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Thread: 7730 A/C clutch control

  1. #1
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    7730 A/C clutch control

    so im troubleshooting my A/C wiring on the POS fiero, ever since I swapped to the 7730 the A/C hasnt worked. today I found out that the high pressure switch is toast, ill probably bypass it. and for some reason the ECM wasnt energizing the A/C clutch relay either. according to the fiero wiring diagrams, the ECM energizes the A/C clutch relay but means of ground triggering.

    the 7730 uses pin F1 to trigger the relay. One wire is 12V hot from the A/C controls and the other(to ECM) SHOULD be ground triggered. Well its not, the wire from the ECM is 12V hot as well. WTF! the wiring diagrams im using are for the TPI cars and show it as a ground trigger.

    The only thing I can figure is this computer may be different since its off a 92 J body car(V6). I also tried a backup 7730 out of another J car. Both ECMs send 12V to pin F1. Im going to look around for the J body wiring diagrams to see if its different from the TPI cars.

    Now heres the million dollar question, can I just reverse the polarity of the relay so that the wire that was orinally hot(HVAC controls) is now the ground? or will I burn up a foil layer(or something else) in the ECM?

    Thanks in advance!
    '86 Grand National

  2. #2
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    Also ,since im using $8D S_AUJP, and the wiring diagrams dont show the ECM as a trigger for the A/C clutch, does that mean something has to be changed in the code?
    '86 Grand National

  3. #3
    Super Moderator Six_Shooter's Avatar
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    Were you checking the voltage on the A/C pin with the relay plugged in and the A/C control set to a position that would provide the 12V to the relay?
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Quote Originally Posted by Six_Shooter View Post
    Were you checking the voltage on the A/C pin with the relay plugged in and the A/C control set to a position that would provide the 12V to the relay?
    Yes to all. With everything on and plugged in, both pins at the relay(for coil) are HOT. When I turn the HVAC controls to off, they both go cold. Same conditions when the relay is unplugged.
    '86 Grand National

  5. #5
    Super Moderator Six_Shooter's Avatar
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    Looking through my diagrams I see that F1 can be used for both the A/C compressor relay and shift light. It is definitely a ground trigger.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by 34blazer View Post
    Yes to all. With everything on and plugged in, both pins at the relay(for coil) are HOT. When I turn the HVAC controls to off, they both go cold. Same conditions when the relay is unplugged.
    The wire should be dead with the relay unplugged. With it plugged in, and the ECM not triggering the relay, there will be 12V on that wire between the relay and the ECM, this is normal, since the coil in the relay allows the voltage to be seen on both sides of the coil, when connected to only one side.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Quote Originally Posted by Six_Shooter View Post
    The wire should be dead with the relay unplugged. With it plugged in, and the ECM not triggering the relay, there will be 12V on that wire between the relay and the ECM, this is normal, since the coil in the relay allows the voltage to be seen on both sides of the coil, when connected to only one side.
    yeah nevermind, I just double checked with the relay unplugged and youre right. going to try a newer style relay to see if it triggers that.
    '86 Grand National

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    Just tried another relay and no joy. Both ECMs must be messed up or something because I can manually trigger the relay. for $8D pin F1 is for a shift light, could that be why F1 doesnt ground the circuit?
    '86 Grand National

  9. #9
    Super Moderator Six_Shooter's Avatar
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    Are you meeting all parameters to allow the ECM to trigger the A/C relay?
    The man who says something is impossible, is usually interrupted by the man doing it.

  10. #10
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    Quote Originally Posted by Six_Shooter View Post
    Are you meeting all parameters to allow the ECM to trigger the A/C relay?
    looking at wiring diagrams for $8D and in the hac, no A/C compressor relay controls at all. looks like a patch may be needed
    '86 Grand National

  11. #11
    Super Moderator Six_Shooter's Avatar
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    There should be no patch or anything of the sort needed.

    What I'm asking about is are all of the parameters that would be set in the ECM being met, such as RPM, A/C request, etc, etc?
    The man who says something is impossible, is usually interrupted by the man doing it.

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    91 firebird 5.7:

    http://i.imgur.com/IwDVFCz.png

    odd.... GM chose to have compressor operation controlled by the HVAC switch along with what looks like high and low pressure switches to shut the compressor down when necessary. the ECM only tracks the status of the compressor clutch. odd that not even a relay is used, all of the current goes through the HVAC switch.


    from the sounds of it, you're going to be doing some rewiring or patching SAUJP to monitor and act upon an A/C request signal.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  13. #13
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    Quote Originally Posted by Six_Shooter View Post
    There should be no patch or anything of the sort needed.

    What I'm asking about is are all of the parameters that would be set in the ECM being met, such as RPM, A/C request, etc, etc?
    Ive been looking through the definition and cannot find anything that controls the A/C clutch relay. Only items that relate to A/C are for IAC, fuel(pw?), and fan.

    A/C clutch relay is controlled on pin F1 with $88 and $A1, but for $8D that pin is used for the shift light.

    Now i can get the clutch to engage by grounding the circuit connected to F1.
    '86 Grand National

  14. #14
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    Quote Originally Posted by RobertISaar View Post
    91 firebird 5.7:

    http://i.imgur.com/IwDVFCz.png

    odd.... GM chose to have compressor operation controlled by the HVAC switch along with what looks like high and low pressure switches to shut the compressor down when necessary. the ECM only tracks the status of the compressor clutch. odd that not even a relay is used, all of the current goes through the HVAC switch.


    from the sounds of it, you're going to be doing some rewiring or patching SAUJP to monitor and act upon an A/C request signal.
    I can monitor clutch operation with the adx and it does show clutch engaged when I manually trigger the relay.

    other items in the datastream are: a/c req, a/c high pressure, a/c low pressure, a/c clutch indicator, A/C First Pass with HI MPH, and A/C Disabled via HI MPH
    Last edited by 34blazer; 05-12-2013 at 07:09 AM.
    '86 Grand National

  15. #15
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    Quote Originally Posted by 34blazer View Post
    looking at wiring diagrams for $8D and in the hac, no A/C compressor relay controls at all. looks like a patch may be needed
    No patch needed I was running dual fans and controlling my 83 G20s stock WOT compressor cutout relay with SAJUP v3 and stock AJUP. Just have to adjust the values in the constants because they defaulted disable. The $8D code also idles much better when controlling the a/c.

    IIRC it was used in a Vette application. I one had a 7730 to 7727 pin chart. For all practical elecrrical purposws they are the same ecm. If anyone has that chart its pin A13 in a 7727.

    Edit- I found my notes and it looks to have been on F3 maybe.
    Last edited by Fast355; 05-12-2013 at 04:53 PM.

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