Your home air conditioner is like any other piece of equipment that pushes air, such as your furnace; it has a filter that needs to be attended to. In most cases, the air conditioner filter is at the front of wall-mounted or window-mounted units. Those filters do not need to be replaced. They do need to be cleaned once a year. The best time to clean them is when you are done using them for the year, and before you put them into storage. Central air conditioner units take removable filters, and those should be replaced at least once every year.