Doc here,

imp:
I'm Not sure the blower switch needs to be changed..It will operate the same (speedwise and on/off) with or without AC...
Where the changes might come in , is the vent door (if electrical) on the control head for opening and closing the vent doors, and activating the AC Clutch. These CAN be mechanical, (cables) , or Electrical (micro switches) , or Vacuum operated.
IIRC, all the wire for AC should be in the Harness already..but not sure about that..I think they ran them as spares in a Non AC unit so they wouldn't have to discriminate between Non and AC harness on the line..(one fits all) so compare between the two and see.
Doc

imp: