fan speed switch will not function

Hello,

It sounds like the issue is with the blower motor resistor.
When you change the fan speed the resistor is what controls it.
Many times the resistor will malfunction, and you will only have certain speed.

The blower motor resistor is located in the blower motor housing. You will have access it from under the dash on the passenger side.

Here is a helpful video:

https://youtu.be/Be61A67ltP4

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.