Pontiac Repair: GMC Yucon xl ac Tensioner bobbles, gmc yucon, streached

Question
QUESTION: My Question is why does My lower Belt Tensioner Bobble This goes Arond The drive shaft pulley And AC Pully only.

ANSWER: Hi David:

More then likely the spring in the tensioner os weak and making it move up and down. Or the belt is worn out "streached" and it's past what the normal amount of slack the tensione can take up or lastly the a/c  compressor is seizing up or the line pressures are to high in the a/c system. Does it do it when the a/c is on only? or all the time?


---------- FOLLOW-UP ----------

QUESTION: It bobbles only when the AC is on.

Answer
It can still be any of the 3 issues I mentioned before. Depending on what year this is there may or may not be a mark on the tensioner arm and on the tensioner body and they should line up meaning the belt is not streached and the tensione has the proper amount of pressure on the belt but Not all of them have those "witness" marks on them.