How do I change loosen the fan belt on a 1988 Cherokee 4.0 liter I back off the adjuster bolt but the belt stays tight?

If your vehicle has an automatic belt tensioner with a serpentine belt, the belt is worn and needs to be replaced. On older models, the belt tension can be set by adjusting it at the alternator bracket. Loosen but do not remove the two bolts that hold the alternator in place (one at the bracket and one on the block) and pull the alternator to tighten the belt. Hold in position while re-tightening the bracket bolt then tighten the bolt on the block.