W124 Heater always hot

AlanF

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1989 W124 Estate, rescused after standing 14 months with a blown engine!
I have a 1989 W124 estate, last week the air coming into the car from the heater is always hot, when i turn the heater control dails down to cold it makes no differance. Is this a duo valve issue, if not any ideas before i start investigating,

Thanks
 

television

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Hello and welcome to the forum
Yes this could well be the duo valve,,you can double check this with a volt meter and the should be near enough 12v on each coil,,this will show the the control unit is working.
 
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AlanF

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1989 W124 Estate, rescused after standing 14 months with a blown engine!
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Thanks for that, i will check it out this weekend and let you know.
 

joe1972

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Yes, I had exactly this fault, those duovalves fail in open position/ hot. I fixed mine, or rather, bought a replacement unit, then used the excellent post in DIY section to fix ...only for that to fail just recently too! (better than the original one which had woodscrews in it, but not quite good enough to last I guess)
Dammit, at the moment I'm driving around with a bypass pipe so i have no heat......but as already suggested, winter is on the way, so another Duovalve (hope one that works and I dont need to bodge) was on the cards, so I bought another S/H unit, but it's the wrong one for my W124! ...an ongoing saga for me
 
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AlanF

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1989 W124 Estate, rescused after standing 14 months with a blown engine!
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Thanks for that Joel, i intend to look at the due valve over the weekend, hopfully using the DIY post i should be able to get things back to normal. I will update you next week.

thanks again,
 

Alex Crow

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alanf, it is worth doing a resistance test of the valves when they are hot. if you find there is no earth to them even with dials at cold then it may just be due to internal shorts, the control stops controlling when the current is too high.
 


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