Maybe late, I am still working on my project and still needing to address this. Fans on with compressor is not an option for me. Modern vehicles do not do that.
Found this informative thread from some time ago
https://lateral-g.net/forums/showthread.php?t=40215 It is lengthy, so a long read. A lot of good info. From what I read there is zero reason to turn fans on with compressor.
Gives me hope that I can use the pwm fan control with its advantages from my e67 ecm.
Edit- maybe should have pointed out there is info on installing a stock gm pressure switch and connection to ecm. If you want stock type fan and a/c operation the thread is a good read if you can get though it.