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Slow speed fan problem - Guide to fixing

Discussion in 'Mk1 Leon Guides (1M) 2000-2006' started by tobrien1, Oct 5, 2011.

  1. tobrien1

    tobrien1 Guest

    Here’s a guide on fixing the notoriously common slow-speed fan fault. It’s cheap and it works.
    I followed the guide to fix the same problem with a Golf but thought I’d write up a guide specifically for the LCR as it’s slightly different.

    Faulty fan symptoms:
    • Coolant temperature goes above 90
    • Fans only cut in intermittently (or 'pulse') on high speed - this is loud enough to be heard inside the car
    • Fans don't come on when aircon is switched on

    Reason:
    The fans have two speeds, low and high. The resistor (which is built into the fan unit itself) for the slow speed burns itself out which causes the fans to 'pulse' and come on at a hotter temperature than they normally would.

    Troubleshooting:
    There's a quick and easy test to see if your fans are working correctly.
    • Start the car with the heating and aircon switched off, open the bonnet, check that the fans are off (they should be at this point).
    • Switch the aircon on (you should hear a little click as the aircon and fans switch on)
    • Check under the bonnet again, if your fans are working correctly you will see one or both of the fans running nice and slowly.
    • If they look like they're running on high speed (quite audible) stand and watch them for a couple of mins. You'll probably notice that they come on fast, then switch off, then 30 secs later they come on fast again, then switch off etc. If this is the case, you have faulty fans!

    The fix:
    As the fan unit is sealed you can't replace the faulty resistor (terrible design flaw) and SEAT suggest that you replace the whole fan unit for approx 400 of your hard earned pounds (and no doubt it will happen again at some point).
    In this guide we effectively bypass the faulty resistor and add our own working ones into the wiring before the fan unit - for a fraction of the cost!

    What I used:
    10A cable – I got 4m but probably only used about a 1.5m
    2x 1Ohm 100w ally clad resistors (Farnell order code 1174282)
    Some heat shrink (Farnell order code 1259196)
    Heatsink compound (Farnell order code 3821511)
    Metal brackets (From Wickes, they were called ‘heavy duty angle brackets’)
    Soldering iron and solder
    8x M3 nuts and bolts
    Electrical tape
    Some cable ties

    The most time consuming part was finding a place to mount the resistors as there’s hardly any room in the Leon’s engine bay. I tried following the guide to do this on the Golf but the Leon has a second intercooler mounted right where the guide tells you to put the resistors.
    So here’s how I did it:
    I started by removing all of the plastic that covers the battery and then taking the battery out.
    Remove the 4 bolts holding the battery tray in and remove that too:
    [​IMG]
    Drop the undertray off then when underneath the car facing forwards you’ll see to the left side of the fans, 2 sets of 3 wires (brown, white/red and black/red) going into a couple of plugs. This is the wiring for the fans that you will need to cut into for the resistors. I’ll come back to this:
    [​IMG]
    [​IMG]
    Next, wire up the resistors with about 30-50cm of cable on each side:
    [​IMG]
    And heat shrink the ends of the resistors to help prevent any moisture/dirt getting onto the connections (I just used a hair-dryer):
    [​IMG]
    Line up the resistors on the metal bracket and drill some holes to match those in the resistors:
    [​IMG]
    Next wire up the resistors (this is the fiddly bit so do one at a time). Choose one of the sets of wires and cut the red/white wire. Wire this into one side of the resistor, doesn’t matter which. Now splice the other side of the resistor into the red/black cable. So one side of the resistor replaced the red/white circuit and the other side joins into the red/black circuit. Electrical tape all of the connections.
    Here’s a wiring diagram kindly borrowed from the Golf guide:
    [​IMG]
    Test that it works by starting the car and turning on the air-con, the fans should come on slow speed.
    Now do the same for the other plug – and test again.
    Next cover the back of the resistors with heatsink compound as this should help to dissipate the heat a bit better from the resistors (they get quite hot if the fan is on slow speed for a while):
    [​IMG]
    And bolt them onto the metal brackets. Then you can mount the brackets so they hang over the side of the battery tray (using the screws for the battery tray to hold them in place). Sorry, this is where the pics get a bit sketchy, it was a bit hard to get my phone in the right place:
    [​IMG]
    [​IMG]
    ^ You can see the battery tray clamping them down.
    Cable tie all of the wiring out of the way so that they don’t risk getting caught by the fans or touching the resistors.
    I decided to mount them where they are, mainly because there’s almost no other room in the engine bay, but also because they sit behind the fans, so when they’re used and get hot, they are cooled by the fans being on.
    Hope this guide helps, it was a bit of a pain to do, but probably cost about £25 to fix rather than £400 that SEAT wanted to replace the fan unit (which would inevitably break again).
     
