1996 Nissan Altima AIR CON ONLY WORKS ON HIGH

Air Conditioning problem
1996 Nissan Altima 4 cyl Automatic 208720 miles

My AC works only in the highest level, and it works great for about 20 minutes then it just blows air. Should I just recharge the AC? Or is something else wrong with the AC, maybe something wrong with the AC line? Thank you.