Duo Valve w126, 300se Mercedes

spacemoc

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Where is located Duo Valve in w126 300se 1988 ? Can not locate it, please help
 
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television

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number 5 should be near on the firewall back of engine

m.mycat
 
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thank you, will try to locate, but picture is always the best. So if someone got photo of that part please provide.
 
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Heating Problem

what is the difference between Duo Valve Switch and Air Circulation Switch ?? My car only heating warm once stopped engine and started again, then is okay.?? Which part I have to swap ?
 

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Duo Valve switches the hot air ON if dial is turned to Red - OR - switch the hot air OFF if the dial is turned to Blue.
Air Circulation Switch controls the speed of the blower motor fan, example… http://www.google.com/search?q=A/C+....,cf.osb&fp=b96af787733acd64&biw=1200&bih=670

Does the blower fan blow fast and slow?
Not clear what you mean by “only heating warm” and “then is okay” after starting?

Dec
 
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spacemoc

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Duo Valve

sorry my mistake, I will explain now: once started engine and put dial to red there is medium warm air, I have to stop turn off the car start it again then hot is properly warm. Yes fan is blowing okay no problems. I think so Duo Valve is opening on the engine ignition but doesn't work once driving and changing dial from blue to red.
 

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If you have a volt meter, you can measure the voltage on the actual duo valve, is the fault the same both sides
 

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Also, try disconnecting the power supply to the duo valves… like in the picture below… and then check if the air will stay hot all the time.

Dec

163106081_3cf23a1c02.jpg
 
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yes it's the same both sides, doesn't matter which dial you use. That is not (on the picture) the duo valve from w126 300se but thank you for advice. will test it
 
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spacemoc

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Test Done on Duo Valve

I have run few tests on the Duo Valve in my w126 Mercedes 300se 1988, results below:

1) once power disconnected from duo valve air temperature is without change, so if was hot it's hot if was cold is cold.

2) It's very difficult to remove that Duo Valve from the car, but very easy to open it, so I did it and pictures are displayed below, I think so I have to change that as it looks rubbish lol, please tell me your opinion.

3) do I have to remove and replace whole thing or I can easy just replace the middle?

4) You can see on the pictures below how rubber is destroyed and tear a part.

1.jpg

2.jpg

3.jpg

4.jpg

5.jpg

6.jpg
 

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When the power supply has been removed from the valves, both valves should be open , allowing hot water to circulate through the heater… did you wait for a long enough time to allow for the engine to get hot so the air could be heated as it went through the heater?

What is the running temperature of the car, does it get up to its normal running temperature… whatever it is supposed to be?

If you clean them up and put them back again the may work ok and if the stay open the will give you heat for the winter and give you time to fix the problem by summer. You need a temporary solution for now I presume.

Don’t know what exactly you would have to replace but you might find something on ebay, example… http://www.ebay.co.uk/itm/Mercedes-...ent-S-Heater-exchange-duo-valve-/150697013593

Dec

Edit, if the 2 rubber seals (in Red) are removed be fore the valves are replaced then you will have/should have hot water going to the heater.

attachment.php
 

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spacemoc

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Engine temperature is perfect 82 Celsius.

Yes I have wait 10 minutes and after unplugging power from duo valve air was hot all the time or cold all the time depending on it's first position.

I don't like temp solutions :) have ordered second hand duo valve and will replace the middle part as I think so the one I have got are used :)
 
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spacemoc

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Have replaced the unit with the spare one and problem still exist. so have to stop and start engine again then all is working with heating. I will try to describe problem again:

- once started car first time, waiting for engine temperature to reach 82
- put dials on hot (red) - air is sort of warm a little
- I have to stop and start engine then air is burning hot as it should be
- then I can change to cold, hot, cold and is working until next time I will start the engine...

Thank you
 

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Must not be the duo valves then, you will have to get the temperature control unit checked out or try a replacement, seems to be an electrical fault, figuring out where that is not going to be easy, I have no suggestions on that score.

Dec
 

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You need to measure on the connector, the center pin is ground, and there should be 0 to 11volts roughly depending on if the controls are set to hot or cold on each outside pin, one of the pins is for one side of the car, and the other for the other side hence duo
 
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spacemoc

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Test Done

I have tested middle of duo valve with 12volts on the car, basically I have removed the middle and connected to system, then I have moved dials hot , cold, hot and cold. both pins are working properly. I mean they open and close when it should be.
 

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Do not forget the circulation pump,,, when the duo valves are working correctly, you can feel the pulse on the outputs, some thing like a heart beat
 


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