Why is my car dying out & rpm gauge going crazy when I turn on the AC?

2000 Pontiac Grand Am, 6 cylinder, 130 K. Whenever I turn on the AC the car will act like its going to die at first, then a few seconds later, die out. During this time, the rpm gauge is going CRAZY! Moving up and down, up and down. This week I have been to the same shop 3 times. All failures! I have gotten a new alternator, battery, pcv valve and pcv valve hose, tune up and my throttle body cleaned. No luck! There is no check engine light on. All this money spent and I have gone no where! Still have the same problem. Someone please help!