Originally Posted by -AL-
I'd look at is the Resistor switch(not sure if thats its correct name).
Under the Glove compartment screwed into the heater box. Small plastic thing with 2 or 3 coils & like a relay/switch thing.
Symptons include fan will run o.k on highest speed but not on the others.
i suggest trying this first and this will help you determine if it is the resisters or actually the motor.
actually i have found that more chevy's have this bad resister setup than fords but it should be the first thing to check.
if the motor does not run at all in any position of the switch then try moving the wires around and see if the connector is loose.
after that pull apart the connector and check the voltage inside on high the voltage should be the same as the battery and obviously less with each lower setting.
if this is found to be true then at this point the motor itself will need to be replaced.