i had a broken diaphragm and exchanged the monovalve. Now the heat works but I can't turn it down with the dial in the dash... heat is always on!
What is wrong here?
The dial electronics were replaced about 8 years ago..... is the problem the new monovalve or is it the el. board?

Martin

The mono valve needs voltage applied to shut and stop the flow. It is designed to be fail safe to the open position.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The same thing happened to me. The new monovalve was no good.

Did you remember to plug the monovalve back in after you put in the new one?

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

Thanks...oh my...did I forget to plug it in? I don't think so but you never know.
I'll dig it up again and double check...

If it was plugged in (which I assume for now) ...the new unit might be bad.
It was probably a cheap Uro [junk] part.
Maybe better go with OEM?

Best, Martin

Unfortunately there is no "cheap part" for this application. Get it from the dealer and never look back.

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Jim

Put a 12V across the terminal of the mono-valve. Polarity does not matter. If you still have heat then the mono-valve is bad or you did not seat it properly. If no heat then it is the CCU electronics.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I found the problem. The wires were not clipped on properly. Maybe the clip is bad... but it works now. Thanks for all your help.

Best, Martin

Same thing with mine...the plug wasn't making a good connection. Took it apart, tightened the connectors by squeezing with a pliers gently and all is well.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I had the same problem in the middle of LA summer nonetheless - oof! I just replaced it about a month or so ago. So disappointed with the quality / precision of the replacement Valves I could find - ended up having to buy a second one because the first wouldn't fit. Second one was super tight as well but managed to file it down to get it seated properly.

after a couple weeks of heating now my monovalve quit again: no heat. I assume the URO part is dead (why not banning URO)
Does someone have the MBpart number for the repair diaphragm?

Bummer: I saw that my Aux pump is missing.... I guess it was replaced by a copper ellbow. What part number is that pump?