The belt tensioner’s main job is to keep the serpentine belt tight. Most late model engines have an automatic tensioner that does it. Over the course of its use, most car owners tend to forget about it and just change the serpentine belt instead. The tensioner features an automatic spring-loaded that most definitely wears itself out, although not as fast as the belt itself. Failing to replace the belt tensioner will guarantee a never ending cycle of serpentine belt replacement, the AC compressor relies on the tensioner as it goes through the on/off cycles.
