More than likely the blower resistor is blown.
I'm not sure of the location on your car, It may be on the firewall near
the blower motor.
If it is there are 2-3 screws holding it in. Remove the srews and pull
it out. You'll see about 3-4 coils of wire, if you see one or more of
the wires broken, there's your problem.
1991 Pontiac Bonneville LE
3800 V6 ( C ), Black/Slate Grey
~~~The Former Fleet ~~~
89 Cavalier Z 24 convertible
78 Holiday 88 coupe
68 LeSabre convertible
73 Impala sedan