You were advised in beginning about checking the ground points. You have the service manuals , the ground point locations are ALL shown in the descriptions and in cutaway diagrams. It's your choice to guess and randomly change parts, success eventually.A breakthough, I got a piece of long copper wire and I touched it to the negative terminal on the battery, I then brought the other end of the piece of wire and I pressed it into the relay socket on the pin that's supposed to be ground while the relay was installed into the socket and the A/C Compressor turned on. So I guess it's time to check out the wiring or wherever that ground is.
Did you ever open the service manual?