A/C blower control low fan speed stopped working

Hello,

It sounds like an issue with the blower motor resistor.
That resistor can go bad and will only come on in certain speed setting.
This truck also has a blower motor speed control unit which can also trigger similar issues.
But the resistor should be checked first.

To access the resistor you will have to remove the panel below the glovebox on the passenger side.

Here is a helpful video:

https://youtu.be/VI9x3rUKVBo

I have attached diagrams for your reference

Please let me know of any questions.
Thank you.