What could most likely be the problem with my ac? on 2003 Oldsmobile Alero

It blows cooler on outer vents but only blows cooler air for a few seconds. Only the top two blower switches work on high and higher. Just went out its been extremely hot 100+ past two months. It used to vibrate real bad when in park and ac on now when in park and ac on it doesnt vibratr at all. And seems to have more power maybe. Help!

Asked by for the 2003 Oldsmobile Alero
poss balance issue on blower fan and poss blower motor resister going out