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?
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.
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