I have a 2002 Dodge Ram 1500. My ac only works on high and it squeals.

Possibly blower resistor AND blower motor problem.

Most certainly a blower motor resistor. There is a good chance you'll have to replace the blower motor as well. At the very least you need to measure the amperage draw of the motor circuit while its running. If it is too high you need to replace it or remove it and see if there is something stuck in the cage causing it to bind up.