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Thread: 2003-up Silverado AC request type

  1. #21
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    Thanks for adding this feature to your newest release!
    -Sean
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  2. #22
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    Quote Originally Posted by 99RegalGS View Post
    Thanks for adding this feature to your newest release!
    You are welcome
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  3. #23
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    x 2. Will be a handy feature.

  4. #24
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    Thank you!
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  5. #25
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    I have been looking into this a little bit and heres what I have come up with for our options.

    I`m not sure what would use the serial option but I believe thats a serial data request and a variable displacement compressor (not much use to us conversion guys)

    The serial cycling option is what is used on many of the blue/green PCM trucks like a 2003 suburban, it will expect a serial data request and have a cycling compressor.

    The analog cycling option is going to expect a +12v signal to connector C2 pin 17 for the A/C request and will probably need to be wired like a 2003 express van. Oddly the low pressure switch seems to send a ground signal to C2 pin 55 when the pressure drops too low. (I don`t have access to a 2003 express van or pressure sensor to confirm this.) The analog cycling option is going to be the most useful to us conversion guys as the older GM compressors were all cycling systems and I believe the vintage air is too.

    The analog option would be like the 98-02 f-body uses, where its a +12v request and has a variable displacement compressor with an actual pressure sensor to tell the pcm the exact pressure instead of just upper and lower cutout switches like the analog cycling.

    Passive?? I have no idea here.

    Not fitted... I can only assume this means all of the A/C requests and drivers are turned off.
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  6. #26
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    This is GREAT news for us. We do ALOT of standalone hot rod builds using the P59 controllers and this was one of the major deals to work around on the P59 was AC request type because to make it work correctly a BCM would have to be used before to send the serial signal to the controller. We will be testing this for sure! Thanks guys at HPT!!!
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  7. #27
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    Can anyone confirm the analog mode uses a 12v request? Looking at a stock 04 gto file, the default mode is "analog", yet I believe it does use serial data for the request. In my swapped g-body I am using electric fans and would like the ability to control the fans with ac through the pressure sensor and use a 12v request. I would like to hear if anyone has played with this option yet.

  8. #28
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    Quote Originally Posted by Tbrett View Post
    Can anyone confirm the analog mode uses a 12v request? Looking at a stock 04 gto file, the default mode is "analog", yet I believe it does use serial data for the request. In my swapped g-body I am using electric fans and would like the ability to control the fans with ac through the pressure sensor and use a 12v request. I would like to hear if anyone has played with this option yet.
    The GTO setting is correct - it's analog. The Suburban uses a HVAC control module, so it's serial. You can compare the attached diagrams for the two.

    gto.png

    suburban.png

  9. #29
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    Thanks for posting the diagrams. However, I still don't see a pcm pin for the 12v request on the gto schematic. From my research, the request goes to a bcm still and then is fed to the pcm via class II.

    Also, looking at the 03+ corvettes, they also have "analog" selected in the tune and they do not use a 12v request either. Using the analog cycling option like what is used in the 03+ vans gives the ability to use the 12v request, but it does not activate electric fans based on ac pressure. The vans only used mechanical fans. Ideally, it would be nice to use a pressure sensor like found in the 03+ trucks, vettes and gto and have it work with the 12v ac request. This would give us proper electric fan operation for the A/C.

  10. #30
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    Quote Originally Posted by Tbrett View Post
    Thanks for posting the diagrams. However, I still don't see a pcm pin for the 12v request on the gto schematic. From my research, the request goes to a bcm still and then is fed to the pcm via class II.

    Also, looking at the 03+ corvettes, they also have "analog" selected in the tune and they do not use a 12v request either. Using the analog cycling option like what is used in the 03+ vans gives the ability to use the 12v request, but it does not activate electric fans based on ac pressure. The vans only used mechanical fans. Ideally, it would be nice to use a pressure sensor like found in the 03+ trucks, vettes and gto and have it work with the 12v ac request. This would give us proper electric fan operation for the A/C.
    The output from the PCM in the second diagram is "Class 2" which is exactly what serial means. It's the means through which the PCM sends the "turn on" information to the next module. In the GTO case, it's not done through Class 2 communication.

  11. #31
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    Quote Originally Posted by caesar View Post
    The output from the PCM in the second diagram is "Class 2" which is exactly what serial means. It's the means through which the PCM sends the "turn on" information to the next module. In the GTO case, it's not done through Class 2 communication.
    OK, so how does an 04 gto receive the request? In the diagram you posted, there is no pin for the ac request.

  12. #32
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    Very nice, just saw that this was added. Just in time as I will be putting a 05 LQ4 into a 69 GMC in the next few weeks.

  13. #33
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    I usually search and research until I find my answers but I'm at a loss with this one. I have the updated version of hp tuners as of two days ago and I have the option to change the ac cycle type and have tried all types with no success. It's a 04 silverado lq4 pcm in a 91 s10 pickup. I have the ac wired like factory, the high pressure switch and compressor clutch, except the s10 low pressure switch triggers the positive side of the clutch relay. I wired c2 17 ,like express, to that same wire so it would send voltage to the relay and the pcm when I turn the ac on in the cab and the low pressure switch allows12v . Didn't work. how do I get the pcm to control the ac?

