If the coil is unclean, clean down with a hose pipeline on the coil only, but do not use a high-pressure hose or stress washing machine as this might create damages to the fins and the system. https://pipewiki.org/wiki/index.php/When_The_Scorching_Summer_Warm_Gets_Here_The_Last_Thing_You_Desire_Is_For_Your_Cooling_And_Heating_System_To_Damage_Down_On_You.