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Thread: e38 A/C Request

  1. #1
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    e38 A/C Request

    Im in the process of wiring up an engine conversion, the plan has always been to run the A/C although now that I am looking over the wiring diagrams I can see that the A/C request to the e38 PCM in factory form involves both the HVAC control module and the Radio/HVAC Controls.


    Is there a way to signal the A/C Request directly to the e38 PCM?

  2. #2
    Advanced Tuner HartRod's Avatar
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    I did a conversion on my 68 C10 and I just used a trinary switch to control fans based on high and low pressure. No signal is sent from the ECM.
    69 Suburban Bagged & Blown: http://67-72chevytrucks.com/vboard/s...d.php?t=200387
    68 Farm Truck build thread-LS3/6L80/TVS1900: http://67-72chevytrucks.com/vboard/s...d.php?t=358692

  3. #3
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    you can wire the A/C compressor straight to a switch for on/off functions. send 12volts to the to the high pressure switch then on the out side of the switch run it to the a/c compressor..

  4. #4
    Quote Originally Posted by HartRod View Post
    I did a conversion on my 68 C10 and I just used a trinary switch to control fans based on high and low pressure. No signal is sent from the ECM.
    can you pm me some info on the switch you used.

    thanks

  5. #5
    Advanced Tuner HartRod's Avatar
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    Quote Originally Posted by 6speedblazer View Post
    can you pm me some info on the switch you used.

    thanks
    I got my trinary switch from Vintage Air and used their instructions to wire it up.
    69 Suburban Bagged & Blown: http://67-72chevytrucks.com/vboard/s...d.php?t=200387
    68 Farm Truck build thread-LS3/6L80/TVS1900: http://67-72chevytrucks.com/vboard/s...d.php?t=358692

  6. #6
    preciate it. i will look into it.

  7. #7
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    So there's no real way to use the ECM to shut off the AC compressor if you didn't want it to run at WOT or something? You'd have to wire it manually with a switch to turn ON/OFF the AC?

  8. #8
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    Would you guys be interested in a device that connected to the high speed lan connections and simply sent a repeating message of a/c request when powered up??

  9. #9
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    Quote Originally Posted by tek1229 View Post
    Would you guys be interested in a device that connected to the high speed lan connections and simply sent a repeating message of a/c request when powered up??
    OH HELL YEAH!!!

    lol. So I also had to deal with this exact problem on my LSA swap. I'm using a stock CTS-V E67 and a stock CTS-V BCM. My car originally had the Bosch E69 ECM and a totally different BCM. The problem is the factory HVAC control head in the Kappa's had an analog output to the BCM, the BCM converted it to a LAN command and sent it to the ECM for compressor request. The way I fixed it was kind of clunky, but it worked. I had a few old HVAC control heads laying around so I just took one from a late model GMC that also used the E67 and I'm using it as a "dummy" control head on the LAN line, sending the A/C request to the ECM. I still use the factory Sky control head in the dash, the analog output for A/C request simply turns on the other control head and it sends the request signal.

    So yeah, that would absolutely be something people could use. It's a common problem I've run across many times on putting crate engines in older cars, etc. Make me up one and I'll give it a try! And yes, like guys have said, it definitely works better if the ECM sends the A/C compressor request to the compressor clutch relay. That way you have control over high and low pressures, and of course it turns off the compressor at WOT.

  10. #10
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    Ditto on this sounding cool. I need to check how my car's AC controls work, and see if you could make something to work with it.

  11. #11
    Can you make such device?

  12. #12
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    Can you use the option in the menu's to change to a discrete AC output? Would you need to add a pin for that request to be sent, or what pint would it be from? Is there somewhere in the software code to see what pin it would be trying to output the signal to?

  13. #13
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    Quote Originally Posted by tek1229 View Post
    Would you guys be interested in a device that connected to the high speed lan connections and simply sent a repeating message of a/c request when powered up??
    Did this every happen? I'd be super interested in this!

  14. #14
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    Any update on this device?

  15. #15
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    My dad got one of these to try in his LS3 swapped Jaguar. I think he's planning to charge the AC this week or next week. So we'll see how it works.

    http://www.rpmextreme.com/Product/23...st-Module.aspx

  16. #16
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    Quote Originally Posted by brawls43 View Post
    My dad got one of these to try in his LS3 swapped Jaguar. I think he's planning to charge the AC this week or next week. So we'll see how it works.

    http://www.rpmextreme.com/Product/23...st-Module.aspx
    Cool. I'm hoping the serial data signal is the same on the e38 as it is on the e40. If it is, this will work.