    #1 tobrien1, Oct 5, 2011
    Last edited by a moderator: Nov 21, 2011
  2. RabReith89

    RabReith89 Active Member

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    Mate this is so much easyer!! Your a legend, can't wait to get started on the weekend :)

    Could I get the resistor from maplins or dose it have to be from above?

    Also this should be made a sticky :)

    Rab
     
  3. Slimy

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    You'll more than likely find Farnell a lot cheaper than Maplin, especially for those big resistors. In fact, I've just done a quick search on Maplin, they only go up to 10 watt.
     
  4. tobrien1

    tobrien1 Guest

    Doesn't have to be from farnell but does need to be 1ohm, 100w :) they are probably one of the cheapest anyway and have the other bits in stock :)
     
  5. cupra r1985

    cupra r1985 Guest

    hello mate, would you do this on my lcr,if you would how much you charge?an where abouts do you live ?
     
  6. IH786

    IH786 Full Member

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    Got mine from RS Components, they are cheaper than Maplins too

    Need to mount mine in a better place they are hanging on the driverside front corner at the moment!
     
  7. Engimaneer

    Engimaneer The Anti-Sheep

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    Nice write up! Great work including places to buy and good pics.
    It would be nice if you could summarise the symptoms of the fault and any tests to prove this is your issue for anyone on here not familiar with this common VAG fault.
     
  8. tobrien1

    tobrien1 Guest

    Thanks for the feedback. Good points, I've added symptoms, the reason why and troubleshooting steps for anyone that needs a bit more info on it :)
     
  9. Indy

    Indy MK1 LC Red Devil :)

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    Hi, guys I'm pretty much sure that my cars got a problem with the fans where they start up for a few seconds, shutdown and then start up, I will definitely give the resistors ago and see if that helps.


    I have a question in regards to the Fans setup, as my cars a stripped out track day car and as I am no longer running an air con unit, do I need to do anything different to the wiring of the fans?
     
  10. tobrien1

    tobrien1 Guest

    I wouldn't have thought so, the only reason aircon is handy is to test that it has worked, as pressing the aircon button turns the fans on :)

    I guess the other way to test it is to get the engine up to temp, give it a good blasting and then leave it idling, eventually it will heat up enough to need the fans to come on.
     
    #10 tobrien1, Jan 9, 2012
    Last edited by a moderator: Jan 9, 2012
  11. dvance

    dvance Active Member

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    This thread over on mkiVs was quite useful when I fixed mine. I used the plate schematics supplied there and ended up fixing the plate up behind the left headlight on the outside of the battery (basically on the subframe).

    http://uk-mkivs.net/forums/p/59897/488123.aspx

    Also includes instructions how to check if your fans aren't working apart from the basic turn aircon on check.
     
  12. SubZero

    SubZero Active Member

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    Couple of questions for people who have done this fix:

    Is the following wire ok?
    http://www.ebay.co.uk/itm/Twin-Core...ecialistRadioEquipment_SM&hash=item43aa408c82

    Am I okay to split the wire into two and use one strand only? If not, what wire do you guys recommend?

    To fix the resistors to the bracket, will M4 bolts work, and what length do I need them to be?

    Is the heatshrink necessary? Won't electrical tape do the same thing?
     
  13. SubZero

    SubZero Active Member

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    Are the Heavy Duty Angle Brackets effective heatsinks? The uk-mkiv threads use aluminium, which is the metal of choice for heat dissipation...

