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Thread: AC Fan Switch Ground

  1. #16
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    protege5

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    Yes.. I changed my mind lol. I live on a very dusty dirt road. I took the switch apart, cleaned it and it worked great for a couple months then started failing again. So i cleaned it again, its as if I never touched it to begin with. So, desperate for my AC to work correctly, I wired up the resistor hack. It's worked like a champ ever since. The blower resistor should be taking on all of the heat. You could measure with a meter but I am sure the switch itself is more than capable of handling the current demand. it's a solid copper bus bar, not a stranded wire. just like your ignition switch.

  2. #17
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    If i get a chance I will post the wiring diagram for the fan switch tonight.
    The ground point is the high resistance point that was putting the AC sense line out of spec.....i think. But since I cannot find it and look at it directly I cannot say 100%.

    What got me down this path was the over heated wires and somebody elses proposed fix where they used a couple of transistors to force a correct sense voltage. I saw this as a case of fixing the symptoms and not finding the source of the problem.
    I am not familiar with the resistor fix in detail so I cannot really comment on exactly what is going on. Maybe its a degrading connection between the resistor pack and the switch that is actually causing the issue. They use higher wattage resistors and basically force cool them with moving air so they don't pop.


    pb4ugotobed: This added resistance inside the fan switch itself is why the voltage drops as much as it does, to put the "AC Sense" circuit out of range, and turning off the compressor (AC light turns off).
    I don't completely disagree with this statement, yes the resistance between the switch contacts goes up as arcing occurs and carbon builds up. I still think the bad ground connection is more of a culprit vs the switch. It would essentially add another small resistor between the switch and ground moving all of the voltages from the switch up. I could be wrong though, kind of comes with engineering.

    I think I mentioned above that while on 4 the ground lead still gets warmer than I would like. And this is with everything working correctly. I am not familiar with the resistor mod. I wonder what it actually changes in the circuit to make things work vs what the factory has.


    Looking at the data sheet for a quick connect wire terminal, I cannot find what I think is a reasonable current rating (only example is 250A), its more of a max operating temperature (221f). This is the type of connector used in the factory switch. I was looking to see if I could possibly back out a current rating of the switch itself.

    You can get high currents through a PCB easy enough 10A but the trace needs to be 300+mil wide.

    In the end there might be different solutions, but I am trying to find the source of the problem.
    Last edited by crackerkorean; 07-24-2018 at 09:48 AM.

  3. #18
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    Quote Originally Posted by pb4ugotobed View Post
    Yes.. I changed my mind lol. I live on a very dusty dirt road. I took the switch apart, cleaned it and it worked great for a couple months then started failing again. So i cleaned it again, its as if I never touched it to begin with. So, desperate for my AC to work correctly, I wired up the resistor hack. It's worked like a champ ever since. The blower resistor should be taking on all of the heat. You could measure with a meter but I am sure the switch itself is more than capable of handling the current demand. it's a solid copper bus bar, not a stranded wire. just like your ignition switch.
    https://www.mazdas247.com/forum/show...3-quot-problem

    Is that the resistor mod that you did? This just forces the voltage on the sense wire to be within range. This doesn't fix the problem itself.

    With my original switch and creating a better ground, I was able to get 3 to work all the time and 2 to work some times. I haven't opened the switch to see what the condition of the contacts are in, so I imagine that's part of the issue that I was experiencing after getting a better ground. With the new switch it works 99.9% of the time. I had one hiccup on 2 when the inside of the car was really hot.

    I suspect that there are other connection points etc that might not be the best, and being a budget oriented car I would not be surprised.

  4. #19
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by crackerkorean View Post
    https://www.mazdas247.com/forum/show...3-quot-problem

    Is that the resistor mod that you did? This just forces the voltage on the sense wire to be within range. This doesn't fix the problem itself.
    Yea that's the resistor mod. And I don't like it either... Everything still gets hot.

    My relay pack has been working great for over 6 years now.

    BTW... Mazda did upgrade the switch in later models. It's a bit beefier inside and works a bit better.
    I'm pretty sure a replacement switch from Mazda would be the better one.
    The Diagram Dude

  5. #20
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    protege5

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    Quote Originally Posted by crackerkorean View Post
    https://www.mazdas247.com/forum/show...3-quot-problem

    Is that the resistor mod that you did? This just forces the voltage on the sense wire to be within range. This doesn't fix the problem itself.

    With my original switch and creating a better ground, I was able to get 3 to work all the time and 2 to work some times. I haven't opened the switch to see what the condition of the contacts are in, so I imagine that's part of the issue that I was experiencing after getting a better ground. With the new switch it works 99.9% of the time. I had one hiccup on 2 when the inside of the car was really hot.

    I suspect that there are other connection points etc that might not be the best, and being a budget oriented car I would not be surprised.
    Yes that's what i did.

    if it breaks again in the future i'll look further into it then. but it's been working great for 2 years now like that with zero issues. ultimately, i don't really care as long as it works lol. it's an old car with 260k miles on it. as long as it's blowing cold and the car runs/drives i have no plans to change anything unless it breaks

  6. #21
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    I think the relay mod that PCB did is the best solution. It keeps any current from going through the switch and thus keeps any arcing etc away and the relay is more than capable if handling any current etc. Being the type of person I am I like to find the root cause if an issue.

    Does anybody know if the behavior of the compressor changes based on the fan switch position?

  7. #22
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    protege5

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    no. the compressor behavior is controlled by pressure. it is not variable, it's either on, or off. fan speed just changes the amount of air flow across the evaporator. AC will actually blow a few degrees colder in position 1 vs. position 4 because the airflow is reduced, and the air is more "saturated" by the cold for lack of a better term. But compressor operation itself is either on or off.

    The only way fan speed MAY have a SLIGHT impact on compressor operation is just cycling because as the evaporator changes the refrigerant back to a gas, the increased airflow could speed that up slightly causing the pressures to vary some, so that could cause the compressor to be on more frequently or for longer periods of time but that's really grasping at straws.

  8. #23
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by crackerkorean View Post
    I think the relay mod that PCB did is the best solution. It keeps any current from going through the switch and thus keeps any arcing etc away and the relay is more than capable if handling any current etc. Being the type of person I am I like to find the root cause if an issue.
    I think the root cause is the switch. The wires in the connector were burnt and crispy for about two inches from the switch then the wires were OK.
    That suggests to me that the heat was in the switch and conducting along the wire.

    Here's a diagram that I made of my relays.. It might help you build one.





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