A/C noise

I recently had my 1984 buick century retrofitted to the new ac type but now whenever i accelerate and the car sounds like its shifting gears. I get a really loud squealing noise now im not sure if its the pulley or if its the band that is slipping or what it is. but if anyone has any ideas on what i can do to stop the noise or if you can tell me if im hurting the car please let me know. Note: it only does it when the ac is turned on, when i turn it off there is no noise.