124 Radiator fan relay (Diavia)

Discussion in 'Electronics' started by philiggy, Sep 13, 2008.

  1. philiggy

    philiggy Hardcore MB Enthusiast

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    Anyone know were I'll get an electric fan relay for a Diavia Aircon system, I assume it must be faulty as I've traced the wiring all round the car and can only find one fuse, next to the relay on the N/S inner wing, which is fine:confused:


    Phil
     
  2. grober

    grober MB Club Veteran

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    The Air handler fan motors are known to fail on these? there will also be several fuses/relay/s inside the main fuse box beside the brake servo unit.
     
    Last edited: Sep 13, 2008
  3. nick mercedes

    nick mercedes MB Club Veteran

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    http://www.readerair.co.uk/parts.html
     
  4. OP
    OP
    philiggy

    philiggy Hardcore MB Enthusiast

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    I've looked, other than 1 relay and fuse on the inner wing theres nothing else, not in the fuse/relay box, under the dash or any where.

    I've just put 12v across each of the fans and they both work fine.

    phil
     
    Last edited: Sep 13, 2008
  5. Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    How are you cheating the system to make the fans come on during your tests? are you testing low speed, or high speed function?

    I *think* there are 2 possible ways, by mimicking high engine temperature, or, by mimicking high refrigerant pressure.

    Edit: forgot to say, if you want to compare voltages / currents around the system, I can take some measurements on mine - I don't have a wiring diagram.
     
  6. OP
    OP
    philiggy

    philiggy Hardcore MB Enthusiast

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    Hi Number Cruncher,
    My electrical know how is very basic, I knew the fans didn't come on with the aircon, so to see if the fans worked I took a lead from the battery to the fan motors they worked so I knew they weren't siezed or burnt out.

    The only fuse I can find is okay there is power to dash switches, pump, and sensor, so I'm going to try a new relay in to see if it works.

    thats as far as my understanding goes:eek:

    Phil
     
  7. Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    Hi Phil,

    I don't think my fans come on straight away, even if the aircon is on, but, after a short while the fans do come on. The fans on mine come on far too soon for it o be engine temperature, so, I'm fairly sure it must be by monitoring the air conditioning refrigerant pressure.

    It's entirely possible that your fan control system is OK, but that there's a fault elsewhere.

    I wouldn't rush to throw parts at it without checking. The relay itself should be easy to check - typically you would connect a battery across the winding, and check the relay closes.

    See

    http://faculty.ccp.edu/faculty/dreed/AT121/at121files/relays.htm

    for more.
     
  8. Dieselman

    Dieselman Banned

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    Invest in a cheap (£5) multimeter and use the voltage test.

    The main pole of the relay should be fed with 12v and the coil with Gnd and an active 12V when required.
    This causes the relay to close so 12V is fed to the fans.
     
  9. OP
    OP
    philiggy

    philiggy Hardcore MB Enthusiast

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    Thanks for that, I'll give it a go

    Phil
     
  10. OP
    OP
    philiggy

    philiggy Hardcore MB Enthusiast

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    I've got one I'll dig it out and try

    Phil
     
  11. grober

    grober MB Club Veteran

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    Sorry if I confused people I was talking the air circulation fan inside the car, not the cooling fans in front of the radiator.:eek:
     

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