  14. #34
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    Please let me know what you find out peribuilder because I have a 5.3 from a 04 Suburban and a/c is the last thing I have to wire for my swap. Has anybody used this option successfully? Do you wire up the a/c like the vehicle the pcm came from? If so does it just change the a/c request from serial to analog? If this is the case how do you wire in the low pressure switch with a truck pcm because it goes to the hvac control unit and not the pcm?
    0996b43f8024192e.gif

  15. #35
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    I also sent this email to HP Tuners support:
    Me: So did you guys program the a/c request analog signal to work like a early truck where it uses a high and low pressure switch or a car that uses a 3 wire pressure sensor for the pcm to control the compressor? Thank you.
    HP:We don’t do any programming here. Hence the reason we don’t know the answer to your question.

  16. #36
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    I wired the pcm like the express van and tried every request type with no success. I bought a hvac control module from a 04 Silverado and wired the class 2 to it, put power and ground to it and it works. I put the request type back to serial cycling. Without a doubt worth all the trouble.

  17. #37
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    Quote Originally Posted by peribuilder View Post
    I wired the pcm like the express van and tried every request type with no success. I bought a hvac control module from a 04 Silverado and wired the class 2 to it, put power and ground to it and it works. I put the request type back to serial cycling. Without a doubt worth all the trouble.
    So are you using the Silverado HVAC module to control the hvac in your swapped car? What type of car is this in?

    edit: I just seen your previous post.

  18. #38
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    Just to send the class 2 signal to the pcm. The ignition wire to the Silverado hvac module gets 12v power from the low pressure switch which is still 91 s10. The Silverado hvac module has a orange battery wire that I put battery power to so once I press the ac button on it it has memory so I don't have to press it every time I turn on the ac.

  19. #39
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    Well after spending hours playing with HPTuners and a tech 2 I have found that the A/C request switch feature only partially works. You don`t have as much capability to change the A/C request type as the options in HPTuners would lead you to believe.

    I`m working with a 2003 blue/green pcm # 12576106 operating system # 12579405. This PCM and OS were used in both trucks/suv`s and vans with serial (trucks/suv`s) and analog cycling (vans) a/c request types. Since this PCM and OS was used both with the pressure switch and sensors and as a serial or analog cycling request I thought that I would be able to simply change my request type from serial to analog cycling, ground C2 pin 55, give +12v to C2 pin 17, and get the pcm to bump my idle and turn the fans on.

    Turns out the PCM would acknowledge the A/C request but would not bump the idle, energize the a/c relay or fans as it was looking for the pressure sensor signal not the ground from the low pressure switch. I was kinda pissed but realized this OS was also used in the vans....so I changed my platform type to GMT610. This did not work as it was still looking for the pressure sensor. I really don`t understand why as this OS was used in both trucks and vans. So I changed back to the GMT800 platform and added 2 100K resistors in parallel (I didn`t have any resistors between 47k and 100k on hand so the 2 paralleled 100`s make approx 50k) in place of the pressure sensor. Now I had the PCM accepting an 12v a/c request and the PCM was seeing ~228psi of pressure but it still would not bump the idle, trigger the clutch relay or the fans. I tried using the tech 2 to manually enable the clutch relay but it told me the A/C pressure was out of normal range. I tried using different resistors and varied the a/c pressure between 91 and 372 psi but nothing worked and the tech 2 always said the a/c pressure was out of range if I tried to enable the relay manually.

    Finally I changed my a/c request type to analog. That fixed most of the issues. Now with +12v to C2 pin 17 and the 2 100k parallel resistors between pin C1 45 and C2 pin 14 the PCM would trigger the a/c clutch relay and the idle would bump up. I still am not able to trigger the fans no matter where I set the fan 1/2 enable A/C pressure, but I know this truck had a mechanical fan from the factory so maybe it is impossible to trigger an e-fan based on A/C pressure with this operating system?


    Short notes:

    You cannot change your pressure sensor type. If your PCM ran a pressure sensor from the factory that is what you are stuck with. If it had high/low pressure switches your stuck with those. Even if your PCM/OS was used with either setup you cannot change between them with HPTuners.

    You can change your a/c request type up to a point. You can change between serial and analog or between analog cycling and serial cycling. You cannot change from serial to analog cycling or serial cycling to analog. HPTuners will let you make the change but the PCM will not function with it. I have no idea what the "passive" option does, maybe I will have time to try that one in the future.
    85 El Camino SS black and silver, factory buckets.
    5.3L/4l60E 3.73 posi
    1980 Chevette .....needs a V6 swap
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  20. #40
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    Would someone be willing to verify if a 2004 Vette Blue/Green PCM #12586243 with the Vette OS for RPO C60 (Manual AC) does indeed have the AC request signal on C2 (green) pin 17?

    Thanks,
    TJ