Chevrolet Repair: a/c problem, chevy z71, bump in the road

Question
I have a 1993 chevy z71 5.7L. It has a serpontene belt. When i turn my a/c on the belt starts jumping in one spot.. If i hit a bump in the road the belt will jump off. I can hit bumps in the road all day long with the a/c off and no worries. The belt doesnt jump except when the a/c is on. What do u think causes that?

Answer
HI JOHN, THE A/C COMPRESSOR IS LOCKING UP, OR IF YOU RECENTLY HAD THE SYSTEM CHARGED IT IS OVERCHARGED. VERY RARE BECUASE THERE IS A HIGH SIDE BLEED VALVE IN THE COMPRESSOR TO RELEASE FREON IF THIS HAPPENS.. THE A/C COMPRESSOR IS CAUSING THE BELT TO OVERLOAD ITSELF...THIS IS A LONG SHOT BUT,, IN SOME CASES THE BELT TENSIONER COULD BE GETTING WEAK CAUSING THIS. TRY TO MOVE THE TENSIONER WITH A WRENCH IF THERE IS ALOT OF TENSION THEN MORE THEN LIKELY IT IS OK.. I HOPE THIS HELPS YOU,,, TOM..