The switch that runs the blower motor for air and heat sends the DC voltage through some big resisters when it isn't set on high. (On high it sends all the power to the motor.)
If the lowest speed doesn't work then one of the resisters has gone bad, or come disconnected. If more than 1 speed doesn't work then a differant resister has gone bad or disconnected. The power runs through each resister in series so the most common one to go bad is the second to highest speed. when this resister is bad thaen it will only work on the highest setting. Replacing the switch won't fix it. You will have to find the resister that is bad and replace it.
The resister bank is usually tucked up behind the dash where only a kid can focus his eyes, and contort himself enough to see it.
Once the resister is replaced it should run perfectly.
Presto.
Cost $186 to get this fixed by dealer. Plus the labor......!!
There is a resistor that drops down the voltage for the blower motor to control the speeds, sort of like a potentiometer. Try replacing that unit, its usually under the passenger side fo the dash near the air box
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