0411 To P59 Swap AC Request Not Working

[lownslo93]

Swapped a 0411 with AC working to a 12586243 PCM with OS 12592618. I switched the AC type to analog cycling and the AC relay will not engage from the ECM. I can get AC requested to show yes, and I can engage the relay from the controls window. I tried adding an 80k ohm resistor to fake out the pressure sensor and it will read 2.14 volts and still not engage. If I switch to serial or serial cycling it will engage the compressor, but I don't get any cycling out of it. I can unplug the high and low pressure sensors and it will stay running. Do I need to re-wire these? I have thought about getting just a low pressure switch connector and wire it inline with the resistor as an option for a quick work around since it does nothing currently unplugged.

If I flash it as analog only it will sometimes will engage the compressor but in the same boat where it just leaves the compressor kicked in all the time with no safety. Has anyone had luck with the 243 ECM working with an analog request before? Or do I need to look at a different service number? I have tried about every suggestion I've read on multiple forums and have not had the same luck as others or am I doing something wrong?

This is on a 99 GMC K3500 OBS with the 7.4 vortec. Any help appreciated.

6-4-22 - DFCO ON ATTEMPT.hpt
6-9-22 AC Log.hpl

[lownslo93]

*Update* Think I found a solution to this beast. I was able to get it to engage on Serial Cycling with a 150K ohm resistor wired into the AC pressure sensor. So I had the idea to get a low pressure switch pigtail and wire the resistor inline to that to make it cycle on/off. That didn't work, as when the switch would cycle or to test it unplug the sensor it would cut out the compressor but would not re-engage when plugged back in. I had to power cycle the ECM to get it to engage again. So I used post 5 out of the link below to reroute the AC request 12 V input through the new pigtail to the low pressure switch and keep the resistor wired in all the time. Now it works well and will cycle correctly. Just need to clean up some wiring and happy trails.

https://ls1tech.com/forums/pcm-diagn...green-pcm.html