Always a pleasure to read about such creative repairs ,especially if a part is no longer available . excellent photographic backup too!
regards
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Glad I can help you all out!

EEEK! I was feeling pretty good about the repair but now I have constant heat from both left and right side vents. Center vent does seem to be changing between hot and cold OK. Any suggestions? Is this most likely a problem with my duovalve repair or is it more likely that fixing the duovalve unmasked other issues?

Sounds like you either didn't get the electrical connector secured properly or you didn't ensure that the valve poppets were positioned exactly like the ones in the earlier picture.

It's critical that they sit up just like the picture because there's a balance in the distance between open and closed. The balance ensures that the valve can direct water either of two ways. If the balance is disrupted, the valve will be biased towards too cold or too hot.

http://i3.photobucket.com/albums/y71...0Repair/18.jpg

Also, hot air doesn't typically come out of the center vents. Only the sides, defrost and floor.

That makes sense. I think the problem may be that the other end of the poppit things that slide in there... those were broken. I was hoping they would still work with just the short part of the shaft to keep them in place but after taking the valve back out, it looks like they were rolling around in there. I'm going to try the "rivet fix" that I read about on another forum to replace those stems. Unfortunately, the spare valve I had for a normal W210 also had broken poppits. It seems that those parts would have worked had they been intact on my spare valve (just FYI for anyone trying to scavenge parts for a repair).

Thanks so much for the follow up. I'll post again as I work through this to hopefully share any further info for others coming across this in the future.

Quick update - I took the valve apart and did the "rivet fix" for the broken plastic poppits and I also changed around the seals and everything so far seems to be working well. I may have flipped around the seals before when I removed them from the very bottom area of the valve for inspection.

On reassembly, I had to guess and it seemed like the concave portion would be the logical side for the poppits to seal against. But in looking at photos here and in other threads, it seems like the opposite is true and the flatter side was supposed to be facing the poppits.

When the concave portion is facing inwards, that creates a much larger distance for the poppits to travel in order to seal them up. So if you are embarking on this repair, make sure you pay close attention to all the little details like this when you are on the disassembly portion! I'm not 100% sure that I'm correct on the final position of these washers but so far, so good. I'll try to post again if I encounter further problems with the valve in operation.

VALVE CLICKING When OFF
 

Thanks for Posting a great article. I did all of this and seems great ! However

When I shut my Car off, I hear "Click....Pause "Click"...pause..."Click... I put my thumb on the Duo-valve and besides it being burning Hot, The Valve doesn't stop "Clicking "...It actually I think killed my battery after not driving the car for a week.

I pulled the fuse and it stops, left the car 2 weeks battery is no issue...

*NOTE: I followed your easy directions because the Duo-Valve was making this sound Prior....

Any help would be appreciated :(:confused:

Freakin' duo valve. I'm just glad I can shut off the side vents and still get cold AC out of the center vents in the front and back!

I have two spares that need work. This is moving up on my list fairly quickly!

Thanks for the write up. I'm sure I will use it.

Jim

Why no parts?
 

It just doesn't seem right that there would be no rebuild kit for the duo valves. After all this time there should at least be an aftermarket kit available, yet I can't find one anywhere. Thank you for this ingenious fix, you should start making a kit yourself and corner the market.....

duo valve seems to be overheating
 

Hi guys,

Does anyone know what's the normal temp of the duo valve? I can barely touch mine on my clk 320. is it overheating or is it normal? thanks

KarTek, thanks for this fantastic writeup. I wish I had found it sooner, I already had bought a replacement valve. I wonder why your seals were in such bad shape... contaminated coolant, or non-MB coolant used in the past?

My main problem was the opposite of yours. I had heated air in summer with the temp set to max cool. Here is a short-term workaround to get your AC working again, for other folks who have the same issue:

1) Start the engine
2) Turn HVAC temp controls both to "Low"
3) Leave engine running, pop the hood
4) Whack the duovalve solenoids with a screwdriver handle or similar item

If the car was hot before doing this, it may take a few minutes for the air vent temps to drop. But for the past couple of months, it has worked to get cold AC. You have to leave the temp on Low and modulate airflow via fan speed, if you turn up the temp at all you may start to get warm air and have to whack the duovalve again to get it closed. If your AC isn't working, you will at least get ambient-temp, non-heated air.

Although my Band-Aid fix described above had been working to keep cold air blowing this summer, I was tired of having to pop the hood and whack the duovalve EVERY time I started the car. So I finally replaced it with a new one, and now the system works normally for blowing cool air. I'll have to wait for winter to see if the other problem is fixed. In summer I'd get heat all the time, but in the winter that did not happen... I'd only get heat when the temp was set on "HI", turning the temp one notch down to 86°F would deliver cold air. Which makes NO sense to me. I already swapped out the control unit with no change. If the new duovalve fixed the winter problem too, I'll be ecstatic.

I took my old duovalve apart for inspection, and found the primary metal solenoid shafts were slightly sticky, and there was residue on the top part that goes into the solenoid coils. Further disassembly revealed the rubber gasket at the upper junction (to the metal plate) was literally coming apart and the rubber bits were floating around inside the center/plastic part of the valve. And, there was a mysterious round piece of metal stuck behind one of the upper seats/seals. The lower plastic plungers/poppets were OK, and the rubber seals/seats were also OK. I was not confident the valve would be repairable, so I went ahead with installing the new one ($$$!).

Click here for more photos of the duovalve disassembled. Sample below.

http://www.w124performance.com/image...uovalve_01.jpg

UPDATE: The winter temperature control problem has been fixed with the new duovalve. I'd be ecstatic if there wasn't a new problem, described here... I now have proper temperature regulation, but there is a vacuum issue which prevents airflow to the footwell area in sub-freezing temps.

:cry3:

If you're speaking of the W210, I had that issue very early in my ownership of the car. It ended up simply being the control rod popped off the flap just inside the foot well heater exit.

I just took the grill off it and reached in with a finger and popped it back into place. Toasty feet!

Can't see the photos!!!!

That's because Photobucket likely kidnapped the photos and held them for ransom, and the original poster didn't want to pay. This went down in 2017 and broke images on forums everywhere. See link below. It's also possible the original posted removed/deleted his images, or account...

https://finance.yahoo.com/news/big-lesson-learned-photobuckets-ransom-images-debacle-191026772.html

This is why it's best to upload photos to the forums, that way the images won't vanish (unless the forum shuts down).

:boat: