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Thread: fan fail light

  1. #1
    Junior Member
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    fan fail light

    Hi

    Is it normal for the fan fail light to flash on briefly every time the air con compressor engages ? Fans come on and run ok its just accompanied by the light for a brief moment and the clicking from the relays behind the seat. Do I need to buy the kow amp draw replacement fans ?

    Thank You

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Normally the fan fail unit has been removed and replaced with jumpers (as per recall notice). When that is done the fan fail light is not connected to anything. The original fan fail unit would turn on the fan fail light if the current of both fans dropped below 20 amps total. So assuming your still running the original fan fail unit, your voltage probably drops when the AC kicks on and therefor your fan currents drop for an instant.

    Now I have found when the AC kicks off there is a negative 200 volt spike that can get into the cars wiring and that has upset the voltage regulation in some alternators (and can cause other problems). Putting a diode or zener diode on the compressor clutch will remove that negative spike.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Delorean Guru
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    To answer that question it is helpful to know what is in the fan fail relay socket. The quick answer is NO, the light is not supposed to go on unless you have a relay in that socket that works and there is a problem with one of the fan motors. I would also verify none of the bulbs were mixed up in the console and it isn't the fan fail light lighting up.
    David Teitelbaum

  4. #4
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    Quote Originally Posted by David T View Post
    To answer that question it is helpful to know what is in the fan fail relay socket. The quick answer is NO, the light is not supposed to go on unless you have a relay in that socket that works and there is a problem with one of the fan motors. I would also verify none of the bulbs were mixed up in the console and it isn't the fan fail light lighting up.

    Blue relay in the fan fail socket. Both fans work as far as I can see but I do want to replace them with the new style fans.

  5. #5
    Delorean Guru
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    You really should not be using that relay. Very high failure rate. Probably the reason for the flickering light.
    David Teitelbaum

  6. #6
    Senior Member ramblinmike's Avatar
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    Quote Originally Posted by nickcollins View Post
    Hi

    Is it normal for the fan fail light to flash on briefly every time the air con compressor engages ? Fans come on and run ok its just accompanied by the light for a brief moment and the clicking from the relays behind the seat. Do I need to buy the kow amp draw replacement fans ?

    Thank You
    My car had the fan fail relay installed when I brought it home. It behaved the same way, with a brief flash (<1 second) of the fan fail light every time the fans turned on. On my car, it was every time the fans came on, not just when the a/c clutch engaged. At that time (2004) everything I read suggested eliminating the fan fail relay altogether.
    Yeah, it's dirty. I drive it.

  7. #7
    Senior Member Rich's Avatar
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    Quote Originally Posted by nickcollins View Post
    Hi

    Is it normal for the fan fail light to flash on briefly every time the air con compressor engages ?
    Yes, it's normal, at least for a D that's not had any fan relay/bypass/module updates. I think they all did that when new - I know ours did.

    And, as noted in the post before this one, it is something that happens on such D's when the rad. fans start up for any reason, including during A/C compressor engagement.
    March '81, 5-speed, black interior

  8. #8
    Administrator Ron's Avatar
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    The post HERE shows the fuses installed. (If one of them blows, it will point you to the problem fan/circuit in the future ;-)

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