Switch only works on high fan speed?

your problem sounds like it is the blower motor resistor, its located right beside the blower motor and its held in by 3 5.5mm screws. the circuit board on it will be burnt out, its very common and i think the new ones are updated so they don't keep burning out. i replace these at least on a weekly basis. Here is how to change the switch out and the resistor to help fix the problem. Check out the images (below). Please let us know what happens.