A dirty air conditioner filter decreases your system's efficiency and increases the cost to run it. Remove the old filter, take note of the size, and purchase a bulk package from your local home improvement center. Aim to change the filter at least every four to eight weeks.

Josh Armstrong /Staff/File
air conditioning window units dot an apartment building in Boston in this 2005 file photo. Changing out your air conditioner's filter every four to eight weeks will help it run more efficiently .