Arrived to do a maintenance on a York system vertical in closet. I cleaned and flushed the drain line with water and cleaner. I checked the electrical system. I changed the filter 16x20x1, owner had there own filter. I cleaned the condenser coils with water. I recommended the following to keep the system working like new: The surge protector is to keep from burning up the board on the condenser. If you get high power surges or lightning strikes in the area it may burn up the board. The start assist is to help start the condenser easier and last longer. The Uv light is to keep the biological growth out of the air handler and the air that you breath every day. The freeze protector is to keep from freezing up the coils in the air handler. If the blower fails or now air flow over the coils it will freeze the coils. The pan treatment is to keep the algae that builds up in the drain line out of the line and pan. The system is working great at this time. Thanks for using air no