Unlike the common furnace, an air conditioner is a system of great complexity, something which is built on a number of mechanical conditions that must function in order for it to work correctly. Each mechanism is sized to meet a specific size in order to fit the “load” when the build commences. Both the amount of air flow across the internal coils and the amount of refrigerant are both huge factors in the system, and when either one of these fails to work properly, the whole system will begin to develop problems.
If, for a whole host of reason, the indoor heating in your home is at a high level due to the amount of people who occupy the space, the appliances that produce a lot of heat through the use of electricity or simply because of changes in the home, your air conditioning unit may start to falter as it struggles to keep up with the higher levels of demand from your home environment.
Given that the refrigerant charge of the system leaks, which it can, the capacity of the system could potentially begin to lower, depending on how much of this escapes in the process. Given this process happens, the cooling system will actually produce warmer air compared to the cold, so it won’t be able to keep up with the air when it gets hotter.
If the airflow amount across the outdoor coil is reduced, the ability to reject heat to the outdoor environment is reduced, again furthering the chance that the capacity of the system may be reduced, especially when the outdoor temperatures are high.
In dry climates, the same issues can occur when the indoor coil reduces as naturally, higher airflow will help the unit whilst lower airflow hurts the health of the air conditioning. In humid climates, the situation can become more complex as the hot air directly effects the performance of the unit. At higher airflows, there are less amounts of dehumidification, leading to high indoor humidities. If the airflow gets too low, however, the evaporator coil may freeze, which effectively breaks down the unit.