You may let your window air-conditioner unit just run and run, keeping you cool, but you add to its work burden when you don't regularly clean its air filter. If you wait too long to clean the filter, the efficiency of the unit goes down dramatically and you are breathing air that has passed through dust. Clean the filters of units that run with fans at least monthly.
Turn off the window unit. Vacuum the front cover before removing it if it is dusty and grimy.
Remove the cover from the front of the unit, unscrewing its screws or pressing its push tabs to get to the filter. Note any tabs or cutouts to so you can correctly align the cleaned filter. Grasp the filter by its center and pull it outward.
Clean the filter at the same time as the front of the unit, in a sink if these items are not too big, or outside otherwise. Place the cover and filter in a pan of warm water containing dishwashing liquid or just hose off with a fine firm mist.
Shake the filter gently to remove excess water. Let the cover and filter dry completely and replace.