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Clean Evaporator Coils: How It's Done and How You'll Benefit

In air conditioning, heat transfer is the name of the game and clean evaporator coils are where it all happens. The less efficient the heat transfer process is, the longer the compressor cycles in the air conditioner must be to meet thermostat settings. Since the compressor is the primary energy consumer in a central A/C, longer “On” cycles mean higher operating costs and utility bills. Dirty coils alone can increase energy consumption by over 35 percent. It’s also often the root cause behind other dysfunctions such as coil icing and less effective humidity extraction. When diagnosing shortfalls in A/C performance and efficiency, checking for clean evaporator coils is one of the first steps.     

How Clean Evaporator Coils Get Dirty

Warmth in household air drawn over the cold surfaces of the evaporator coil is absorbed by refrigerant vapor circulating through the coil. Anything that comes between the transfer of heat energy in the air into the refrigerant inside the coil decreases efficiency of the cooling process. What could get in the way? Even a thin coating of dust on coil surfaces produces a measurable drop in heat absorbed by the refrigerant. Installed inside the air handler, directly in the path of circulating air, the evaporator is perfectly positioned to accumulate dust, dirt and a variety of other airborne particulates picked up throughout the house.

Sealed inside the air handler installed in the HVAC closet or up in the attic, the evaporator coil is not readily accessible to the average homeowner and its condition is rarely checked. When symptoms suggest dirty evaporator coils and an inspection by a professional confirms it, the cleaning process conducted by an HVAC technician is painstaking but thorough.

Typical Coil Cleaning Procedures

  1. Power to the A/C air handler is cut off at the thermostat or at the circuit breaker that controls the air handler.
  2. The coil access panel is usually secured by sheet metal screws and air-sealed at the seams by foil tape. After these are removed, the panel is lifted off to expose the evaporator coils. Most residential coils are in an A-frame configuration with a drip pan beneath the open angle of the coils to catch condensation. A drain line conveys condensate to a sewer connection or a drain point at the exterior of the house. 
  3. An HVAC technician has a number of cleaning methods at his disposal, depending on the condition of the coils.
  4. For light accumulations of common household dust on the outside coil surfaces, application of a commercially available coil spray cleaner may be sufficient to do the job. After the cleaner has been allowed to liquify and soak in, the air conditioner is started to form condensation on coil surfaces which flushes the coil clean. Removed dirt and cleaning solution drains away in the condensate drain. 
  5. Heavier accumulations of dirt, grime and chemical residue may be treated using a pump sprayer to inject cleaning solution deeper into coil passageways and reach inside coil surfaces. Care must be taken to control the pressure and application during the procedure to avoid bending the delicate coil fins. 
  6. In cases where inorganic matter is severely clogging the coils, a steam cleaner may also be utilized to dissolve dirt and grime. As with a pressure sprayer, care must be taken to limit the force of the steam and to ensure that the flow of steam is injected parallel to the coil fins to avoid bending. 
  7. Evaporator coils provide opportunities for hidden mold growth. Mold spores circulating continuously through the ductwork find a breeding ground in the wet passageways of the coil, as well as the condensate drain pan below. Mold growth that begins as a slick film on coil surfaces may grow to completely obstruct airflow through the coil. An evaporator contaminated with mold requires professional treatment with EPA-approved biocides to neutralize the mold in the coil, the drip pan and drain line.

After the Cleaning

Following the procedure to clean evaporator coils, the coil cover will be reinstalled and all seams sealed with metal foil tape. The A/C will be restarted and operated long enough to thoroughly flush the coil surfaces with condensation. The technician will also observe the condensate drain system to verify that condensation drains freely. 

Serving Chicagoland, Northwest Indiana and Southwest Michigan, Comfort24-7.com is your source for neighborhood heating and cooling experts. Contact us for more information about professional techniques to clean evaporator coils and restore performance and efficiency to your air conditioner this summer.

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