A/C blower control not working

You are correct that this is most likely a blower control issue but we need to start with this guide to figure out what the issue is:

https://www.2carpros.com/articles/low-or-no-air-flow-from-vents

I suspect that this is the fan amplifier so we need to test voltage on the red wire and the blue wire from the amp and see if it is changing when changing the speed. If not, then the control panel is the issue. If it is then the amp is the issue.

I attached the info below on this. Let us know if you have questions and we can go from there. Here is a guide that will help with this testing:

https://www.2carpros.com/articles/how-to-check-wiring

Thanks