Where is the ECM in your diagram? You want the ECM to control the compressor so that the added load on the engine is compensated for by the ECM. Usually a/c request is straight to ECM (through HP cutout switch) and the ECM output (pin 43, ground output) goes through the relay. Fan request is via the ECM as well. Why do you need a trinary switch? If you want fans on when a/c compressor is on, then just wire the fans through another relay in series to the a/c compressor relay (a/c relay triggers fan relay).
Note: Your a/c on/off wire (from control panel) IS the a/c request wire.
https://lt1swap.com/99-02acwiring.gif