I have a 2005 Mercury Montego Premier. Can I change the clutch hub only on my ac

yes you can replace the clutch but it is tricky doing it because you have to have the right gap in the clutch to make it work properly plus you will need a puller and installer kit to re & re clutch

I had a similar problem. Had vortex tube and dryer replaced. Then the compressor had fluctuating pressure as car would only stay cool above 1200 RPM. Had to have compressor changed.