I have no heat in my car - well maybe a little, but not very much. I believe from reading the threads that my monovalve is to blame, so I am going to dig further and then order up the parts, trouble is, it is cold now, so I was wondering if it is possible to remove the guts of the monovalve and run with full heat and just control the temperature with the fan speed until I get the parts? Is this possible and make sense?
Thanks

First of all, post your car (model and year), as all cars are different. If your monovalve has an electrical conection to it, simply unplug it. This will give you nothing but heat.

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1989 300E 144K

If the monovalve diaphragm is torn, removing the electrical connector will not give you heat.

Additionally, it's not possible to remove the monovalve diaphragm (actually an assembly) and operate the vehicle without it.

It did on mine even though it had a torn diaphragm. Can't really explain why it did.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

That's certainly a strange deal.........wonder if you had more than one problem?

If the diaphragm can lift when voltage is removed, presumably the CCU can accomplish the same thing??

You could remove the entire monovalve and connect the two water hoses with a short length of copper pipe. That would give you heat assuming everything else works in whatever car you have.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

This is what happened with mine. I had a small tear. Once coolant presure was high enough, it would force coolant into the solenoid body and push the plunger down and close the flow to the heater core. If I shut off the car and started it back up, I would have heat, but not for long.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Precisely my symptoms before i disconnected the monovalve. I then had full heat until I replaced the monovalve guts and hooked it back up again.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

My 90 sdl just quit supplying heat.
Air comes out the correct vents.
I can't seem to see a mono valve...hose just enters into first firewall.
HELP!

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

sorry, I edited my signature to show I have a 1982 300sd. I have enough heat at first start up to clear the frost of the windshield, but it is quite cool while driving. It isn't totally cold but not warm like it used to be. It could take a couple weeks to get the parts, so I can't take the monovalve out, but it is cold now (-20) so could I remove the diaphram to get full heat?
Freezing in Saskatchewan
Corey

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1982 300sd
1980 300cd (sold)