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  #1  
Old 10-05-2008, 10:38 AM
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w124 heater - monovalve - how it works

Ok, can somebody tell me how does the heater of the w124 works?
I know that the monovalve is connected directly to the 12V and works with ground inpulses! So, if no ground than you have full heat (valve opened), with ground you have no heat (valve closed)! My question is how do you have worm temps??

Another question, the w201 heater isn't electronicaly operated like the w124, it's vacum operated, it seems like an easier setup, hould it be possible to fit a similar setup in the w124?

Note: forget the AC!!

With kind regards,



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1985 200D (w124) and totaled 190D

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  #2  
Old 10-05-2008, 01:02 PM
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The controller in many Mercedes cars of this vintage uses Pulse-width Control Modulation (PCM) to control how much hot coolant is allowed to enter the heater core. That is, the electronic circuit pulses the coil in the monovalve so that the valve is open for a small amount of time and then closed. The ratio between the "open" time and the "closed" time determines how much hot coolant gets into the heater core and thus how warm the air is that blows out of the climate control vents.

One of these days, I need to put an oscilloscope on the monovalve and measure the frequency of the pulsations. Can't be more than a few Hertz since the monovalve has considerable inertia.

Jeremy
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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."
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  #3  
Old 10-05-2008, 01:15 PM
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All this questions because my cc fried, and I canīt find replacement ic's for the unit, 23 years old ic's!!!
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  #4  
Old 10-05-2008, 01:20 PM
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I would guess fractions of a Hertz.

You can use any kind of valve to regulate the flow of coolant to the heater core. The question is how you control it. What you have at this point is a PWM signal. How do you use that to control a vacuum operated regulator? The simplest thing would be to adapt a cable operated heater valve from something like a 1970s vintage car, or something like this - http://www.danhard.com/sub2.htm (lower half of page).

I'm curious to know what problem you're attempting to solve. On cars with US version ACC, the monovalve is rarely the problem. It's usually a ground problem, worn blower motor blowing fuses or a bad ACC control unit. I'm not familiar with MB manual AC systems of this vintage but I imagine it's a combination of manual controls and an electronic temp control unit similar to what's used in 123 and 126 ACC through 1985.

Sixto
87 300D
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  #5  
Old 10-05-2008, 01:32 PM
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Looks like you posted before me

You might look into adapting a US 123 temp control unit to your car. You can probably find one for less than the postage to mail it to you.

Sixto
87 300D
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  #6  
Old 10-05-2008, 02:53 PM
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My problem is that I have always heat coming how the vents!
My w124 doesn't have A/C, I disassembled the control unit and found several burnt diodes and resistors, I swapped them all but after closer examination I found a bit missing from one of the IC's! I donīt want to buy a refurbished one or one from the scrapyard, I donīt know how long it would last!

I also disassembled the monovalve, inside it the rubber that seals it has a tinny hole but I know there are kits for it's repair!

As for the auxiliary water pump I know that with age, it starts consuming a lot of current and that could be the cause of my burnt controler board.

For now the water pump is disconected and the controler board is in my bed table! I have the monovalve conected directly to the battery so I don't have heat inside, the cold weather is now starting and soon I'll disconect it for heat, I'm thinking of rigging an on-off button to do that from the dash!
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  #7  
Old 10-05-2008, 03:23 PM
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What I had in mind specifically is something like this -

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=350104228587

And something like this -

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=390000535605

Calling it primitive is being kind but it's more sensible than full on and full off.

Sixto
87 300D
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  #8  
Old 10-05-2008, 05:42 PM
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W124 ACC design

Quote:
Originally Posted by mouramen View Post
. . . As for the auxiliary water pump I know that with age, it starts consuming a lot of current and that could be the cause of my burnt controler board. . .
The W124 cars' ACC is designed with a circuit that senses over-current in any of the controlled elements (including the aux water pump) and shuts down (a) the entire controller or (b) just the affected circuit – depending on which revision of the ACC you have. I suppose that the protection circuit could fail or any one of a dozen other reasons.

A junkyard controller might at least be less damaged – maybe not damaged at all. Worth a try and inexpensive, at least compared to a new or rebuilt one.

Jeremy
__________________

"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
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  #9  
Old 10-05-2008, 06:35 PM
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Quote:
Originally Posted by sixto View Post
What I had in mind specifically is something like this -

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=350104228587

And something like this -

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=390000535605

Calling it primitive is being kind but it's more sensible than full on and full off.

Sixto
87 300D
LOL, that's a realy good idea, a good and inexpensive solution!

I've got a vaccum operated heater valve from my totaled w201, is it possible to connect it to the vaccum system of my w124?
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  #10  
Old 10-05-2008, 06:54 PM
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This might help with control - http://www.geocities.com/chmwatson/FAQs/mbc.html

Or you can connect it to the headlight level thumbwheel if the factory look is more important

Sixto
87 300D
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  #11  
Old 10-06-2008, 03:22 PM
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Quote:
Originally Posted by sixto View Post
This might help with control - http://www.geocities.com/chmwatson/FAQs/mbc.html

Or you can connect it to the headlight level thumbwheel if the factory look is more important

Sixto
87 300D
Thatīs more like it!!
I've got one of those to, from my late w201!
What vaccum line could I use?
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  #12  
Old 10-06-2008, 09:26 PM
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If you have headlight adjustment, you already have the vacuum line in place. Just route the line from the headlights to the vacuum controller. Otherwise, if you have ACC, there is a vacuum line from the engine compartment to the selector manifold beside the radio. Manual controls use cables AFAIK so the only vacuum in the dash is for engine shutoff. The brown tube is supply vacuum, the brown tube with red stripe goes to the shutoff actuator.

Sixto
87 300D
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  #13  
Old 10-07-2008, 05:46 AM
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I don't have ACC!

Can I use the line that goes to the headlight adjuster and not loose the headlight adjustment function?
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  #14  
Old 10-07-2008, 07:07 AM
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On the older versions of the mono valve, and I suspect yours as well, there is a diaphram that does rupture. I repair kit is avail for them, runs about 20.00. You may wanna give that a try before anything else? Good luck.
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  #15  
Old 10-07-2008, 10:54 AM
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Quote:
Originally Posted by dieselnutnj View Post
On the older versions of the mono valve, and I suspect yours as well, there is a diaphram that does rupture. I repair kit is avail for them, runs about 20.00. You may wanna give that a try before anything else? Good luck.
I can do that...but...I still have the fried control unit board!!

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