How Air Conditioners Work

The majority of home and smaller commercial air conditioning systems circulate a compressed gas refrigerant in a closed “split” system to cool and condition inside air. The refrigerant has to be re-cooled and condensed, and outside air is the medium most often used to accomplish this. The term “split” simply means that components are divided into inside and outside portions as opposed to being located together in a “package” unit. The refrigerants, widely recognized by the trademark “Freon” (which is a registered trademark of the DuPont company for refrigerants), helps cool and dehumidify the inside air. In a “forced air” system, an internal blower circulates the conditioned air through ducts to the rooms where the cooler air is needed. The air ducts generally run either below the ceiling and inside the rooms (conditioned air) or in the attic (unconditioned air). An outside fan pulls air across the external parts of the system to cool and condense the refrigerant.

The major parts and functions in a split air conditioning system

Compressor – outdoors: The electric pump, or heart of the system, that circulates the refrigerant in a closed loop between the condenser and evaporator coils. Compressors come in more than one variety. According to Consumer Reports™ “A reciprocating compressor is more trouble-prone than a scroll-type one, they say. While pricier, scroll-type compressors do tend to be higher in efficiency and quieter than reciprocating compressors. Most manufacturers offer both types of compressor. ”

Condenser coil – outdoors: A network of tubes filled with refrigerant that remove heat from the heated gas refrigerant and convert the refrigerant into a liquid form again. The excess heat escapes into the outside air.

Condenser fan –outdoors- Pulls air through the condenser coil for heat dispersal.

Evaporator coil – indoors: A network of tubes filled with refrigerant that remove heat and moisture from the air as the refrigerant evaporates into a gas again.

Air handling unit – indoors- the blower and related portion of the central air conditioning system that moves air through the air ducts.

Air filters – Indoors: Air filter elements trap dust, pollen, and other airborne particles as air moves through the air conditioning system. Air filters contribute to both reliable air conditioner operation and health, so we dedicated a page to them.

Drainage system and pan- During the normal condensation process, an air conditioner produces a significant amount of water as a by-product. In a central A/C system, there is a primary system of pipes, often made of PVC, that carry this condensate water to the outside of the building. This piping needs periodic flushing to prevent it from getting stopped up with the algae and similar growth. At a minimum, this maintenance should be done by your service company during your annual system tune-up. Your inside A/C system should have an emergency drain pan in case the primary drain lines stop up. This pan usually comes equipped with an automatic cut-off switch that turns your air conditioning system off when then pan fills up with water. Otherwise, water will run out of the pan onto you ceiling or whatever is located below it. The need to flush the drain lines is a prime example of how a little preventive maintenance can prevent a major repair.

Air conditioning with a heat pump, often shortened to “heat pump” is a combination central air conditioning and heating system. In one mode, it functions as an air conditioner. In the reverse mode, it becomes a heater. Due to their unique design and special considerations, we have given heat pumps their own page on this website.

A brief history of air conditioning in the U.S.A. The first use of mechanical air conditioning (as we know it) began in 1902 in a New York print shop. Willis H. Carrier developed that system. Although he was not the first inventor to attempt to control indoor temperature and humidity with machinery, the safety improvements with refrigerants and success of Mr. Carrier’s system played a large part in the launch the modern air conditioning industry. A 1906 patent application by Stuart Cramer, a textile engineer, recorded the term “air conditioning” in a patent application for a humidifying device. Although it was first placed in a large residence in 1914, for the first twenty years or so, air conditioning was used mainly to control humidity and temperature to benefit industrial processes, not for human comfort. Carrier used air conditioners to enhance human comfort commercially in a department store and theaters in 1924. After gaining wider acceptance for the equipment in theaters and restaurants, in 1928 he developed the first air conditioner for private home use. That residential system went by the name “Weathermaker”.

The depression of the 1930s followed by the Second World War slowed the spread of air conditioning in homes. After the war ended, consumer demand picked up along with the baby boom. In 1952, housing developments began promoting the benefits of “central air conditioning”. Today, in all except the most temperate summer areas of the U.S., air conditioning is a standard feature in homes and businesses. Today’s air conditioning systems are more efficient and cost more upfront. Today’s central air conditioning systems are much more efficient than their predecessors. The industry uses a rating called SEER for central systems, which is an acronym for Seasonal Energy Efficiency Ratio. Essentially, a higher SEER rating means the air conditioner uses energy more efficiently. When other factors such as thermostat settings are kept equal, a higher SEER results in lower monthly utility bills for the owner or occupant. A central air conditioning unit rated at 16 SEER uses almost a third less electricity than a 13 SEER system. Some outside A/C units are rated at a range, such as 18/19 SEER, depending on what type of indoor equipment they are paired with. For example, if paired with a manufacturer recommended evaporator coil and a variable speed furnace or variable speed air handler, an outside unit could be rated as a 15 SEER system. Otherwise, the rating would be 14 SEER. As of January 2006, U.S. government regulations require all air conditioning manufacturers to produce residential central air conditioners with 13 SEER or higher. Between 1992 and January 2006, the minimum SEER rating was 10.As you might imagine, higher efficiency A/C equipment costs more to build. Why? For one reason, more efficient condensers and evaporators contain more metal in their extra coils. Additionally, to gain higher efficiency, the systems may have more complex technology such as motor speeds and electronics. If you are buying a new air conditioner, make sure you clearly understand the relationship between higher upfront costs and lower monthly utility bills of the more efficient equipment. The Energy Guide label clearly displays the SEER rating of all new A/C equipment.