How an air conditioner works

The job of your home air conditioner is move heat from inside your home to the outside, thereby cooling you and your home. Air conditioners blow cool air into your home by pulling the heat out of that air. The air is cooled by blowing it over a set of cold pipes called an evaporator coil. This works just like the cooling that happens when water evaporates from your skin. The evaporator coil is filled with a special liquid called a refrigerant, which changes from a liquid to a gas as it absorbs heat from the air. The refrigerant is pumped outside the house to another coil where it gives up its heat and changes back into a liquid. This outside coil is called the condenser because the refrigerant is condensing from a gas back to a fluid just like moisture on a cold window. A pump, called a compressor, is used to move the refrigerant between the two coils and to change the pressure of the refrigerant so that all the refrigerant evaporates or condenses in the appropriate coils. The energy to do all of this is used by the motor that runs the compressor. The entire system will normally give about three times the cooling energy that the compressor uses. This odd fact happens because the changing of refrigerant from a liquid to a gas and back again lets the system move much more energy than the compressor uses.

What goes wrong

Unlike most furnaces, air conditioners are complex mechanical systems that depend on a wide variety of conditions to work correctly. They are sized to meet a certain “load” on the house. They are designed to have certain amount of refrigerant, known as the “charge”. They are designed to have a certain amount of airflow across the coils. When any of these things changes, the system will have problems.If you produce more heat indoors either from having more people or appliances or because of changes in the house, the air conditioning may not be able to keep up.

If the refrigerant charge on the system leaks out, it lowers the capacity of the system. You will simply get less cooling and system will not be able to keep up when the load gets high.

If airflow across the outdoor (condenser) coil is reduced, the ability to reject heat outdoors is reduced and the again the capacity of the system may go down, especially at higher outdoor temperatures.

What those filters do

Almost every air conditioning system has a filter upstream of the evaporator coil. This can be in the return grille or in special slots in the duct system and can be a fuzzy-looking or a folded paper filter. This filter removes particles from the air stream to both keep the air conditioning system clean and to remove particles from the air.As the filter does its job, it gets loaded with more and more particles. This actually has the effect of making it more efficient, but it also increases resistance and reducing airflow. When this happens, it is time to change the filter. How long it will take to happen depends on how dirty the air is and how big the filter is.

If you don’t change the filter, the air flow will go down, and the system will not perform well. Not only that, but if the filter is too dirty, it starts to become a source or air pollution itself.

If airflow across the outdoor (condenser) coil is reduced, the ability to reject heat outdoors is reduced and the again the capacity of the system may go down, especially at higher outdoor temperatures.

How to increase energy efficiency

Sealing leaky ducts may be the biggest single thing you can do to improve efficiency, but a lot of the issues mentioned about will help as well: replace dirty filters, keep the right charge and airflow, clean the coils.Another thing to do is to make sure the outdoor (condenser) unit is not so hidden from sight that its airflow is blocked or that leaves or other matter are not clogging it.

If airflow across the outdoor (condenser) coil is reduced, the ability to reject heat outdoors is reduced and the again the capacity of the system may go down, especially at higher outdoor temperatures.

It’s not the heat, it’s the humidity

Humidity control was the problem that originally spurred the need for air conditioning. Lack of humidity control in hot, humid climates, in particular, can lead to mold growth and other moisture-related problems. High indoor humidities can lead to health and comfort problems.

Modern air conditioners dehumidify as they cool; you can see that by the water that drains away, but this dehumidification is incidental to their main job of controlling temperature. They cannot independently control both temperature and humidity.