a/c system on 2002 GMC Sierra 1500 HD

when i get off the throttle the a/c belt vibrates really hard, and it allready broke one a/c belt tenchioner

1 answer
a) I'd start looking at the AC compressor. If like my truck that belt only drives the AC therefore if your not running the AC & (b) you have a good belt (AC off) everything is smooth? yes - Go back up to (a) no- Go to (b)