The blower motor started only working in high speed . Changed the resistor and harness pigtail, worked one night next morning same old story high speed. checked resistor and connections nothing. don't know what to check next also put a new speed switch on.the control panel

 

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It's possible that the blower motor bearings are worn and the motor won't start on the lower voltage settings. If that is true, a new blower motor would be the fix.