Air con switch works on slow speed only - 2000 Ford Taurus

Side from the air conditioner controls, your resister stack maybe is bad... this is the part that controls how strong should work the a/c at each speed. that is a easy fix. The blower motor resistor is usually located on the passenger side, under the dash.

You need to remove the closeout panel, under the glove box. Look up in there and you will see the blower motor, and just over and off to the left you will see the blower motor resistor.

here is some steps in how to change it: http://www.ehow.com/how_4760922_change-blower-motor-resistor.html

here is some pic showing were: http://z.about.com/d/autorepair/1/0/H/K/41748830.gif