Condenser damaged dirt against fins. Since the evaporator condenses humidity from the air some moisture is present on the evaporator. This coupled with dirt and lint may cause the breeding of drain flies, mildew spores, etc. Often condenser radiators will be full of leaves or dirt, especially those sitting on the ground. To make the unit last longer and run more efficiently the radiator coils should be kept clean. Living in a dusty area, how often you change filters, and the location of the evaporator and/or condenser, will all dictate how often cleaning is required.