1997 Cadillac STS oil light

Hi just bought 97 sts and did not notice right away but at idle(red lights) the little oil can light flickers?Pls tell me it could be some type of sencer or pressure switch. If not what do I do to figure out problum?Seems like raising the idle speed would fix but it idles at about 750?I that cars normally idle closer to 1000-1100. Also the a/c works fine but once in awhile it switches from dash vents to defrst or floor for a couple minutes and then goes back?The back a/c vents are not affected?