The high pressure switch turns on the radiator fans to high speed. I don't think it would override the a/c controls in the dash. Do you have a Ford service cd, they have them on e-bay, or go to
www.alldatadiy.com and sign up for online manuals, you need the schematics. You could try disconnecting the mode switch, and see if the a/c will then stop, if it does switch likely bad. There is a hidden screw on the bottom of the radio dash trim if you try to disassemble.
