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Doesn't like my new AC addition. Surging, sometimes stalls?

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  • #16
    Is your ECM wired directly to the battery per the instructions? I overlooked this and initially wired mine to a common 12 volt positive post on the firewall. When driving with the headlights on my engine would surge every time I hit the dimmer switch. It may be that your new AC is putting some kind of spike in your 12 volt supply to the ECM?
    Last edited by ZZ6 EFI; 05-24-2021, 04:56 PM.

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    • #17
      Just thought I would post an update. I never did get this setup to where I am happy with it. I plan on building a new motor for it in a year or two, so I will deal more in depth then (I just have a higher idle all the time now), but I think it's a shame they cut a corner with AC hookups in the PF4. Whether or not you think the ecu can compensate quick enough, since the ECU has no way to monitor AC input/outs, you have to splice into your fan circuit (instead of the ECU triggering the fans, that are already controlled by the ECU), nor will it disable the compressor at WOT, to prevent overspinning the compressor, as well as power. For the other project car (very different car), I will try to retain and reflash the stock ECU/efi as a standalone ecu, and we'll see how that goes.

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      • #18
        Cutting corners? Lol. When my compressor cycles it also kicks on two 39 amp fans. The IAC and ECU and whatever else you want to call on compensate IMMEDIATELY! Not sure why yours is different.

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        • #19
          Originally posted by Heatsoaked View Post
          Cutting corners? Lol. When my compressor cycles it also kicks on two 39 amp fans. The IAC and ECU and whatever else you want to call on compensate IMMEDIATELY! Not sure why yours is different.
          Mine also, no lag, no drag.

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          • #20
            Originally posted by Stangman View Post
            Just thought I would post an update. I never did get this setup to where I am happy with it. I plan on building a new motor for it in a year or two, so I will deal more in depth then (I just have a higher idle all the time now), but I think it's a shame they cut a corner with AC hookups in the PF4. Whether or not you think the ecu can compensate quick enough, since the ECU has no way to monitor AC input/outs, you have to splice into your fan circuit (instead of the ECU triggering the fans, that are already controlled by the ECU), nor will it disable the compressor at WOT, to prevent overspinning the compressor, as well as power. For the other project car (very different car), I will try to retain and reflash the stock ECU/efi as a standalone ecu, and we'll see how that goes.
            The MAP sensor tells the system that you have a bigger load on the motor. So it compensates to keep the idle speed up.....IAC will open more for the same idle speed.

            How in the world would it know to turn on the fans, in less you told it to?

            Use a vacuum switch ( opens on low vacuum...wot ), or a mechanical switch ( normal closed, but opens when triggered ) on the throttle lever. With the switch connected in series, with the clutch wire......just like how factory cars did......they also would put a temp switch on the clutch wire. So the AC would not turn on till the motor was hot....i believe 175F was normal. It could have been 180F.
            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.
            https://forums.edelbrock.com/filedat...?photoid=42773

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            • #21
              I am installing a PF4 on a project with AC. An input for AC ON to the ECU would be nice to force ON a fan before the engine temp calls for it but..... I have dual electric fans. My plan is to add a third relay. Activate it with the AC compressor ON signal and wire the relay contacts to ground one of the existing fan relays. Anyone have any experience with this? see any concerns with grounding the ecu fan output before it calls for it?

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              • #22
                Originally posted by 69venture View Post
                I am installing a PF4 on a project with AC. An input for AC ON to the ECU would be nice to force ON a fan before the engine temp calls for it but..... I have dual electric fans. My plan is to add a third relay. Activate it with the AC compressor ON signal and wire the relay contacts to ground one of the existing fan relays. Anyone have any experience with this? see any concerns with grounding the ecu fan output before it calls for it?
                https://www.youtube.com/watch?v=cNs4OmfCjHw

                Don't get too caught up in the numbers.
                Just give the Engine what it wants &
                Let the numbers be what they are.

                Jim McFarland....

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                • #23
                  Originally posted by 69venture View Post
                  I am installing a PF4 on a project with AC. An input for AC ON to the ECU would be nice to force ON a fan before the engine temp calls for it but..... I have dual electric fans. My plan is to add a third relay. Activate it with the AC compressor ON signal and wire the relay contacts to ground one of the existing fan relays. Anyone have any experience with this? see any concerns with grounding the ecu fan output before it calls for it?
                  Instead of going off topic in this thread, start another thread and I'll post how to set up a DPDT relay. I tried the way you're describing and with a/c off, both fans come on when the system calls for the first one to turn on. Someone may have some other voodo that works better though.

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                  • #24
                    Screenshot_20210713-101705.png

                    As a side note and a totally incidental finding:

                    Due to my high-end stereo system, I thought I'd add a 1.5 farad capacitor to my amplifier power distribution block. Little did I know that this would have a beneficial effect on other accessories in the charging circuit. Specifically, when the dual spal fans kick on and off with the temp controller or cycle with the AC compressor, it buffers the current in-rush which smooths the IAC response. It's basically unnoticeable now
                    Last edited by Heatsoaked; 07-13-2021, 10:19 AM.

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                    • #25
                      SchematicPF4 with AC schematic.png

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                      • #26
                        Sorry for going off topic. Ill review video. Thanks

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                        • #27
                          Originally posted by Heatsoaked View Post
                          Cutting corners? Lol. When my compressor cycles it also kicks on two 39 amp fans. The IAC and ECU and whatever else you want to call on compensate IMMEDIATELY! Not sure why yours is different.
                          Yes, that is a corner cut. Not sure why you'd take it personally. My fans kick on immediately as well, because I have them wired to do so, by triggering the fan relays on the AC clutch circuit. That is very different than the ECU getting a signal that the AC is being engaged, and the ECU kicking on the fans, and the compressor being engaged by the ECU (and disengaged at WOT). And I see that's fine and acceptable for you, which is fine. But to argue it, is just looking to argue for the sake of it.

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                          • #28
                            Keep it simple. If it works, don't complicate it. Now drag racing at WOT is just plain silly with the AC on. Lol

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