I am having an issue with the AC pressure signal in my LS swapped vehicle and have run out of ideas to test. I'd love any thoughts you may have:

  • I am running an E38 ECM and have added the AC 5V Ref, Ground, and Pressure Signal.
  • I am recreating the AC pressure signal with a simple voltage divider, creating ~2.0V pressure signal (my vehicle has a separate pressure switch to turn off the compressor, as needed).
  • This worked for a while, I could read the AC pressure in HPTuners and engage the clutch, but it has since stopped. I have been troubleshooting other elements, most notably working on a CANbus gateway with Arduino, but am not sure this would impact the pressure signal.
  • I can verify the 5V ref, the 2.0V pressure signal, and the ground signal. I also replaced the terminal connectors, just in case it was corrosion causing the issues.


I do not see any settings in HP Tuners that would impact the pressure signal. My only other idea is that the ECM is interpreting the steady pressure signal as a fault (and setting the pressure to 0 to keep the AC Clutch from engaging). However, that seems a bit unlikely.

Any other ideas?