[SpinnerCee]

In addition to the HVAC [1-5] fan control dash switch, there's a relay that applies full power for the higher fan speeds -- the relay may be stuck closed such that the variable control can no longer turn the blower off.

The blower motor speed control resistor pack may also be shorted out -- The blower motor, resistor module, and relay are all located under and behind the glovebox -- to get to them, you need to drop the blower motor -- it's really easy, 3 screws -- you can probably replace the module and relay yourself. Since you can't tell if they're bad by just looking at them (unless they look like they've been under water) -- you may just have to buy the parts and save the labor for yourself.

The problem may also be in the fan speed switch itself -- some WD-40 to the contacts under the speed control knob has fixed this for some.