You can visually inspect the belt (look for any cracks or abnormal wear) to determine where it's at, but the idlers and pulleys can be done one of a couple ways....I'd recommend just pulling the belts and giving each piece a spin. If you hear any growling, clicking, or feel any play/roughness I'd highly recommend changing the piece out.

You can also cheat and use a mechanics stethoscope if you have one handy. It'll save you the hassle of having to pull the belts as you can listen while the vehicle is running....but I advise against this method for obvious safety reasons.

__________________