when a/c is on car won't go

I have a 1985 cutlass ciera brougham w/3.8l v6 engine and I'm having trouble getting the car to go when I make turns and sometimes even leaving from stop sign or traffic light when I have the a/c on. It just revs up like it would if car was in neutral, so I have to shut off air to get it to go. I know that running the a/c can take away some power from engine when it's on, but all of it?? I'm mystified by this as I've never had this problem with any other car before. At first I thought maybe transmission fluid is shifting to one side when I make turns causing it to not go, but that can't be because it's just fine with the air off and fluid level is perfect. Does anyone know what the problem may be??