Describe the problem:
Power unit down. Remove drain trap. Place custom cut "plug" panel on the bottom of filter tray, positioned to allow water to drain out the pan while blocking water from going down into duct. Using coil cleaner hose attachment, spray coil cleaner solution liberally into the fins/coils. Let sit for 5 minutes. Rinse thoroughly with water. Use plastic brush if necessary to loosen up debris. Repeat steps if not fully clean/shiny. Give final water rinse. Remove "plug" panel and power unit back on.