I've been repairing the climate control on my '82 300TDT and I found that the only vacuum element that had failed was the dual-acting defroster element. The only places I could find it, it was listed as "Special Order, Limited Availability". It also cost about $100. With a desire to get the car back on the road sooner than later I took a gamble and ordered the MUCH more readily available and significantly less expensive ($40) dual acting element from a W124, part #1248001175. It looked remarkably similar. I figured I might have to bend or swap the arm and possibly rig the mounting. It turned out to be even easier than I thought. Apparently the guys at Behr like playing with legos. Yes, the arms are different, and yes, the mounting is different, but it all clips together just ducky. I had to drill out the rivet on that held the old arm in place.


After that, I un-clipped the arm from the new part. It comes with a nifty little clip and the hole size and offset are perfect for the w123 arm. I un-clipped the base and un-clipped the top part (the nipple comes out the side on the new one and is in the center of the old one. It all clipped back together again perfectly. Maybe 10 minutes, start to finish. Here it is all reassembled.

And here it is reinstalled.


BTW, if anyone needs to install just that element, it is fairly easily accomplished by removing the lower panel and instrument cluster and detaching the left vent tube and moving it out of the way. No dash removal necessary. If vacuum lines from vacuum solenoid valves 1 and 3 leak, then it is very likely that element that is bad (both go to that element).

Nice job.

Nice job. Thats a healthy price difference!

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'82 300SD - Somewhere over 220k - Becoming reliable...

My 2 cents. All of the dual diaphragm valves that I have seen always fail at the bottom diaphragm, this is the one that is easily replaced. These things are a dime a doze at the junkyard. You will have to break the donor apart to pull the top diaphragm but it works just fine in the lower position.

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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

Interesting. My upper diaphragm was the one that failed. I couldn't R+R it without cutting a little connecting metal tube which meant that the whole center assembly needed to be replaced.