rear a/c belt

i have 2007 that is having issue with rear a/c compressor belt.belt started squeeking and did not appear to be running centered on idler pulley.got new belt and watched while running and the belt walks back and forth on idler pulley.it walks off the edge and back which cant be right.anyone seen this issue.

Make sure that the tensioner is adjusted for good tension on the belt. Also make sure that the tensioner pulley does not have an alignement issue. It should not be walking at all. You might have an issue with the AC clutch, but the belt should still not be walking.

Chris