Ok, the most common cause is the blower motor resistor, located behind the glove box- see attachment, but may be the blower switch or melted wiring at the resistor connector
Disconnect the the harness connector and inspect it for signs of melting and replace connector if found.
If ok, at the resistor itself, with an ohmmeter, check resisance between each of the terminals and if missing from between any two, replace the resistor.
If both wiring and resistor are good, then replace the climate control panel with blower switch
9 times out of ten it is the resistor
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