i kind of added this to the end of my last post, but thought i would make a new one just for this problem. i've read posts where people are having trouble getting their ccu buttons UNSTUCK, but i have the opposite issue. i have to fiddle endlessly to get the any of the buttons to hold when i press them. eventually, i can usually get them to stay, but its entirely annoying to fiddle with them, and presumable not great for the system to be turning everything on/off rapid-fire until my buttons stay pressed in. is it possible that each button is somehow dirty, or in need of cleaning, or more likely a vacuum issue, since they all seem to have the same problem?

i have an '82 300sd

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1982 300sd, 230,000 miles, svo/wvo conversion... yellow

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It's definetly not vacuum related. I'd venture a guess that the buttons are dirty or that they mechanism that keeps them depressed is dirty or broken. Pull you CCU out and look at the buttons and mechanism.

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I would guess that one of the button mechanisms is actually stuck down, even though all the buttons themselves look like their "up." The stuck mechanism would prevent the other buttons from being depressed, as when one mechanism is down, the others "pop up." I'm making things up, because I've never actually cracked into the thing, but I just thought I'd offer a theory based on how the buttons generally behave. I had a problem where one button would stick down so you could not press any of the other buttons down. I took the cc unit out one night with the intention of cleaning the buttons and mechanism, but I discovered it was too dark to really see well, so I put it back in. The buttons have worked perfectly ever since ... I guess by jolting it around upon removal I knocked some dirt particles loose or something.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

can of compressed air can have magical qualities compared to the air we foul from our rear

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commercial fisherman diesel in my blood in my boats trucks and Dear old Dad has had me drivin them since i got my first license in 1968
1986 300 SDL 427654
1999 Chevy Crew Cab Dually 225423
1986 300 SDL 287000 Dad's
1987 190 Turbo 158000 Mom's (my inheritance)