come on or will stop blowing.
I have not had the pleasure of pulling that horizontal button assembly out on this car yet, although I bet I will this weekend.
Do you just remove ashtray and radio and then push that assembly out from behind?
Then, as the vacuum controls all seem to function, is there an 12v connection to the assembly that may be loose, and maybe causing all this?
Any comments will be helpfull.

D.Blake · #2 10-17-2003, 04:12 PM

On my 83 SD, you remove the ashtray, junk collector pocket, then Radio. At the top of the radio slot, there are two screws which fasten the bottom part of the wood face. The five switches at the top come out with the wood face, but not too far. Be careful with pulling out the fiber optic lines to those switches. You may have to unplug and pull each switch to get the wood face out of the way enough. The ACC unit will then be exposed (unlike the SDL version it is not attached to the wood). IIRC there are two screws that hold it in place. I also remember a position adjustment system with these screws. They are in slots with nuts on the other side (I think). Be careful not to lose those nuts or you will either be dissembling more of the console or finding replacment nuts! (don't ask me how I know this!) After they are removed, the unit slides forward. Two large electrical connectors in the back. No vacuum connections. I ended up replacing mine as the fan would just shut off at odd times. I got a rebuilt for about $250. Some folks have been able fix with resoldering contacts (see other topics in this area). If it dosen't work, this proceedure might invalidate it as a core return. While your in there check the function of all of your actuators and switch over valves along the right side of the console below the ACC pusbutton unit. Hope this helps.

84300DT · #3 10-17-2003, 04:59 PM

welcome D Blake - where ya been!?

this should be your home with your stable as listed!

#4 10-17-2003, 07:18 PM

Thank you for the outline. I printed it and will use it this weekend as a guide. Might try to get the unit apart and attempt some soldering. I think I know where another unit is (broke like mine) I can lay my hands on, should I need to get a rebuilt unit later.
Welcome to the Forum D. Blake!

D.Blake · #5 10-17-2003, 07:53 PM

Thanks for the welcome. I was on the MBZ.Org email list for several years absorbing the wisdom of Dr. Booth but couldn't keep up with the traffic volume. I have owned MBs for over a decade now and forums like this help keep them practical. As you can see, I have a completely Diesel Fleet. May be parting out the 240D. My attorney is fighting with the other driver's insurance company (Hartford) now (my son was driving but it was not his fault). There first offer was $650 - Hmmm, I don't think so. Good engine, only 80k on a rebuild. Only about 60k on the rebuilt automatic. Collision cruched the front only, but over $10k to fix. I hope I can sometime contribute more to the forum. Many people here are much more knowledgable than me..

#6 10-20-2003, 07:15 PM

I did the job over the weekend on the 81SD pushbutton unit. I did find, after I had the unit out, that those miserable small bolts that hold it in place to not need to come out. Just loosen them and slide out the whole assembly.
I took apart the plastic case and the two printed circuit boards were exposed. Studied them both and I did note a few bad solder joints. Got my temp contolled soldering iron out and resoldered them. Then I took a look at the little electical contacts on the rear of the assembly. They are activated with 12v current and the contacts looked a little cooked. Most of the bad solder connections were under those small assemblies. I used a can of aerisol contact cleaner and a small contact file to clean those up.
Reassembled and reinstalled. So far so good. Before it would only run the fan when the buttons were jiggled. Now the fan runs all the time and at the speeds it is supposed to.
Not a bad job to do. Worst part was getting the assembly out.