Wiring AC compressor on '72 C-10 LS swap

[406Weiand142t56ina65]

No hurry on this…but let me know if you can give me some direction and better understanding if my plan is good on hooking up the AC on my ’72 C-10 FACTORY AIR gold/white truck with 2004 Tahoe 5.3 and ECM. I have already vacuumed down and charged the system with the appropriate amount of refrigerant.

Issue: wiring AC using factory C-10 AC demand switch, to activate LS engine AC compressor, cooling fan and heater control valve. I’ve looked online but it doesn’t seem any two people do it alike.

Objective: turn on factory dash AC “plunger type” switch, have the high/low pressure switch complete/control the circuit, have AC compressor & electric fan receive "turn on” via relays due to high amp load and VINTAGE AIR electric heater control valve to receive "activate" signals to close heater control valve… and also wondering if the PCM needs to be involved or controlling this for idle, etc purposes…as I was planning on NOT involving the ECM as that is where my confusion comes in.

Plan A:

Materials: Planning to use Single post 4 way power distribution block, two relays, four 14 gauge wire & inline fuses, 10 gauge for pins 30 & 87.

Wiring: power from factory AC dash switch (already confirmed good) to/thru high/low pressure combo switch, then to distribution block via inline fuse, split 3 ways there, all three fused inline... the 1st to supply first relay pin 86 for triggering AC clutch via 87, the 2nd supply wire to 2nd relay relay pin 86 for triggering electric fan via pin 87… and finally the 3rd wire to the heater control valve, no relay required. Of course, 10 gauge battery to pin 30, 10 gauge from pin 87 to cooling fan and AC clutch individually.

Plan B: Do most of the above but interrupt the circuit between high/low switch & distribution block (or before high/low switch) and send it to the ECM fuse box for the ECM to be aware of AC demand. I think it involves tying in different pins…maybe between the high/low combo pressure switch and running it thru two spots in the ECM so it can control circuit…but I’m cloudy on that and there seems to be a variety of opinions online.

Thanks much