Heater blower only works on high

Assume all of this is related, the most likely cause is the HVAC control module in the dash. It controls all the air doors and blower motor.

The way we need to figure this out is hooking a scan tool to the vehicle for two reasons. First check for codes.

Second, we need to try and command the doors to different positions and change the speed of the fan. If we can do all that with a scan tool then we know the control module is at fault because the scan tool will take place of the module in doing these things. Then we also know that they are capable of doing it, they are just not being told to do it which points to the control module again.

Most don't have a scan tool that can do this so let me know if there are codes and hopefully we can come to this conclusion a different way. Thanks