Engine Cooling problem
1995 Toyota Tercel 4 cyl Two Wheel Drive Automatic 229000 miles

My car just started to overheat (gauge goes half way up but never redlined) and then white smoke or steam seems to come from the defroster vents. Since I live in Florida the air conditioner is running constantly. If I run the car without th a/c on it does better. I mean it takes longer for it to happen. Do I replace my water pump ? I had to refill the radiator half way the first time it happened, but I can't see any sign of my radiator leaking. Tonight I noticed a kind of shrill whine coming from thje engine but could'nt pinpoint where the noise is coming from. Help!