How to Clean Central Heating & Air Conditioner Evaporator Coils

Keep air flowing properly through vents with regular evaporator-coil cleaning.
Keep air flowing properly through vents with regular evaporator-coil cleaning. (Image: air conditioner vent image by Tammy Mobley from

The evaporator coil, also commonly referred to as the A-coil because of its shape, conditions the air before it flows throughout the home. Since the air must pass through the coil, it is susceptible to the accumulation of dust or dirt that can hinder the performance of the furnace and air conditioner. A thorough cleaning is required to keep the appliance running at peak efficiency and homeowners have various options available to do just that.

Things You'll Need

  • Shop vacuum
  • Compressed air
  • Aviation snips
  • Screwdriver
  • Metal screws

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Disconnect all power to the furnace and air conditioner. (See Reference 1.)

Open the access door on the plenum to allow for cleaning with a small shop vacuum. If no access door is present, one can be cut to allow access to above the coil and below. Be very careful not to damage the coil or tubing in the process. Any puncture in the tubing and the refrigerant will pour out. This damages the ozone and is costly to have someone recharge the system after they replace the tubing. (See Reference 1.)

Clean the coil with compressed air or steam in conjunction with a powerful shop vacuum. Place the vacuum on the dirty side and blow compressed air on the coil on the cleaner side, which is above the coil spraying down. If high pressure is used then be careful that you spray the coil straight at the fins or on a right angle to prevent damage to the coil. (See Reference 1.)

Inspect the coil for any signs of bent fins. If a couple are slightly bent, a coil comb can be used to move them back into position without causing damage. (See Reference 1.)

Spray a chemical cleaner from above the coil and allow time for it to clean the coil further. The duration and exact process can vary depending on which chemical product is used, so be careful to read the entire set of instructions and follow them precisely. Remove the dirt and chemical solution according to the instructions if removal is required. (See Reference 1.)

Reattach the access door or place a piece of sheet metal over the newly-cut access that is two inches larger than the hole. Secure it to the plenum with metal screws and turn the power back on. (See Reference 1.)

Tips & Warnings

  • Cutting into the plenum is not always easy and serious damage to the equipment and environment are possible if done incorrectly. The hole must be cut a minimum of three inches from any side, top or bottom on the plenum section. If easy access is not available, it is advisable to contact an HVAC specialist to perform the work. They may decide the best method is the removal of the refrigerant and then the coil for a more efficient cleaning outdoors.


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