This could be due to a faulty blower motor resistor. Many times when these resistors go bad it will only allow one speed of fan.
The resistor is located under the passenger side dash.
I have attached diagrams below for your reference, also included the test procedure for the resistor.
Let me know of any questions.
Images (Click to enlarge)
Friday, July 1st, 2022 AT 3:58 PM