1995 GMC 2500 Pickup Q&A

1995 GMC 2500 Pickup Question: what could cause the belt to jump off the pulley?

My belt keeps jumping off the pulley. I thought it was becuase of the air conditioner pulley so I got a new one. I also got a new belt. I dont know what else to do. -
Answer 1
usually its your idler or tensioner pulley that causes this problem -