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 maintenace 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. 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 careful cleanup is important to protect indoor air quality.
Outdoor coils have no filters. Dirt collects in the coil depending on the quanity 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 loacted in a moist region with clean air, a coil may need cleaning just once a year.