This should be done every year, whether you have window or central units. Check your air conditioner s filter every time you receive your utility bill. Look for a dust build-up that can restrict the airflow and place stress on the system. This added stress places wear and tear on the unit, and increases operation costs. Filters can be washable or disposable.
Most hardware stores carry inexpensive, fiberglass filters that are disposable.
Measure the existing filter or filter opening. You want to buy the proper fitting filter. If fitting is not correct, it will not filter the debris. It is best to keep several filters on hand. Always replace the filter cover.