Chevy S10 AC\Heater blower motor on 2000 Chevrolet S10

Why would my AC\Heater blower motor continue to run after shutting off engine and removing key from ignition. It will also operate intermittedly on\off at random while driving down the road? When vehicle is off and blower is running, the speed of the fan cannot be changed by the fan speed switch i.e. the speed stays at a constant rate of whatever it was set at when vehicle is shut down.

Asked by for the 2000 Chevrolet S10
blower resistor shorted to power. it is by the blower motor in the heater case.

1 more answer , 1 more comment
are you you sure its the a/c and heater fan?the reason i ask is the a vehicle with a electric cooling fan not a belt driven fan will contue to run till the engine temp drops this fan if electric will also kick on even if the has not been run in awhile due to the abient temp reached a certian degree.
yep it's the blower. it has a clutch fan system for radiator cooling. thanks for the feedback though.