Accessory drive belts should be inspected every time you open your hood. More often than not, belts start slipping before they snap. So run the engine at high rpm with the a/c compressor engaged (it produces a substantial load) and listen carefully. Also, check for belt wobble, which usually indicates a damaged pulley or adjuster.

To inspect a belt, turn it over at many points around its circumference. If you see glazed sidewalls, cracks or roughness on the underside of a conventional V-belt, it's history.

Occasional cracks in a ribbed belt are harmless, but if within any 3-inch section you see three or more cracks from the tip of any rib to the belt body itself, replace the belt. Also, replace a belt if there are any missing chunks of rib or a build-up of belt particles (from wear) between the ribs.

Before removing a serpentine belt, check the routing. Many vehicle makers have a belt routing diagram on an underhood decal. But if you've got a vehicle without one, make a drawing before you remove the belt.

Always clean the pulley grooves with a wire brush to remove any debris before you install a new belt. A belt that doesn't fit properly in the grooves will slip and shorter life will be the result.