> but anything after that (2-3-4) and the green A/C light turns off by itself.
Does the fan still work on 2-3-4? My first guess is that it is a bad fan speed selector switch.
99% of the time if it is a blower motor resistor pack you will have high-speed (4), but not 1-2-3. So it doesn't sound like a blower motor resistor pack issue.