Air Conditioning 101

Most residential air conditioning systems are electric compressor-cycle systems. This type system includes the basic window or through-the-wall unit, as well as central (whole house) air conditioning systems. Central air conditioning systems are typically either packaged units, which have all major components in one housing (similar to a room-style unit), or split systems, which have a portion of the system in a cabinet outdoors and a blower and other components in an indoor air handler cabinet or within the basic cabinet of a furnace.

Regardless of the style of the system, the basic components and method of operation are similar for all electric compression-cycle systems. The major elements are an evaporator coil, a condenser coil, fans to circulate air over both coils, tubing to carry a refrigerant between the two coils, a compressor to move the refrigerant through the system, and a metering device to regulate the rate of refrigerant flow.

Air conditioning systems use several basic principles of physics to remove heat from within a house: (1) a refrigerant absorbs heat when it changes from a liquid to a gas; (2) a refrigerant releases heat when it changes from a gas to a liquid; and (3) heat moves from a medium at a high temperature to a medium at a lower temperature.

As the liquid refrigerant passes through an expansion device into the evaporator it expands to a gas. At the same time, it absorbs heat from the household air, which is forced by the air handler fan through the evaporator coil. As this heat transfer takes place, the temperature of the household air becomes noticeably cooler and is forced through air ducts to the rooms of the house. The refrigerant, which vaporizes into a gas in the evaporator, is pulled through the tubing into the compressor where it is compressed to a high-temperature, high-pressure gas. This gaseous refrigerant then passes into the condenser coil where it gives up heat to the relatively cooler outdoor air, which is forced across the coil by second fan. In the process, the refrigerant condenses back to a liquid and is ready to begin another cycle.

One other issue to consider is that an air conditioning system not only removes heat from the air, but it also dehumidifies the air. For comfort cooling, a balance of temperature and humidity must be maintained. This means that the unit must be sized properly so that it runs long enough to dehumidify the air before the thermostat temperature settings are satisfied. An oversized system in a hot, humid climate will not maintain the proper comfort level, as the air will be cooled before a reasonable humidity level is attained.

Adequate airflow is important for the proper operation of an air conditioning system. Dirty filters and blocked or improperly positioned air inlets (returns) and outlets (supply registers) will result in imbalanced air distribution and uneven cooling. At least one return needs to be positioned near the ceiling.

Central air conditioning systems do not require a burdensome amount of maintenance, but some basic attention is required if the unit's maximum economic life span is to be achieved. The first major element that may require replacement is usually the compressor. Unfortunately, it is also the most expensive component of the system. Manufactures typically provide five-year warranties on the original compressor, but with system maintenance most compressors will last well beyond that period.

An annual check and servicing of all central air conditioning systems by a qualified HVAC service company is recommended. In addition, to help attain the maximum comfort and trouble-free service life for their system, homeowners are also advised to following these maintenance and operation guidelines:

• Reset dampers for air conditioning at the start of the cooling season. A damper adjustment is required only if there are separate ducts for the cool air and if the return has both a ceiling and floor register.
• Check to make sure all supply outlets and returns are free from obstructions and dust.
• Clean and/or replace air filters monthly (in season). Service the electronic air cleaner if you have one.
• Check to make sure the condensate drain extending from the evaporator area is draining freely. If there is an overflow pan under the unit, as is the case in many attic installations, be sure the pan is clean and the condensate drain open. If your unit has a condensate pump, keep it clean and working.
• Find a comfortable setting above 78 degrees F and don't change it. Consider installing a programmable or set-back thermostat.
• Make sure all ducts that pass through hot areas such as attics, garages and crawlspaces are insulated.
• Minimize heat gain and hot air infiltration by providing adequate attic insulation and weather-stripping at windows and doors.
• Make sure there is adequate attic ventilation.
• Never operate a house air conditioning system when the outside temperature is below 60 degrees F.

Remember, these tips are only general guidelines. Since each situation is different, contact a professional if you have questions about a specific issue. More home safety and maintenance information is available online at lightcap.housemaster.com.