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Thread: About to toss in goal on getting a/c to work.

  1. #1
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    About to toss in towl on getting a/c to work.

    We did a crate ls3 swap with a B&M 4l80 swap into a customers 04 v6 silverado. The drive by wire system would not communicate no matter what we tried so we ended up swaping to drive by cable. So now we have the factory v6 ecu in it but I can not get the ecu to see the a/c request signal. I have tried serial cycling and just straight serial. Any ideas?
    Last edited by shanevas2; 06-28-2019 at 07:23 AM.

  2. #2
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    No ideas?

  3. #3
    Senior Tuner mbray01's Avatar
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    We just did a v6 to v8 swap in an 05, using cable throttle. Everything works as designed. Using serial cycling. Are you certain there isnt another issue. Check the wiring

    what operating system are you using.
    Michael Bray
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    Ecm is 04 silverado flashed to 03 express van. I even tried changing platform type back to the GMT800 thinking that might be issue but no go. No matter what i do it will not see the request. I checked the pressure sensor and it is reading. The low pressure is working but i pulled dash apart and not getting a ground at the A12 pin from the low pressure switch. I tried grounding it to see if that would trigger it ans no luck. I can command ecu to turn on compressor and that works no problem.

  5. #5
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    The 2003 Express / Savana A/C systems are wired differently than the 2003 Silverado / Sierra. The vans used Low and High A./C Pressure Switches, while trucks use an A/C Pressure Sensor. The A/C Request signal in a van is a 12 volt input (PCM type is Analog Recycling), while trucks used Serial Data activation (PCM type is Serial Recycling).

    The A/C wiring and switches (or sensor) must match the PCM programming.

  6. #6
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    So what or would I be able to use that is drive by wire and serial ac? I tried wiring 12v and that did not want to work ether. Maybe I am just overly frustrated witg it. This truck has been nothing but issues.

  7. #7
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    If the vehicle is a 2004 Silverado (originally a V6), then it is likely best to program the PCM as a 2004 Silverado V8 - for many reasons - including maintaining the original V6 VIN.

    This would get you DBW throttle control (requiring a pedal and TAC Module from a 2003 to 2005 Silverado). The 2004 V6 and V8 Silverado used the same A/C configuration. An A/C Pressure Sensor, and an inline A/C Low Pressure Switch (mounted on the accumulator if memory serves) - as a secondary safety measure.

    The A/C Compressor Clutch is activated by the PCM (grounds the relay) after receiving a Serial Data message from the HVAC Module - as long as the A/C Low Pressure Switch is closed, and the A/C Pressure Sensor is within operating limits.

    Access to good quality schematics is always necessary with such projects.

    As mbray01 stated in post #3 - this type of conversion has been done by others and works fine.

  8. #8
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    We did that originally. The drive by wire system worked but would not communicate with ecu. We replaced with new everything. All voltage levels checked out, no shorts, power where it was supposed to have power but still code u0107 or what ever it is. This truck I think hs some vugs but have not been able to pinpoint them.

  9. #9
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    With a P59 PCM, a U0107 DTC means that the UART communications between the TAC Module and the PCM are not correct - either via wiring or programming (or both).

    The TAC Module and pedal must be from a 2003 to 2005 Silverado / Sierra with an LS engine. The PCM must be fully programmed - I don't use tuning software for this job.

    What is the Service Number and Hardware Number on the P59 PCM that you are using ?

  10. #10
    Senior Tuner mbray01's Avatar
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    this is your issue. on the trucks the hvac module receives the low pressure input, then sends signal to ecm via class 2 giving an ok.

    on the vans the signal is sent directly to the ecm via pin 55 on connector 2. the vans do not use the high pressure sensor circuit via a/c clutch actuation

    you need to wire that circuit from the low pressure switch(side of accumulator) directly to the ecm. everything will work at that point
    Michael Bray
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  11. #11
    Senior Tuner mbray01's Avatar
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    that a12 circuit needs to go to ecm, not hvac module for it to work
    Michael Bray
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  12. #12
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    I currently have pin 55 grounded. But still says it is not receiving serial 2 command to turn on. Are you useing the 2 pin high pressure switch or 3 pin?

  13. #13
    Senior Tuner mbray01's Avatar
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    IF YOUR USING THE VAN OPERATING SYSTEM, THEN THE ECM DOES NOT LOOK FOR A CLASS 2 SIGNAL, THAT IS ONLY ON THE TRUCKS. THE VAN GETS ITS ITS A/C REQUEST SIGNAL VIA THE HIGH PRESSURE SWITCH(back of compressor) to pin connector 2 pin 17
    Michael Bray
    Rusty Knuckle Garage
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