Our database does not have any information on your vehicle so I do not know the exact design employed and what I have to say might not apply.
Check the crank pulley to see if it is equipped with harmonic damper. If yes, you could have a bad damper allowing the pulley to slip.
If AC and alternator shares the same serpentine belt, check the belt tension.
If everything test fine, have the alternator tested. It could be failing.
When AC is turned on, ensure the idling speed is correct and not too low.
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Monday, May 28th, 2012 AT 2:48 PM