2005 Chrysler 300 Alternator Problems

Air Conditioning problem
2005 Chrysler 300 6 cyl Automatic 120000 miles

Recently our car started losing its charge and we frequently had to get jumps. A diagnostic test from the parts store showed that the problem was our alternator. We changed the alternator and since then have had worse problems. The car now keeps a charge but it makes a loud screeching noise when in use and if you turn on the air conditioner it locks up the power steering and puts strain on the belt. We have also put a new battery and new belt on the car since then and are still having the same problem. Also the battery light comes on now when we are driving, which it did not do before the new alternator. What could be causing these problems?