'taint gonna turn off all the way. To keep the pressure inside the cab from getting too high, the blower motor is designed to always be on.
As far as not being able to adjust the speed of the motor, your switch may be bad.
SgtDel
aka "Andy"
www.delbridge.net
1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4