Dirt on air-conditioning coils is a serious maintenance problem in residential or commercial buildings. Dirty coils reduce airflow, decrease efficiency, reduce HVAC capacity, and are a major cause of compressor failure and sick building syndrome. For maintenance purposes we divide coils into two types: indoor coils and outdoor coils.
Indoor coils are located in the air handler and they have filters. Filtering is important because indoor coils are located in tight spaces within air handlers or ducts and so they are difficult and expensive to clean. Filters should be changed whenever they become dirty. Pressure gauges, filter indicator lights, and filter alarms alert maintenance staff in some facilities to ensure timely filter replacement. Indoor coils also have drain pans that require careful cleaning to prevent their accumulated debris from becoming airborne and polluting the building’s air. It requires care to contain the mess created by coil cleaning, but containment and careful cleanup is important to protect indoor air quality.
Outdoor coils have no filters. Dirt collects in the coil depending on the quantity of particulates in the outdoor air. If the coil is located in an industrial area or near a dirt road, it may need cleaning every two or three months. If located in a moist region with clean air, a coil may need cleaning just once a year.
Wet vacuuming while spraying with high-pressure cold water is probably the most effective and safe way to clean dirty coils. Coils collect dirt on the side where the air enters. High-pressure water pushes dirt out the same way it came in. This is a procedure best practiced by professionals, because the coil’s aluminum fins bend easily if the high-pressure water is sprayed at the wrong angle. Hot water and steam aren’t used to clean evaporator and condenser coils because they create excessively high pressure within the coil’s piping.
Surface dirt and debris can be removed from any coil using a stiff bristle brush or wire brush. HVAC technicians also use a variety of commercial cleaning agents to remove dirt from deeper in the coils. Biodegradable detergents are the safest coil cleaners and should be used whenever they can effectively loosen a coil’s embedded dirt. However, alkaline and acid cleaners are sometimes necessary. Acid cleaners work well to cut fine particulates like smoke that accumulate on outdoor coils. Alkaline cleaners are effective at cutting greasy dirt encountered on indoor coils. Grease comes from skin flakes and cooking. Using powerful cleaners requires experience and extreme caution, especially indoors where fumes could sicken the technician or building occupants.
Filter racks should completely fill the airway and be sealed at their edges to prevent dirty air from circumventing the filter.