On an a/c system, the water pump pulley isn't very big at all and has to be run with a specific idler pulley and a bracket that mounts to the water pump too.So the water pump has it's own belt that is driven off the crank and idler. Then you have a pair of belts running the a/c compressor and alt. Then a seperate belt for the power steering I do believe. Totaling 4 belts with 2 being a matched pair for the a/c.