Here is what my book says:
Blower Motor Speed Control To Remove:

1. Remove the right lower instrument panel insulator.
2. Disconnect the electrical connector from the blower motor speed control.
3. Remove the blower motor speed control mounting screws.
4. Remove the blower motor speed control.

Sound like your blower resistor is bad if it works on HI and nothing else...you can find that behind the glove box on the heater/a/c assembly, near the motor....hope this helped...GL