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#1
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Mono valve electrical specs
My mono valve only works when I directly connect 12v to one side and ground the other side. Then it works perfectly for the summer. Then I disconnect the wires in the winter.
In order to get it working correctly, what voltage should I be getting at the wires that connect to the mono valve? Are there any write ups that explain this? I suspect that the ACC unit is bad. 1984 300CD US |
#2
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The monovalve is 12V. The ACC switches the ground side, so you more or less have to back probe the connector to test functionality.
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#3
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Does anyone know of any complete writeups on this subject?
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#4
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The ACC consists of multiple "units." Except when OFF, DEFROST, Max Heat or Max Cool is selected, the monovalve ground circuit is switched by the electronic unit for temperature control.
__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl. |
#5
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That is true. The 123 ACCIII system consists of two control units. The pushbutton unit on the dashboard and the regulator unit behind the dash. The pushbutton unit is basically passive and just contains relays and switches. The analog electronics that are responsible for temperature and fan speed regulation are in the box behind the dash.
This control box is often forgotten but is the root of many 123/early 126 issues. When the 124 was introduced, the system was integrated so that everything is in the pushbutton controller unit. The 126 facelift was introduced concurrent with the 124 and they adopted many of these same systems in the 126. First thing I would try is opening up the regulator box and replacing every electrolytic capacitor and inspecting the solder joints on the board.
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The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech |
#6
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There are two regulator units. One for temperature and one for fan speed.
__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl. |
#7
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That is correct. The blower speed decision is made by the regulator and then the command passed to the blower controller. This switches different resistors on the line to change the fan speed.
On the 124/later 126 this was done by a solid state device yielding infinite speed control and greater efficiency.
__________________
The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech |
#8
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Or you could do this change and eliminate your monovalve frustrations:
https://klimakit.com/product/monovalve-and-coolant-circulator-pump-eliminator-upgrade-kit/
__________________
Sam 84 300SD 350K+ miles ( Blue Belle ) |
#9
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That's nice and all, but it doesn't get around the original ELECTRICAL problem. The Monovalve works if he applies 12V. The problem isn't that the monovalve doesn't work, it's that the CCU isn't closing it off.
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