More Monovalve - Page 4 - PeachParts Mercedes-Benz Forum

whunter · #46 03-12-2012, 05:51 PM

If you have a spare electro magnet coil, install it.

It is rare, but does happen.

.

Rob Pruijt · #47 03-12-2012, 07:18 PM

If you pull the plug of the monovalve it should stay open.
That way you can see if the problem is electrical or mechanical.

Rob

cho · #48 03-20-2012, 11:04 AM

hi guys

I will use this topic to ask a q. about monovalve, as mine on 84 300sd has melted
I can not use repair kit,.....over here is hard to find proper one, so I wonder
is there any difference considering monovalves on w126 cars (especialy A/C and non A/C models) as mine has A/C.

... or can I use monovalve from w124 or w140 with A/C..?

thanks a bunch

.

WhipperSnapper · #49 03-20-2012, 11:14 AM

Sometimes its difficult to get all the air out of the cooling system on these cars. You might have to temporarily remove the vent hose from the reservoir tank to the radiator or vent it at the thermostat.

Whip

whunter · #50 03-20-2012, 02:59 PM

Quote:

Originally Posted by cho

hi guys

I will use this topic to ask a q. about monovalve, as mine on 84 300sd has melted
I can not use repair kit,.....over here is hard to find proper one, so I wonder
is there any difference considering monovalves on w126 cars (especialy A/C and non A/C models) as mine has A/C.

... or can I use monovalve from w124 or w140 with A/C..?

thanks a bunch

.

You need a W126 assembly to fit the available space, and for the windshield heater port..

.

cho · #51 04-08-2012, 04:39 AM

.

hi,

somehow I manage to find another (used) monovalve as mine has melted
now after install, the things are the same,it is always in open position.

I m suspicious about magnet coil so I would like to measure it,..does
anyone knows which is the ohm resistance on the coil poles?

tx

.

Yak · #52 04-08-2012, 02:45 PM

Factory Service Manual (FSM) shows 15 ohms as the coil impedance.

If your monovalve is not closing, you should carefully measure the electric connections and check the fuses. The hot pin should always have +12v (probably from fuse 14) when the engine is in RUN or START. The ground pin will only be grounded when the push button unit temp wheel is in MIN or when the controller calls for it to close. The monovalve works on a "switched ground."

I recommend caution when probing the connections because you can short the controller and burn the PBU/temp wheel trace.

cho · #53 04-08-2012, 03:00 PM

Quote:

Originally Posted by Yak

Factory Service Manual (FSM) shows 15 ohms as the coil impedance.

thanks Yak,

to be on safe side I pull mine out and no impedance is shown so I guess
this one also is toasted, will give ti to the guys to re-wire ...if possible.

in the meantime I will go with some hot/cold mechanical voodoo

.

strelnik · #54 04-08-2012, 04:42 PM

Quote:

Originally Posted by AUDIBLE

300SDL

Wrestling with no heat at highway speeds. Just installed new monovalve. Did the test suggested by the venerable ah-kay, to wit:

1. Unplug the connector to the monovalve. This will cause the plunger to retract and call for heat ALL the time.
My result: heat all the time, until highway speeds. As speed increases, temp decreases to no heat.

2. Then put a constant 12v on the monovalve such that the plunger will be fully extended to block the coolant and there will be NO heat.
My result: no heat ever.

I also tested the new monovalve before installing it and it operated perfectly. BTW, cooling system is flushed and clean with proper fluid.

So if the monovalve is 100% open as in test 1, is something keeping the coolant from getting to the heater core at high speeds? Is the only reason that there is heat at idle and low speeds because of the aux pump? Is it possible that the valve(not the cartridge part that gets rebuilt) at the bottom of the monovalve chassis is blocking the flow at higher speeds?

Thanks for looking.

I need to read through and really understand the whole 126 climate control heat/ac set-up. Replaced the monovalve on the recommendation of the mechanic who was too busy to diagnose and shot from the hip. Still in the same position. Don't know how to diagnose the AC system so I'm working kind of blind right now.

As I continue to convalesce from my second and last cardio stent, I'll start looking at what I have to do.

A simple diagram of how this stuff works would be sooooo nice on a 126 300SDL.

Scottr · #55 09-19-2012, 12:29 PM

Wondering if anyone has a conclusion on this topic?
I have found myself at the same point, no heat at highway speeds.
Flushed system, de-oiled, citric acid, many water flushes, did heat exchanger flush seperatly after system flush. All compoiants check out good, ie: mono valve not damaged (new cartrage ) aux. pump works well, flushed each part individualy also. Heat is incredibly good ( very important for a car in Fairbanks Alaska) Un plugged MV, same results, plugged MV back in, unplugged Aux water pump, BINGO, heat at idle and highway speeds, Temp wheel controles heat and fan in auto nicely.
Sooooo.... anyone have insight to this. The check valve at the bottom of the valve body is still a mistery to me, but it seems that flow should pull the CV down into the open position. This sure seems to point to weak spring pressure of the MV cartrage, allowing flow to pull it closed? In my case the added suction of the Aux water pump might be enough to pull it closed ?
Any thoughts on this? This has been sorta fun to troubleshoot, sure do thank all of you "seasoned Pros" on this sight for all your wisdome

Scottr · #56 09-19-2012, 02:25 PM

Pulled it last night, perfect condition. head scratcher!!

Scottr · #57 09-19-2012, 03:51 PM

Hmmmm, I understood the system to be spring loaded into the Open posistion and the negative side of the plug was switched, when switched, ( 12V applied) it closes the valve (no flow )

Scottr · #58 09-19-2012, 07:34 PM

Good to hear, I was starting to run through everything again.

Still hope someone can help to resolve this issue.