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Thread: Holley EFI Control Of A/C Clutch

  1. #1

    Default Holley EFI Control Of A/C Clutch

    Finally getting around to setting up my A/C with my Holley EFI. Think this should work fine, but just wanted to get opinions. The main reason I set it up like this, is so I can also control my PWM signal for my radiator fan based on the A/C being turned on too. I have it setup wiring wise like this:
    A/C signal out of Dash
    Runs through the low pressure switch (so no A/C if R134 pressure is too low).
    From there it goes to an input on the Holley ECU (B12).
    Then I have an output from the ECU (A12) that triggers a relay that controls the A/C clutch.

    Then software-wise I have my output set up like this:
    Basically the A/C will engage if all parameters are met.
    -Dash signal is on
    -TPS is under 50%
    -RPM are above 600
    -RPM are under 4000

    Last edited by TxFireman1972; 08-08-2017 at 12:11 AM.

  2. #2


    I think you are on the right track. See Donny's post here: You can probably set TPS at 75% or lower. Andrew

  3. #3


    Thanks Andrew. Does the IAC Kick have to have its own dedicated input pin? Would like to just have it activated by the Dash A/C signal input I have coming into B12 already. I haven't been able to find a way to achieve that yet though. Looks like I have to assign it to its own pin. I'm just trying to minimize my inputs/outputs, since I'm running the HP not the Dominator. I do have my A/C signal coming from my Dash controls setup as a Custom 20V like you showed in one of your posts. Is there any way possible to just use that input to activate my IAC Kick function instead of adding another input just for the IAC Kick?

    Last edited by TxFireman1972; 08-08-2017 at 12:53 PM.

  4. #4


    I think I figured it out. I realize now that it's possible to stack more than one item on a single pin. But they have to be the same type (12+, ground). Since my A/C signal coming from the dash is setup as a Custom 20V input, it won't let me add the IAC Kick to the same pin, because it's a 12+.

    So I guess my best option is to just wire in another input for the IAC Kick. That way I can still maintain my ability to turn the fan on anytime the A/C is turned on through my PWM Table, as shown above. I have the extra pin right now, so it's not a big deal. I can look at other options later if I need the pin for something else.

    I should be able to just connect both input wires (from the I/O Harness) to the same wire coming from the dash controls, right? Or would they interfere with each other?
    Last edited by TxFireman1972; 08-08-2017 at 01:31 PM.

  5. #5


    Why do you need the IAC Kick? Do you actually want to have a higher idle speed when the A/C is on? If not, then the IAC will compensate for the A/C load and keep the idle speed wherever you have it set in the Idle ICF. Andrew

  6. #6


    Honestly, just because I've had people tell me I need it, LOL. I'll definitely give it a try without.

  7. #7
    Join Date
    Dec 2009


    Quote Originally Posted by andrewb70 View Post
    Why do you need the IAC Kick? Do you actually want to have a higher idle speed when the A/C is on?
    The A/C "IAC Kick" function only produces a momentary increase in IAC, so the engine RPM doesn't dip down when the A/C is turned on (or in your case, electric fans). It works fine, but it does not increase & hold the idle RPM like a high idle function. Actually, the IAC Kick function is usually not necessary. It's typically a tuning issue with the Base Fuel Table. If you need a high idle function, it can be programmed in the V4 EFI software Advanced ICF (1D Table, "Target Idle Speed Offset" Table Type, Switched Enable Activation) to use as a high idle switch.

    If not, then the IAC will compensate for the A/C load and keep the idle speed wherever you have it set in the Idle ICF.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

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