Clean the evaporator coil on an air conditioner using a stiff brush and gentle pressure to remove accumulations. Not all systems allow user access to the evaporator coil. On systems that allow access, clean the coil annually.
Before beginning any maintenance on an air conditioner, the circuit breaker should be in the off position. Access the evaporator coil by removing the foil-covered insulation from the front of the plenum. The plenum is the sheet metal box that connects the air handler to the duct system. Once the insulation is out of the way, an access panel is visible. Remove the screws that hold this panel in place to access the coils.
Clean the coils by brushing gently from underneath the unit. The evaporator unit should slide out, even if it connects using solid copper tubing; however, it is essential to avoid bending the pipes. Some units are too large to reach all the coils with the brush, but the user should remove as much dirt as possible.
Once the coils are clean, the owner should clean the drip tray. Diluted bleach water helps to kill any mold or bacteria growing in the tray. If the water is not draining, a stiff wire is useful for opening the drip tube.