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Discussion Starter #1
After some intermittent issues with my passenger side vents blowing only hot air, my research led me to check out the duovalve. I pulled it apart and cleaned it up a bit, and it seemed to fix the problem for about a day or so, but now it's coming back. I know it isn't an electrical issue because I tested the voltage on the power cable and it seems fine. So my conclusion is that the valve itself is failing - either one of the pistons is sticking, or one of the coils is failing.

Now, I'm prepared to replace the valve, but figured I'd hop on here first and see if anyone else has any experience buying one of these. I've found them through a couple of online suppliers for around $230 or so, made by OES Genuine. Is there anyplace that might stock them a bit cheaper or refurbished, or is there another manufacturer of these? The two places I found it are autopartswarehouse.com and partsgeek.com. Any experiences with either of them? Finally, do you agree with my conclusion that the valve needs to be replaced, or is there something else I might be missing?
 

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Are you sure that your r134a level is correct? On some Mercedes, different temperature levels can be a sign of low refrigerant level. It could also be the duovalve, but I wouldn't throw parts at the problem until you are positive that's the issue.

Len
 
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Good advice from Sokoloff..

I have used partsgeek many times, with good success. However, I did recently get front axle seals for the S55 AMG sedan from them (they have the speed sensor 'fan' built in.) Though they said they'd fit my car, and looked good/correct, our AMG couldn't read them.. I had to disassemble the calipers/rotors etc. a second time to replace with oem, which of course did fix it. No word yet on a refund..
 

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don't give up on the DuoValve yet...

It took me 2 tries to fix the same problem. I ended up doing the same thing, pulled the metal pistons, wiped them clean and put them back in. It worked for a week then no luck.

then I pulled them out again and used steelwool to make them nice and shiny, that was a month ago and so far so good!

I suggest you pull it apart again one more time (it's like 2 bolts that takes 5 minutes tops!) and make them nice and shiny! much better than a couple hundred bucks on a that part.
 

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Discussion Starter #5
Thanks for the advice. I'll have to check the refigerant level when I get a chance, but I'm pretty confident that it's the duovalve, considering that it started working perfectly as soon as I cleaned and reassembled it.

Klonny: good point, it's probably worth making another attempt at cleaning it again, especially that it will be easy to pull apart now that I know how to do it. I did hit it with the steel wool last time but maybe didn't clean it well enough. At least the weather has been nice this week so I have been able to keep the top down and not worry too much about the air vents :D
 

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Discussion Starter #6
So yesterday I was out and about all day, and it started working normally for a bit... and then just as suddenly went back to blowing hot air.

Anyways, I took it apart again today, cleaned it all out again, polished up the pistons, etc. and no luck. I should note that even the first time I pulled it apart, it looked pretty clean. Maybe a little residue of some sort but certainly wasn't gunked up. I'm not sure at this point that it could be anything other than a piston sticking or a solenoid failing. I did notice that on one of the pistons it appears that the outer metal coating has chipped off in a couple places. Very tiny, but it may be enough to make it catch. Probably gonna go ahead and buy the part but I'll give it a little time and see if anyone else has any other input.
 

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Discussion Starter #8
UPDATE:

@curro101, I think you nailed it. I did a continuity test on the metal prongs. Closed loop on the right, open loop on the left. Apparently something wasn't making a connection, or at least only was intermittently.

I went ahead and bought the part new through PartsGeek ($225). I was too wary to buy used. Swapped it out today and took it for a ride and everything seems to be working perfectly. I could tell when I compared side by side that the coils in the old one looked pretty well used.
 

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how long does it take to install duovavle

How long does the duovalve take to install?

My warranty company and the dealer have about a 90 minute discrepancy in labor time which they both want to pass the cost on to me. I think the warranty company is right though. 1.8 hours should be enough to put this on.
 

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Discussion Starter #11
How long does the duovalve take to install?

My warranty company and the dealer have about a 90 minute discrepancy in labor time which they both want to pass the cost on to me. I think the warranty company is right though. 1.8 hours should be enough to put this on.
Even that seems pretty generous. It only took me maybe 15 minutes or so, and I'm far from being a mechanic. Granted, I didn't replace it entirely; I just disassembled the old one and replaced all of the moving parts (pistons, coils, etc) so that all that was left of the old one was the plastic base. I wasn't sure whether I would have needed to drain the coolant before detaching the hoses, and there was a rubber grommet holding it in place that seemed like it would be a pain to get off, but I still can't imagine it would take that much longer.

How long did the dealer bill for?
 

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FYI for any future readers.

If the wires break on the coils inside the duovalve, chances are they can be repaired by soldering them back together. Had I thought of it at the time, I'd have taken pictures.

My duovalve first blew maybe around 2004. Back then I checked it and sure enough, only one side was working. I pulled it apart and I unsoldered the broken coil inside, unspooled one circle worth of wire, repairing the broken/short wire. I snipped and soldered the thing back together. It worked flawlessly until last week when I repeated the performance. This time I also polished the pistons as they were getting a little messy looking.

It works like a champ once more!

I guess i'm only saving around 50-60 dollars as there are tons of em on ebay now.
search "Valve 1147412114 0018307784 ". Back in the day it was several hundred dollars and a kiss on the cheek from mercedes. I decided to just go ahead and fix it again this time since I had done it before. Fortunately once I got a little wire and was able to test, I had the same ohm reading on both coils. (if one is really far off, it could be a sign that the coil is burned up)


Note: this requires soldering very fine wires in very little space. if you're not that good at soldering, i'd suggest finding someone who would do it for you. Also, when soldering/testing the wires, use a lighter to burn the varnish/invisible insulator off of the ends of the wires. when i tested the coil i believe i got around .02 ohms that showed it was good.
 
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