Have 1984 300 sd which I recently purchased for $900...Previous owner said a/c went buggy and her father "rigged" it so at least she would have heat.

I know that if the monovalve is bad, it will default to all heat all the time. But I live in Austin Texas and DON'T NEED THE HEAT!!!

Need to take a small 200 mile round trip tomorrow with the wife and kids who will complain about having the sunroof open and the windows all the way down.

Any way to disable the heat?

Thank You,
Sweating in Austin

Have never owned the 126, but if it was me I'd start with the fuse box and pull the fuses that are HVAC related. However, one fuse you might want to keep intact is the blower fan.....Next, I'd seek out the monovalve (located on firewall of engine compartment?) and manually shut off the hot water supply from the engine. Using bailing wire and duct tape, as necessary, you oughta be able to close the hot water valve.

Easy.
Leave the wife and kids at home.

__________________
Dave
1995 C280
1999 Triumph Daytona 955I - my speed fix.
1982 300TD - Gone, but not forgotten.

If you are careful you can squeeze the rubber hose leading to the heater shut with a vise grip. Simple..cheap..temporary.

__________________
Dana Linscott
Vegoil converted truck...vegoil converted 1987 190DT, 300 series next.

http://vegoilconversions.netfirms.com/

no flow = no heat or little heat

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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
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Thank you all for your replys...leaving the wife and kids would cost me nookie from the bride and care and feeding in my old age from the yardapes...

Standing on the passenger side...looking down into space next to battery, I see square silver plate with 4 screws, a small cylindrical shaped dohicky on top, and an electrical plug. I assume this is the top of the monovalve assembly. Below the top, two hoses connect into the bottom of this assembly: one on the inside closest to the passenger compartment, the other on the outside closest to the engine.

Which one do I clamp?

The car runs exceptionally well and I would hate to do anything that might cause her to break down or overheat whilst in the hinterlands with the family. Sweating would be preferable to roadside meltdown...

The silver plate with the four screws is the mono valve. What would happen if you unplugged it? Does anyone know if that would stop the heat?

Tom
'82 SD
'86 SDL

Assuming its got the same hotwater flow as the 123..... passenger side is intake to the heater box. Driver's side that goes to the cylinder head is the return line. So you probably want to clamp the engine passenger side hose - and pack it with rag under visegrip teeth.

You can clamp either of the two lines, and the flow of hot water will stop.

Geez, vice grips hanging on a coolant hose for a 200 mile trip sounds pretty scary to me. If you're going to go that route, why not go to the auto parts store and get some hose clamp pliers? They're not expensive, and can come in handy some times.

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Found this article which gives great instructions and pics for replacement.

http://hvac.articles.mbz.org/plumbing/monovalve/

WHUNTER was kind enough to send this reply in response to my query:

<<< If this is not enough, clamp either heater hose.
Worst case, buy a chunk of heater hose, unhook both heater hoses from block and make a loop block to block, useing the hose you bought.
Good luck.
Sorry we could not talk, work has me slammed, at the moment.
whunter>>>>

I cannot for the life of me figure out where the "the small cylinder in line before the square mono valve" is. From this pic, can anyone point me in the right direction?

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Hello txballstryker
Trace the heater hoses from the bulk head; to the engine block.
You will find the Auxiliary Water Pump; here is a picture of the unit.

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If you look at the picture,where the arrow is
there should be a hose that runs to the front
of the engine.
Follow this hose and you'll see on the
chassis the aux water pump.

Louis.

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Thank you to everyone...esp WHUNTER who went above and beyond in returning my call from Michigan in the middle of a workday...God Bless