The best way is to spray them out with your water hose making sure the water is pushed all the way through the coil to the inside. Keep spraying water through the coil until the water comes out clean on the other side. A coil cleaning solution can be purchased to be used for cleaning your condensing coils. Directions should be followed when using the cleaning solution. Not following cleaning solution directions can cause damage to your condensing coils.
Cleaning your coils should be done with a fair amount of pressure being sure not to bend coil fins over. Bending fins over will hurt the efficiency of your unit not allowing enough air to pass through the coil causing your system to run a high head pressure. A pressure washer shoud not be used to clean your condensing unit.