My a/c only works on speed 4 of 4, changed speed switch still same what else.

Your problem is the blower motor resistor. That is what needs replaced.

Don't know your skill level but here goes, these are the parts you need (NAPA numbers) ECH-BR285 and EC1285 this is for the blower resistor and the connector. Located behind glove box, left of the blower motor!! Save yourself some trouble, if the connector is burnt at all replace it also!!!

blower motor resistor is bad. under dash pass side