CX Series 2 / cabin fan
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  1. #1
    Member cammells's Avatar
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    Default CX Series 2 / cabin fan

    Hi all,

    Hopefully an easy one?

    When I hopped into the CX this morning for my daily commute, I noticed that the cabin fan did not come on as it normally does when the ignition is switched on...

    The fan does run, however, on full, just not on the intermediate speeds. So it is not a problem of power to the fan itself, more the speed control. None of the intermediate speeds work, just maximum.

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    Can anyone point me in the right direction to rectify this ... i.e. what needs to be dismantled, and what the likely culprit is?

    thanks!
    Simon

  2. #2
    Real cars have hydraulics DoubleChevron's Avatar
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    I've never had it happen, but it'll be the transister on the controller board. If your lucky it'll just be a dry solder joint.

    I'll go do a search on the CX lists and see if I can find the replacement transistor they suggest.

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/citro%EBn-forum/90325-best-project-car-you-have-ever-seen.html
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
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  3. #3
    CitroŽn, what else? smiffy1071's Avatar
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    Yes, I think the transistor is the top suspect.

    You will need to remove the glove box, complete, and reach up behind the dashboard towards the widscreen, to find it.

    It's been a long time since I last saw one, (so my memory isn't that great) There is a transistor about the size of a 10Ý coin, that lives on a circuit board, with a multi plug.

    This controls the variable part of the fan, while full speed is on a separate circuit and relay.

    At least......I think that's how it goes!
    2005 C5 2.0 VTR Hdi 138, 1986 Kawasaki GPz 750G2

  4. #4
    Member cammells's Avatar
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    thanks Shane, Smiffy

    I can see where these components are now in the haynes manual ...

    658 for the transistor and 745 for the relay.

    Are there any tricks to getting the glovebox out or, more particualrly, getting it back in??

    cheers Simon

  5. #5
    CitroŽn, what else? smiffy1071's Avatar
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    I've done it once or twice, and it's a pain in the......
    Taking it out is quite easy, but getting it lined up for bolting back in, is the hard part.
    If my memory serves, it's just a 10mm spanner, and possibly a philips screw driver?

    Do it carefully though, I got something wrong last time I did it, and nearly set fire to the car!!
    I guess a wire got chafed on the steel framework...
    2005 C5 2.0 VTR Hdi 138, 1986 Kawasaki GPz 750G2

  6. #6
    Member cammells's Avatar
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    I've finally got around to looking at this job.

    I've found a reference to repairing the fan on the following site;

    http://www.citroen-cx-club.com/technik/fan.pdf

    This references upgrading the transistor to a Darlington MJ11033.

    Being an auto electrical novice, I've no idea whether this is a sensible modification or not (main reason I ask is that this transistor is listed on e-bay as a 120V 50A 300W resistor, not 12V as I probably would have thought?)

    Any thoughts appreciated...

    cheers Simon

  7. #7
    1000+ Posts Greg C's Avatar
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    That is the maximum figures the transistor can handle, so it will be having an easy life controlling the fan in your car. That is what you want surely
    Mine

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    Toyota Prius

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  8. #8
    Member cammells's Avatar
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    thanks Greg, makes sense.
    cheers Simon

  9. #9
    Member cammells's Avatar
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    I got around to doing some further work on the cabin fan today.

    The document referred to earlier in the thread recommended that the original transistor could be replaced with a "Darlington MJ11033" which I was able to source. I replaced the transistor today and the new one works, which I was very happy about.

    One thing I have noticed is that the transistor does get very hot ... therefore a couple of "electronics" questions:

    - why does the transistor get so hot (it is very hot to touch once it has been operating)?
    - does anyone think it essential to fit the cooling fin described in the attachment? i.e. is this transistor going to be running hotter than the original? The wiring to the fuel injection control unit is very close to the transistor (though not touching).

    thanks! Simon

    kind regards, Simon

  10. #10
    Real cars have hydraulics DoubleChevron's Avatar
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    The transistor gets hot as it's carrying a lot of current. Yes a heat sink would be a good idea, use heat sink paste and it'll probably last the life of the car

    Also check the earth point. Being a transister it's going to drop 1.4volts across the PNP/NPN junction. The "click" when you select the highest fan speed is a circuit that bypasses the transister (otherwise your maximum fan voltage would be 1.4volts less than it should be). I found this ground was suspect, so I added a second ground point. The fan controller setup is in the earth circuit of the fan, until you realise this trying to understand how it's working is difficult

    seeya,
    Shane L.

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  11. #11
    Member cammells's Avatar
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    Default cabin fan transistor

    I've added a heat sink as in the photos, and its working nicely... I've been told that the heat transfer through the front face of the transistor won't be that good as it's thin metal, however I figure it will be better than not having the extra heat sink.

    cheers Simon
    Attached Thumbnails Attached Thumbnails CX Series 2 / cabin fan-cx-series-2-transistor-1.jpg   CX Series 2 / cabin fan-cx-series-2-transistor-2.jpg  

  12. #12
    1000+ Posts Greg C's Avatar
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    That should help a lot. Bear in mind that silicon transistors can handle running quite hot. Rule is if you spit on them and they spit back, that is too hot. So they are quite happy at around 135C which is definitely too hot to touch
    Mine

    CX Prestige
    Toyota Prius

    In the family

    Xantia SX

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