I got a strange one for me... AC switch works on high and all other speeds blow low, but they blow. I replaced the resistor with Motor Craft, blower switch replaced behind the climate control center. New compressor, new dryer, new orifice tube. What could be causing this? 2002 F350 7.3 4x4. I have a valve that shuts off the supply to my heater core as well. I can't figure out what else could be controlling the blower speed. Any ideas or help will be appreciated.