What are the dynamics behind the HVAC blower motor speed control, on a 2001 Nissan Sentra?

A good many months ago, the blower ceased to operate in this vehicle, unless the blower motor speed control switch was in its highest position, i.e., #4. Initially, it operated normally in this position. Now, blower output is weak and labored. My thoughts are, the switch is a solid state device wholly... show more A good many months ago, the blower ceased to operate in this vehicle, unless the blower motor speed control switch was in its highest position, i.e., #4. Initially, it operated normally in this position. Now, blower output is weak and labored. My thoughts are, the switch is a solid state device wholly responsible for speed control, i.e., the blower motor is not a multi-speed motor.
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