A/C Heater Blower switch

The dash mounter switch on 2000 Focus has been giving me problems for some time. Until recently the only speed that worked was high--slower blower speeds did not work. Today, the high speed gave out--could
smell something burning. I replaced the resistor behind the glove compartment with no effect. How can I replace the switch, or must I take to a dealer?
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It's probably not the switch. The resistor pack you replaced has a thermal diode in it that blows like a fuse when it gets too hot (>220 degrees F) because of lack of airflow due to the blower motor not turning.
I would remove the pack and test the diode with a meter (it will only pass current in one direction if good; if bad, it will read open when checked in both directions). If it's bad, remove the blower motor and check that it still works when you connect it to a 12V source.
If the pack tests good, then after checking the blower fuse, check the leads to the resistor pack for corrosion and/or shorts. You can then check the 3-prong lead to the pack for voltage for each of the 3 fan switch positions. If you get nothing, then the fan switch is bad.
Bob
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