2000 Chevy Malibu AC switches on and off

When using AC the, AC will go on and off randomly. The blower will stay on, but the green AC light will go on and off constantly, and besides not having AC, this causes rough idles if it is going on and off at a red light. If I mess with the switch, like turning it between numbers, or switching back and fourth, the AC will come on and off, almost like there is a short or something. The dealer replaced that whole part 2 years ago, and it worked fine for a few months, then went back to the same thing. I have not taken it back. It seems to be worse the more humid it is. Thanks for any suggestions.