The fan (heating, AC, etc.) on my 2003 has stopped working in positions 1, 2, and 3. To get any air movement in the car I have to go to 4 or 5. Is there a specific fuse that pertains just to fan speeds 1, 2, and 3?

Common problem.

1 - the switch itself

2 - the voltage dropping resistors ( coils ) I don't recall if these are located near the switch or located near the blower assembly.