Mono Valve Repair Kit, what is your story?

Don't deny it, I know you have a LOVE/HATE relation with the mono valve.

Who has the best mono valve DIY, and/or pictures?

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ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
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Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

My story... the SD was missing the monovalve and aux water pump when I purchased it. The heat was ALWAYS on. Once installed both, I could then control the climate within the vehicle.

I do not feel like spending $25 or whatever for the new monovalve guts, so I go used. I've found three new ones out of the countless bad ones.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Its so easy to do you don't really need a pictorial FYI....it takes longer to get the spare tire out of the trunk..........but then..much of this stuff comes to me as second nature......

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I was surprised how easy it was to replace the monovalve. On the "Easy to Difficult Scale", I'd give it a ".5" It quickly becomes a "2" if you drop one or more of the screws in the abyss.

Have fun doing it. There are very few repairs that are this simple that can make such a difference in your car.

Keith

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1983 300SD "Helga"

Thank you Billybob

This is From TxBill's old site

http://mbdieseldiy.tripod.com/monovalve.htm

That is a fantastic mono valve DIY.

I used a magnetic phillips screwdriver. Mono-valve repair had to be the easiest fix on my car. I wish the rest would have been that easy.

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1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

I find these S-Class pretty easy to wrench on.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I pulled one out of an '85 500SEL at the bone yard and dropped it into my 300SD. Now I have AC just in time for winter. Seriously though, it will be nice to get cool fresh air in the cabin without having to wear out my window motors every day.

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'81 300SD

not to hijack but I just pulled two really nice ones from the yard. I only need one for the SD. The other is up for grabs. Pm me

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

If I didn't have two spares, I'd be tempted to replace a broken mono valve with a standard manual ball valve. Open it in the winter. Close it in the summer. Sometimes, just sometimes, Mercedes over engineers a solution.

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Cheers!
Scott McPhee

1987 300D

FYI...

I only recently figured out my diaphragm was torn in my TD, so I robbed one from my SD. This could explain... despite replacing almost all of the a/c AND charging with R12 my TD would not get real cold. I only assumed the mono valve was good to go. Might be worth a look.

And the easy rating isn't even on the scale IMHO. Headlight bulb is more difficult to get to.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Wouldn't work. The monovalve opens and closes many times per second. It is not a simple on/off device but a regulating valve that determines if 1 gallon a minute of hot water flows through the heater core or if 10 gallons a minute flow. Without it and using a static valve the temperature of the air coming out of the vents would be at a constant temperature.

I think if you live in a climate with extremes, say Chicago for example, then you wouldn't mind going with cold air only in summer and warm in winter. Using the defrost however might get tricky.

When driving these old cars I think about what types of settings cause the least amount of stress on the various systems. I've heard that the temp wheel can get worn out if you go from max hot to max cold frequently and that you should set it at a moderate temp and leave it there. At the moderate temp it seems like you'd wear out the monovalve sooner. The monovalve is probably cheaper to replace though, right?

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'81 300SD