Keeping the indoor coil of the air handler clean usually requires an air conditioning coil professional. This coil is usually buried inside the unit, behind the filter or an access panel. The coil is very delicate, and needs to be cleaned with the proper amount of air pressure and cleaning solution. Evaporator core cleaning, if done regularly from the time the coil is new and clean, can be done simply with a soft bristle brush, or low pressure forced air. Once the coil becomes more contaminated, a mild cleaning solution may need to be applied; this solution is left to sit for five minutes, then rinsed away.