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Thread: AC Fan Switch Ground

  1. #1
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    AC Fan Switch Ground

    It has been forever since I have posted here.
    Anyway I have had my Pro5 since new in 02. Still driving it with 200K+ miles on it.
    I finally figured out what the issue is with the fan switch that it seemed many a while ago were having. The ground connection for the fan switch is not a good one.

    I wired in a switch that I had laying around and ran a ground wire to a bracket under the dash and have had zero issues.
    In the picture you can see the wires with the yellow lug. One goes to the switch and the other the new ground. The factory connector is the original ground.

    Does anybody know where the factory ground goes? I can see that it goes under the drivers side some where but from there I don't know. I would like to fix the factory ground connection so that I don't have to get creative with the wiring unless I have too.

  2. #2
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    I soldered in 1/2" braid to the ground wire and took that to the frame and its all good now. Still a slight blink at position 2, so I will replace the switch.

    I was measuring 1.5 ohms from the ground to the negative terminal of the battery, which is way too much for a short wire like that.
    With the braid it now measures <0.5 ohms.

  3. #3
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    Still had some issues with position 2 on the fan switch. Ordered a new one from Mazda and its all good.

  4. #4
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    I have replaced my switch twice so far, and the latest one has only been in for about 2 years and it is bad.

    The most recent new switch started having problems with position two blinking at the end of the summer last year, and now it only works in position 1, or in between 3 and 4. It is so annoying.


    I think I remember a how-to a bunch a years ago where someone looked up the actual ohmic value of each position, removed the connector, and hardwired resisters to the wires.

    I might try to find it and do this, as replacing the switches is a pain.

  5. #5
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    Hardwired resistors might or might not work. Since the issue is the ground adding resistance and changing the voltage the ECU reads as being out of spec.
    There was also a thread on a forum where somebody added some active electronics to fool the ECU but this didn't address the actual issue of the bad ground.

    You could use some standard crimp connectors and jumpers and a "T" for the ground wire and test it out. That's what I did originally to lead me to this permanent solution. You still might have to change the switch if its too damaged. Though it still might work as well.

  6. #6
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    Mazda, Protege5

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    I am not doubting the ground issue at all, but according to many things I have read in the past, the issues had to do with the ohmic value changing of the resisters themselves.

    Of course, if the guide I saw before if they hardwired a ground, instead of using the existing one, then I guess that could have fixed the issue like in your example above.

    Maybe it is a combination of the ground and the resister going bad? Because if it was just a grounding issue, then a new switch probably wouldn't (temporally) fix the issue.

    Either way, this switch is annoying, and of course when one needs it fixed, it is crazy hot outside. Maybe I will just deal with mine until the fall.

  7. #7
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    If its the blower motor resistors, you can get a new resistor pack and swap that out. Would be easy and cheap to do. I did this and it didn't change anything for the operation of the AC.
    By hard wiring resistors you reduce the slight parasitic resistance for the wire and connectors from the switch to the resistors and back.
    There was another fix where the person crimped and soldered the wires directly to the switch which again helps but doesn't fix the main issue.
    The switch goes bad due to arcing and heat (from current) through the switch.

    Run your AC on 4 and see how hot that ground (black) wire gets.
    It would actually be interesting to measure the resistance from the switch connector to the negative on the battery to see what it measures.

  8. #8
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by crackerkorean View Post
    The switch goes bad due to arcing and heat (from current) through the switch...
    ^^^ what he said...
    That switch is only good to handle about one amp.
    It gets hot and conducts the heat up the wires.





    I still had continuity through the switch so I wired it up to relays, reducing the current through the switch to 20 milliamps.

    The Diagram Dude

  9. #9
    The Diagram Dude pcb's Avatar

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    And Don't Forget The Best Fix Of All !!...

    It's redneck approved !!

    Sigs are visible only in your first post on a page. To change your thread display preferences, click here and enable 'Always Show Signature'.

  10. #10
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    I would actually be interested to see what resistance to negative on the battery is for several owners.
    Before I did the mod it was >1.5 ohms, after <0.5.
    If I can I will try to get a picture of the ground braid that I installed when I install the new bezel.

  11. #11
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    Quote Originally Posted by crackerkorean View Post
    I would actually be interested to see what resistance to negative on the battery is for several owners.
    Before I did the mod it was >1.5 ohms, after <0.5.
    If I can I will try to get a picture of the ground braid that I installed when I install the new bezel.
    If I get some time, I will check it out. I am curious.

    If a new ground and a new switch fixes the issues, that would make be very happy.

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