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Shut off the power to the air conditioner. Take the air conditioner out of the window (when applicable). Trim foliage so it isn't closer than 2 feet (0.6 meters) to the unit. Remove the cover from the air conditioner unit. Pull the cover and fan from the unit (when applicable).
Most outdoor air conditioning units have an appliance shut off box situated nearby. Open the door on the box and flip the switch or remove the fuse to cut power to the air conditioner. Window and wall units can usually just be unplugged.  If you have no shut off box, turn off the power at the circuit breaker in your house. Never attempt to work on an air conditioning unit without first disconnecting the power. Window units can usually be cleaned just like central air units, but the coils will be easier to access if you remove the unit from the window before you start working on it.  The layout of window units is different than indoor or outdoor central air units, but the functions and parts are effectively the same. Be sure to lay the air conditioner on a flat surface, preferably outdoors, for cleaning. As the seasons change and leaves fall from trees, they can collect on the air conditioning unit or even slip inside through the heat dissipation vents. Once you've trimmed the branches and bushes, be sure to clear the entire area around the unit.  Loose leaves and dirt surrounding your air conditioning unit can be blown through the vents, collecting around the coils and limiting how effective they can be. Cleaning the area of debris and foliage will also improve airflow into the air conditioning unit. Be sure to wear safety glasses and gloves when trimming trees and bushes. Depending on your air conditioner, you will need either an appropriately sized socket or a screwdriver to remove the bolts or screws securing the cover in place. Once you have them removed, pull the lid off of the air conditioning unit.  The user manual will tell you what size socket or screwdriver you need. Set the screws aside somewhere safe. Some air conditioning units will have a grill with a fan attached to it mounted on the top. Remove the screws and pull the grill out from the top of the open unit. The fan is usually attached, so be sure to support it as you remove the assembly to avoid letting it hang by its electrical connections. In air conditioners where the fan stays in place, avoid spraying it directly with water as you clean.