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How to Maintain an Air Conditioner

Ask This Old House plumbing and heating expert Richard Trethewey shares tips for keeping an air conditioner running efficiently


  1. If your air conditioner never shuts off, it may not be running as efficiently as it can be.
  2. Ensure the outside condenser is debris free. Use a vacuum cleaner with a brush attachment to keep the fins clear of dust, pollen, pet hair, or other contaminants.
  3. Periodically change the filter on the indoor air conditioning system. Use the existing one as a guide to purchase the correct size and follow the “flow” arrow when reinstalling.

The shop vacuum, brush accessory and HVAC air filter shown can be found at the local home center.