Someone has jerried the wires and eliminated the high sw.
They have probably used a temp sw that just uses the single wire from the relay and grounds it. Ground that wire and see if you get low fan..My guess is they did not want to open the system up to change the sw , so they did away with it [ they may not have even known that the refrigerant level was probaly the cause to begin with ..]
I also think the high fan you are seeing is b/c you have modified the coolant sensor to lower cut-in and that has nothing to do w/ac fan..
Do you have low fan w/jumper ????