Blower fan motor only works on high?

Hello,

It sounds like you have a faulty blower motor resistor.
The blower motor resistor controls the speed of the fan after you turn the knob.
Over time the connectors for the resistor wears off and can only work in one setting or not work at all.
The blower motor resistor is located behind the dash panel on the center.
It is mounted to the blower motor.
That resistor can be replaced using simple hand tools in short period of time.

Here is a helpful video:

https://youtu.be/IoAdY2twhFI

I have attached diagrams for your reference.

Please let me know of any questions.

Thank you.