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Thread: Fan Relay Control

  1. #11
    Senior Member Bitsyncmaster's Avatar
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    You would need 12 volts or better a little higher that can drive about 60 to 80 ma. to turn the fan relay on by just spicing into that otterstat wire. Not sure is your "NO2" circuit can drive that.
    Dave M vin 03572
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  2. #12
    EFI'd dn010's Avatar
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    Turns out I couldn't use the N2O wire I wanted as it was only an "IN" and could not be used for voltage out. So, I used a sequential injector wire from the ECU to wire up a relay using the injector wire as a ground to make the relay function, sending +12VDC to the original fan relay and then the splice wire (fan fail) etc.

    I was trying to get away with not having to use yet another relay but I couldn't in the end. At least I have functioning fans now! Thanks again guys.
    Last edited by dn010; 01-25-2016 at 02:48 PM.
    -----Dan B.

  3. #13
    EFI'd dn010's Avatar
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    Sorry to resurrect this yet again but when you ran this circuit, did you have any power issues once you shut off the AC? If the compressor is engaged and I turn the mode switch to off, my battery light comes on for a moment and then turns off. Now that I have a clock installed, it will also reset the clock from whatever time to 12:00. This is starting to become somewhat of annoyance and I can't seem to figure out where this is coming from. I have a diode at the compressor. It's only when I turn the switch off, if the AC is cycling it does not give me any issues, same with the fan - the fans can cycle no problems.
    -----Dan B.

  4. #14
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by dn010 View Post
    Sorry to resurrect this yet again but when you ran this circuit, did you have any power issues once you shut off the AC? If the compressor is engaged and I turn the mode switch to off, my battery light comes on for a moment and then turns off. Now that I have a clock installed, it will also reset the clock from whatever time to 12:00. This is starting to become somewhat of annoyance and I can't seem to figure out where this is coming from. I have a diode at the compressor. It's only when I turn the switch off, if the AC is cycling it does not give me any issues, same with the fan - the fans can cycle no problems.
    I had a reset on my electronic battery relay when I turned the AC off but the zener diode on the compressor fixed that. A diode should also work. I would suggest you test that your diode is still working.

    The compressor clutch turning off puts out a negative 200 volt spike which probably gets into the grounds of the car.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #15
    EFI'd dn010's Avatar
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    Thank you. I will check that it is still operational. I never removed the factory diode so even if it isn't working, that diode should still be there. My confusion here is the clutch cycling on and off does not cause any abnormalities, it is only when I use the mode switch from any AC mode to off that creates this issue. If the diode was bad, wouldn't this happen when the clutch cycles too? I'll check the diode tonight along with some other things, I now wonder if I unhook the compressor and try the mode switch, if it would still create this problem.


    Quote Originally Posted by Bitsyncmaster View Post
    I had a reset on my electronic battery relay when I turned the AC off but the zener diode on the compressor fixed that. A diode should also work. I would suggest you test that your diode is still working.

    The compressor clutch turning off puts out a negative 200 volt spike which probably gets into the grounds of the car.
    -----Dan B.

  6. #16
    '82 T3 Turbo FABombjoy's Avatar
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    The factory diode keeps the otterstat from turning the ac compressor on. Diodes almost always fail open circuit, so if the factory diode was bad your fans would not turn on with the AC. If it failed short your compressor would have a mind of its own.

    The schematic shows a noise suppression capacitor on the mode switch that might be defective or disconnected from ground.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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  7. #17
    EFI'd dn010's Avatar
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    Problem is, my setup is using a MS ecu, engine swap, etc. so I'm not even sure without looking at my car's specific wiring diagram I made, what changes I made or what I bypassed. I do know for sure I wired in a diode, in the wire going to the compressor. Interestingly, my radio hasn't worked for a while, no power, so maybe it is something going on behind the plate that needs attention. Just when you think you're all done with one area of the car....

    Quote Originally Posted by FABombjoy View Post
    The factory diode keeps the otterstat from turning the ac compressor on. Diodes almost always fail open circuit, so if the factory diode was bad your fans would not turn on with the AC. If it failed short your compressor would have a mind of its own.

    The schematic shows a noise suppression capacitor on the mode switch that might be defective or disconnected from ground.
    -----Dan B.

  8. #18
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by dn010 View Post
    Thank you. I will check that it is still operational. I never removed the factory diode so even if it isn't working, that diode should still be there. My confusion here is the clutch cycling on and off does not cause any abnormalities, it is only when I use the mode switch from any AC mode to off that creates this issue. If the diode was bad, wouldn't this happen when the clutch cycles too? I'll check the diode tonight along with some other things, I now wonder if I unhook the compressor and try the mode switch, if it would still create this problem.
    I mistook your diode comment to think you installed a suppressor that I recommended in a thread.

    http://dmctalk.org/showthread.php?12...pressor-clutch

    If you don't have that diode or zener I can 90% say that will fix your problem.

    Using the switch brings that voltage spike up to the center console. Normal AC the switching happens at the low pressure switch.
    Last edited by Bitsyncmaster; 04-10-2017 at 05:18 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #19
    EFI'd dn010's Avatar
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    Excellent read, thank you for posting this. I will see if I have the zener among my electrical components and if not I'll order it & install. Thank you again!

    Quote Originally Posted by Bitsyncmaster View Post
    I mistook your diode comment to think you installed a suppressor that I recommended in a thread.

    http://dmctalk.org/showthread.php?12...pressor-clutch

    If you don't have that diode or zener I can 90% say that will fix your problem.

    Using the switch brings that voltage spike up to the center console. Normal AC the switching happens at the low pressure switch.
    -----Dan B.

  10. #20
    EFI'd dn010's Avatar
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    Received the correct Zener diodes yesterday, I have a ton of them but not the number you posted. Installed it today and the problem disappeared! Thank you again for posting that Dave, one less frustration now. I am on to heat shrink wrapping the install now, always something to do. By the way, I haven't forgotten about ordering your dimmer relay, just need to figure out the rest of my alarm removal situation first, one of these days I'll be done.

    thanks again - Dan B.
    -----Dan B.

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