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  • Both fans coming on at same time

    I have the settings at 185/190 on the ECU, but I noticed both fans coming on at same time. I have an extra relay for the a/c input and wired according to the diagram in the linked post. And per my inquiry and Nates answer, 87 & 30 are swapped on both fan relays. I'm not much of an electrician, but it looks like if I have #85 on both fan relays wired to #87 on the a/c override relay, that fan 1 will ground fan 2 at the same time. If this is the way it is, I could eliminate fan 2 relay, run both fans on the fan 1 relay? Or am I looking at this wrong? Thanks.
    https://forums.edelbrock.com/forum/p...iring-question

  • #2
    That diagram is wrong......both fans will come on at the same time.

    Post "exactly" what you would like to do, and I'll draw you out a diagram.
    In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.

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    • #3
      Have fans 1 & 2 work individually through the ecu, have both fans come on when I turn the a/c on. Thanks

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      • #4
        Corky

        Each relay is just a switch that requires 12v+ and ground to flip. Because you have two fans, I would assume you want one running at 185 and then the second to turn on at 190. This is so close together, you COULD wire them to a single switch, BUT the basic Bosch style relay MAY burn up with too much current. So you should use two separate relays or buy a high current 75amp relay if you combine them.

        The AC override turns on both fans when the AC compressor is engaged. This is a good idea, but you may not need both fans to engage for this reason, and therefore could just make it engage a single fan. Because your wiring diagram is wrong (as BITE_ME pointed out), the two grounds are tied together right now. Therefore BOTH engage at 185. Easy Fix, just remove the ground lead from the AC override to the FAN 1 ground. This fixes your diagram (provided you wired the battery to 30 and not the 87 pins).

        Suggestion: Remove the FAN 1 to AC ground as above, set the high/fan2 temp to 195-200f, and you are all set. If you DO want both fans to engage when the AC compressor turns on, you will need another relay or diode to separate the two grounds.

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        • #5
          Okay, I already have 3 relays, don't want another. Didn't think about a diode, I know what they do. I'm about to be gone for the afternoon, will look at how to wire in a diode. Thanks.

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          • #6
            Originally posted by CorkyE View Post
            Have fans 1 & 2 work individually through the ecu, have both fans come on when I turn the a/c on. Thanks
            Do you want, say a 5 second delay, when you first turn on the motor?
            In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.

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            • #7
              Originally posted by BITE_ME View Post

              Do you want, say a 5 second delay, when you first turn on the motor?
              I do,I'm in a similar situation. I don't like the combined inrush if dual fans kicking on simultaneously at idle.

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              • #8
                Originally posted by BITE_ME View Post

                Do you want, say a 5 second delay, when you first turn on the motor?
                No Sir, fan 1 come on at set point, fan 2 come at set point, and both fans on with a/c switch.

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                • #9
                  Originally posted by Heatsoaked View Post

                  I do,I'm in a similar situation. I don't like the combined inrush if dual fans kicking on simultaneously at idle.
                  Yep, when both come on at same time, it's a drag - on the old alternator. I'm still reading 13/13.1 with both fans on.

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                  • #10
                    CorkeyE. I can do yours with no diodes. Will need to use 1 regular relay for each fan, and 1 special relay ( it's not that special really ) for the AC.....it will fix that diagram you posted.

                    Heatsoaked. I'll do yours with a 0-30 second timer between the 2 fan relays.

                    I'll also do a couple of other ones too.
                    In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.

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                    • #11
                      Thanks Bite Me, I think I have this worked out with a DPDT relay. This relay will replace the a/c override relay and allow fans to be controlled through the ecu when a/c is off. Thanks again.

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                      • #12
                        I appreciate it Bite_Me! I have sufficient alternator power, it's just that the IAC tries to make a big adjustment to rebound at idle when both the Spal 12 inch fans kick on together ( and the compressor ).

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                        • #13
                          Just to update; I used a DPDT switch in place of the a/c input relay. All is working as it should - fans come on individually at set points, and both come on when a/c is turned on.

                          I had some help from a member at NastyZ28.com and if anyone wants a diagram, I can send it to you.

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                          • #14
                            thank you for posting the fix. and yes please post the diagram for all of us.

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                            • #15
                              I don't have a web photo hosting site. I can email you a diagram if you want.

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