It is possible to get around 12 volts, but with amperage so low, unable
to turn the motor. I betcha 32 cents it's the Blower Motor Relay -
chances are the contacts are so pitted with age and use they are no
longer able to pass the amperage required to to spin the Blower Motor.
This link applies to Dodge Caravans, but I am sure the concept applies
to most vehicles...