    Could someone please share a link or provide specific details on which wire to use..? Will a 15A wire be better to use than a 10A? Will the thickness/strands etc make a difference?? Anything else I need to take into account? Don't want to cause a fire in the engine bay due to using the wrong materials! :confused:
     
  14. tobrien1

    tobrien1 Guest

    10A will be fine, I guess you could use 15A if you wanted to though.
    The heatsinks, although made of steel did the job for me, where I've mounted mine, hanging over the side of the battery tray gets a decent amount of airflow and the bonus is that when the resistors are being used they are cooled by the fans themselves.
     
  15. SubZero

    SubZero Active Member

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    Good stuff, will be using 10A then.
    Are yours just being held down by the battery tray (and directly facing the fans) or have you bolted them on somehow?
    Also, have you had, or heard of any problems with ESP light coming on as a result of this mod? Some of the early NIME boxes had this problem...
     
  16. Crhome

    Crhome Active Member

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    Only part I don't understand is the wiring part. So there are 3 wires right? Black/Red, White/Red and the Brown cable. If I connect Black/Red and White/Red to 1 of the resistors, what happens to the Brown cable? Brown stays as it is? Also what do I connect to 2nd resistor? Are there 2 sets of different coloured wires to connect for each resistor? I don't know if I have explained myself correct. Shed some light please into my noobness.

    Cheers
     
  17. Kambo

    Kambo Active Member

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    I'm an electrical newbie aswell :blink: and I have to do this on mine so thanks for taking the time to do the write up [B)]

    Back of the fan plug you have one plug with three wires, so brown gets left alone, one end of the resistor wire which you've made up goes to red-white wire which gets cut and the other end of the resistor gets spliced into the red-brown wire, therefore you only have the one bare wire from the red-white wire which was cut earlier so that loose end needs to be taped up right?

    Can someone just confirm that is right before I go to work on mine as it doesn't mention to tape up the red-white wire which was cut, just that one end goes to the resistor

    Also silly question, if the fans don't work is this because of the already burnt factory resistor? so if you hook this up on fans that didn't work before they will now as the fans themselves are ok but the resistors were goosed, anyway to test the fans beforehand?

    Thanks
     
  18. Crhome

    Crhome Active Member

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    There is no red-brown wire. There is red/black, red/white and brown on its own.

    Ok I had a go at this 2day and totally messed it up in the end. I got through some stages easily such as soldering wires to resistors, drilling brackets, heatshrinking ends of resistors but when it came to wiring them up I got totally confused although I thought wiring part was gonna be pretty easy. I used dimensions of the resistors to buy the right size of brackets. So I am very sure that I had the right size brackets. 1 of them lined up fine with battery tray nut holes but other didn't. I managed to secure both resistors in the end but then when it came to wiring it I messed up. There are 4 cables that needs cutting and connecting to resistors, what happens to other 4 cables that is left unused or not connected. Also which ends of the wires do you connect resistors to? The unit that carries wires out of fan frame or the plugs? Since soldering is awkard under the car I decided to use crimping set to connect wires underneath the car which didn't work out well at all. I wanted the connections to be strong and not dodgy. I ended uo connecting 1 of the resistors and started the car to check if I get slow speed spin on 1 of the fans but nothing. Now I have no clue what to do. Can someone who has already done this fix please advise on wiring and how to establish best connections of wires underneath the car??

    Thx
     
  19. Kambo

    Kambo Active Member

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    Sorry I haven't done this but did have a quick look, yeah my bad it was just a typo when I put red-brown, I meant red-black so yeah there's brown, red-white and red-black

    Not sure why your cutting four wires, you are only supposed to be cutting one wire on each plug so two in total, just the red-white wire on each plug, the red-black doesn't get cut just the sleeves get pulled apart so its exposed, so one end of the resistor you join to the now cut red-white and the other end of the resistor gets spliced into the red-black. I'm sure then the other end of the red-white which was cut earlier (but doesn't get joined to anything) you just tape up

    Then repeat with the other plug

    So leave the fan plugs connected up as normal, all the wires your playing around with are on the fan side, here's the same guide on a golf I believe with different pics, check from 6 onwards

    http://website.lineone.net/~alan.james.lorely/fan mod/Repair.html
     
  20. Crhome

    Crhome Active Member

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    Ok thx Kambo, I now know what I have done wrong. 1 thing am still confused about is sleeves. Where are the sleeves and how do I splice 1 side of the resistor into black/red? Sorry am also very new to all this wiring in cars.
     

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