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Energy Saver: Air Conditioning
(continued ...) To summarize the refrigerant cycle, the compressor and expansion valve control the phase change of the refrigerant. The condenser and evaporator coils take advantage of the 'phase' of the refrigerant and 'moves' heat in the desired direction. See the article on Furnace, Boiler & Woodstove Combustion for an expanded discussion on phase change. Material phase change is a powerful tool used in many engineering processes.
Now, what can go wrong? The evaporator coil should have a filter in front of it such that the indoor airstream is filtered prior to entering the coil. Keep the evaporator coil clean and it is happy. See the article on Air Filters for a discussion on same. There is piping between the inside equipment and outside equipment that needs some discussion. The outside condenser coil needs yearly maintenance.
Let's start with that refrigerant piping. After the refrigerant leaves the condenser coil, it is as 'cold' as it can get in liquid form. The phase change process is where we are transferring the most energy. However, keep that refrigerant as cold as possible until it reaches the evaporator coil by insulating the pipe carrying it. It's possibly 100 F (38 C) outside and the pipe may be exposed to direct solar radiation. Once inside, you still want to keep it cold and now you also need to prevent condensation, which robs cooling energy from the pipe. Again, insulate it. After the refrigerant leaves the evaporator coil, the pipe may actually feel warm. While inside we don't want any of the heat re-released inside your house. Again, insulate it. After the return line is outside the refrigerant temperature maybe close to ambient but it could also be in the sun. I could go either way on this leg of pipe but likely I would recommend insulating it.