I have had time to cool off, so now I will write with 1,000% less profanity. My heater decides to work when it wants to, but never on a 1.5 hour road trip. I tried every configuration of the buttons and temp control, but no heat. The blower works, but blows cold air. Exactly 1 block from my house, I decide to turn the heater on (for the 100th time) and it decides to blow HOT. If I leave all of the switches alone and drive to work tomorrow, it will be cold again. Most likely, it is not the CCU or the silver temp control box behind the glove box (I changed it a few days ago.)

I know I can disconnect the wires to the monovalve, so I will try this next. If you have any more insight as to what it may be, I may not crash my car into a wall!!

Recap: Sometimes I get heat and most of the time I do not. When it's hot, it's HOT.

'83 300D

Thanks!!

I've got a similar problem with the '87. The vehicle produces full heat all the time. So, I change the CCU and replace the monovalve diaphragm (looked OK) and it seems to operate correctly for about 15 miles or so.

Then, without warning, it decides to go to full heat. Shut it down and restarted it and it's working fine again.

Two bad CCU's..........unlikely.

So, I'm thinking a monovalve that's intermittent...........we'll see.........I don't drive it much so I'm not overly concerned with it.

Unplugging the monovalve should provide some insight into your situation with no heat..........

It's all a test to see whether you are truly worthy of a Teutonic machine. A Nietzschean engineer, working on the principle that whatever doesn't kill you makes you stronger, realized that the incredible mechanical engineering and reliability in the rest of the car would likely turn its owner into a Southern European or British wimp unworthy of the epitomy of Aryan culture, so programmed in a repetitive failure of the heating system to test our mettle.

__________________
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

Monovalve Problems
http://www.peachparts.com/shopforum/tech-help/138522-monovalve-problems.html#post1026761

Fixing that Damn Climate Control!
http://rverway.net/~boostd/Climate/


ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
ANOTHER bad Heater!! Climate Control:
Climate Control:

Don't forget the cabin temp sensor too. There is also a temp sensor that senses the duct temp in the vicinity of the area behind the pushbutton unit. I have seen these things go bad and cause all kinds of weird issues.

__________________
Jim

kerry edwards,

That was the most entertaining thing I have read in quite a while. If I told you my last name, you would wonder if the car was worthy of transporting me (my last name is more German than Daimler.)


Anyhow, I just returned from my garage to notice a tear in the diaphragm of the mono valve. I would like to clarify: Can the plastic mono valves be repaired? I was under the impression that only the metal ones can.

You guys rock!

Dude! That's so damm funny I think I'm going to show it to my girlfreind tonight

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

I didn't know there was a plastic vs. metal monovalve. Wouldn't the insert be replaceable in either case?

__________________
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

Here is the DIY you need.

#1. Pull the wire.
#2. Remove the four screws.
#3. Remove the cover/coil.
#4. Remove the plunger (noting how the washers/shims come out).
#5. Install the new plunger with washers/shims.
#6. Install the cover/coil.
#7. Install the four screws.
#8. Install the power wire.

Here is the part you need.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1983 Mercedes Benz 300D Turbo
Part: Mono Valve Repair Kit
Note: Heater Valve
Electromagnetic heater valve.
R3023-15174 Mono Valve Repair Kit Bosch IN STOCK $63.65
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1YE1FF2PQ1YO02O9S1&year=1983&make=MB&model=300-DT-001&category=R&part=Mono+Valve+Repair+Kit

I ordered a monovalve repair kit. The nice part is that the warehouse is located in Ohio, so I should receive it the very next day. I appreciate everyone's assistance in this matter. Gone are the days of the $30 monovalve repair kit! Either way, I'll pay to have heat; the winter has just started.