AC Inspection Guide | DIY Air Conditioning Check-Up

You don’t have to be Sherlock Holmes to figure out if you have an air conditioning problem. All it takes is some common household items and knowledge of what to look for and where.

For the most efficient and cost-effective air-conditioning, it’s highly recommended you schedule professional maintenance in the early spring. But that’s not all. You should also be replacing the air filter every 30-60 days and conducting some DIY maintenance and troubleshooting of your own.

Use this AC inspection guide to check the status of your air conditioner at least twice a year—once in the beginning of the cooling season and again toward the end.

DIY Air Conditioning Check-Up

Warning: Always turn off power at the source (breaker box) before inspecting, cleaning, or poking around any HVAC components. This includes changing air filters, cleaning condenser coils, opening access panels, and cleaning vents and registers.

Here are the materials you’ll need:

  • Flashlight
  • Screwdriver
  • Toilet paper
  • Piece of twine or yarn
  • Pen and paper


  • Check for good airflow by holding a 1-foot piece of yarn in front of each supply vent. If the yarn or twine flutters and goes nearly horizontal, you have enough airflow.
  • Test for proper air draw from return vents by holding up a tissue or piece of toilet paper. The tissue should be sucked right against the grilles and stay there.
  • Make sure all of the HVAC vents and registers are completely opened and unobstructed.

Although many vents come with louvers to adjust the airflow, it’s best to keep them all the way open, all the time. This allows your duct system, which has been specifically designed for your building, to flow freely. Closing or blocking HVAC vents can restrict airflow and cause pressure buildup leading to duct leaks.

Facilitate airflow throughout your home by remembering to:

  • Frequently vacuum and dust around supply and return registers.
  • Check the air filter monthly and clean or replace when it looks dirty. Learn more air filtration tips.
  • Keep all supplies and returns open and unobstructed so air can flow without impediment.
  • Don’t leave interior doors closed for extended periods of time. Keep the air moving.

Indoor Air Handler

Now that all of your return and supply vents are open, clean and clear, it’s time to head to the indoor air handler.

  • The indoor air handler access panel (cover) should always be on when the system is operating. If the cover is off or damaged, contact a pro for service.
  • Listen for any strange sounds, such as screeching, squealing, whistling, or hissing. Whistling and hissing can indicate an ill-fitting blower compartment. Hissing can also come from a refrigerant leak. Squealing can mean an issue with the fan belt and blower. Buzzing can indicate electrical problems, loose, or malfunctioning parts.
  • Before you investigate any further, shut off electricity to the system.
  • Locate the furnace and make sure the cover is properly fastened. You don’t want any dirt, dust and debris entering the blower compartment.
  • If readjusting the cover to the blower compartment does not stop the strange sound, contact a professional.
  • Pay attention to strange smells as well. Learn why your air conditioner might smell bad.

Air Filter

Clean air filters are crucial to the performance of your air conditioner and the quality of your indoor air. First, you need to know where the air filter is located.

Your air filter could be inside the indoor air handler or behind one or more return grilles. Keep in mind that many homes have multiple air filters. Check both places. You may have a filter in both locations.

Once you have located your filter, check to see if it is clean.

When replacing your air filter:

  • Have a plastic bag large enough to hold the dirty air filter on hand.
  • The replacement filter is ready, the right MERV rating, and the correct size. Learn how to choose the best air filter.
  • Carefully remove the old filter and place it in the plastic bag without shaking in. Tie or tape the bag closed and take it to an outside trashcan or dumpster.
  • Vacuum and wipe around the filter area and surrounding equipment.
  • Follow the directions on the new filter’s packaging. Match the direction of the arrows printed on the filter with the direction of airflow.

If you have a washable filter, clean it once a month. Follow manufacturer directions. Usually, they should be washed with detergent water and a gentle brush. Before reinstalling the washable filter, make sure it is completely dry.

When inserting any HVAC air filter, make sure the arrows printed on the filter are pointing in the direction of the airflow.


While you are inspecting and possibly replacing the air filter, take the time inspect some other important system components.

  • Make sure power to the AC is turned off.
  • Remove the cover to the blower compartment.
  • Look at the blades on the blower with a flashlight. They should be pretty clean. If not, contact a professional.

Air Duct Leaks

According to Energy Star, “about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.” If the seams of the ducts are not properly sealed, you are losing a lot of energy and allowing contaminants to enter the air supply. It’s important to find and seal duct leaks for the benefit of your health and energy costs.

  • Turn the AC back on. Let it run for 5-10 minutes.
  • Use a thin piece of toilet paper to test for air leaks around duct seams and connections. If the paper moves around or adheres to the ducts, you have an air leak.
  • Look for more signs of ductwork problems.

Your air ducts should also be insulated. Learn about our Pure Flow Duct System.

If you notice any loose seams, do NOT use duct tape—the name is misleading. Instead, contact a professional for comprehensive duct sealing or seal the loose duct connections you can reach with mastic sealant or aluminum foil tape.

A properly maintained air conditioner will last longer, cost less, cool more effectively, and improve the quality of your indoor air.

Service Champions is known for trustworthy, on-time heating and air conditioning service throughout the East Bay, South Bay, and Sacramento areas.

If you have any questions or concerns, don’t hesitate to Contact the Champions.

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