W639 Vito Cooling fan constant running

Discussion in 'Electronics' started by mike-bennett, Apr 22, 2014.

  1. mike-bennett

    mike-bennett New Member

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    Hi Folks

    I have a Vito W639 and the drivers side electric cooling fan runs all the time, i have checked all the wiring and the relay and it all seems to be fine, i took out the SAM and checked for both internal damage and water ingress and this looks fine.

    Am i correct in my assumption that these fans are only for the air con? i couldnt find a wiring diagram that shows them and as the engine has a viscous fan i could see any other need for them.

    The only reference i could see that may explain extra fans was to a 100 degree switch, im not sure where on the engine this is located or if this may be the cause of my issue, Previous owner has had the vehicle code read, no codes but the specialist suggested its probably the SAM, seemed like a stab in the dark to me as everything else works just fine.

    Any help appreciated.

    Mike
     
  2. BIG UN

    BIG UN Hardcore MB Enthusiast

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    Do you mean the 2 fans at the front of the van? If you take the front grille off you will see them, they are the cooling fans for the AC. Is it definitely those? The easiest way is to get it on star as that will tell you exactly where the fault is.
     
  3. OP
    OP
    mike-bennett

    mike-bennett New Member

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    Yes that's the one, it's all controlled by a relay by the fuse box, I removed everything and tested it. I can't find a wiring diagram for the AC to confirm if the fans are controlled by the SAM but there are no faults on the star and the specialist was guessing its the SAM
     
  4. BIG UN

    BIG UN Hardcore MB Enthusiast

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    You won't find one because they're not, the only thing that's in & around the SAM is the 60amp mega fuse! There is no trigger switch as such it is controlled from the AC controls on the dash which won't allow anything to work if there is a fault.. pressure switches are a common fault on the AC
     
  5. zenman63

    zenman63 Hardcore MB Enthusiast

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    The air con is stand alone and has power to the control unit on the dash from the fuse box.
    Its all controlled from the dash switch and canbus
    The fans have a mega fuse at the rear of the control box, big red fuse.
    I would look at the relay first behind the head light, or the fan it's self.
     
  6. Dec

    Dec Hardcore MB Enthusiast

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    Is this the relay you referred to above, see here… Mercedes Benz Viano Vito 2008 Cooling Fan Relay A0025424419 | eBay

    Dec
     
  7. zenman63

    zenman63 Hardcore MB Enthusiast

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    Yes but cheaper new at MB
     
  8. OP
    OP
    mike-bennett

    mike-bennett New Member

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    Hi

    yes i spoke to MB yesterday the relay was £25 and the harness and relay £146 which seemed a bit steep, interesting that the system is solely controlled from the dash.

    Ive traced all the wiring back to the relay and tested it, unfortunately its a sealed unit that cant be opened, i found that one on ebay for £26 so i will order an MB one

    I was pretty sure it wasn't the SAM before i started as nothing else has been a problem.
     
    Last edited: Apr 23, 2014

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