Looks like the electrical part of the Mode Selector switch is shorted out. Looking at the schematics, the light green wire goes to the A/C select in the Control Module. I disconnected it and the compressor stopped running. Now I just need to add a switch so I can make it run when I want / need it to!
Attaching a pic in case someone is chasing the same issue later... can barely see the red oval I made around the A/C control connector on the right. On that connector there's a black wire in the bottom position that provides constant ground (basically for the entire HVAC control system), dark green wire in the middle (red in my pic) that provides switched ground to the controls (e.g. fan doesn't run if the Mode Selector is in the Off position), and light green in the top position (white in my pic) that goes to the A/C select as stated above. Sorry about the wire color confusion, I had to chop out wire w/ melted insulation and used different colors.
One step closer. Still only have high speed working and some sort of ground feedback issue causing the relay to not shut off when the resistor is connected. Next step is probably going to be to run new wire from the fan switch to the relay as I suspect the wires are shorted.