I found on another site how I can solder a jumper on the control board. I did this and at least the AC comes on when I press the button. It lacks the pressure I would want and will have to dump some refrigerant into it, but that is life. Bigger fish to fry on this thing
I am having the exact same problem with my 83 FJ60. I took out switch and tested, jumped compressor to battery and it works, voltage at compressor plug jumping around at low voltage. What ended up being the solution for you?