1991 Toyota Truck install a belt to the air conditioner

It is very hard for us to tell you how tight to tighten the belt, as we just know from feel and experience. However, if you are determined to try, somewhere on the pulley is a tensioner just release the tension and remove the old belt. Install the new belt and tighten it so that there is approximately 1/2 inch of deflection on the longest span between pulleys. Recheck the tension after about 20 minutes running because after the belt breaks in, it may loosen up.