1998 Buick Regal, Any ideas why the A/C fan only runs on the high setting?

1998 Buick Regal, Any ideas why the A/C fan only runs on the high setting?

Sounds like you have a defective blower motor resistor. Its located in the blower motor and housing assembly under the passenger side of the dash board.

I had the problem where the fan would only run for 10 second then off for 30 and on for 10 and so on and so on. found out it was a poor battery problem.