It doesn't take long for washable air conditioner filters to get all dusty and grimy. Some folks just run them under water and put them back, but that doesn't really clean them. Because these filters are the perfect place for allergens and dangerous bacteria to collect and grow, it's important to really clean them two or three times each month.
Turn off the electricity to the air conditioner.
Remove the cover. Depending on the type of air conditioner, the cover may be kept in place with screws or with locking push tabs.
Slide out or unclip the filter from the unit and vacuum off any buildup of dirt. It will be impossible to get it all off -- just get as much off as possible.
Mix a solution of 1/2 vinegar and 1/2 water in a container or tub large enough to submerge the filter. The vinegar will remove allergens and harmful bacteria that have collected on the filter ... water alone can't do this.
Submerge the filter in the cleaning solution and allow it to soak for about an hour if you clean the filter often. If the filter is particularly dirty, allow it to soak for several hours.
Lift the filter out of the liquid and allow to drain. Do not rinse, but allow to dry as is. When thoroughly dry, return it to its place and put the cover back on.