I believe you have to add a wire, sensor and adjust the setting in your pcm for it to function like that. There is some good information in this thread, long but troves of information. Maybe John Parsons (ParsonsJ) can add something to this. I remember reading a while back that he added it to a customer's car.
https://lateral-g.net/forums/show...t=John+pwm+fan
Are you running a GMPP harness? The GMPP setup only has one fan output. I bought a kit from PCMofNc that adds another relay/output to the GMPP relay center. I never used it and ended up using the Entropy system. If you are interested in that thing let me know.
I also have the same issue with the idle rpm drop with AC on. Will be watching this thread.