fan control speed only works on high

Bad blower motor resistor (aka 'thermosistor'). The resistor pack sits on top of the blower motor itself, it decreases the voltage that reaches the motor based on your speed selection. At high, full voltage is applied to the motor (bypassing the resistors) which is why it works on the high setting and not the lower settings. It's about a $30 part, and is easy to swap out, by dropping the glovebox door all the way and reaching up to the blower motor, detaching the wiring harness, and unscrewing the resistor pack and popping in the new one.