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How Your Air Conditioner Works

Air conditioning is the conditioning of air within a defined space. Conditioning usually involves heating or cooling, humidifying or dehumidifying, and filtering air. Central air conditioners cool and dehumidify a defined space. Heating is accomplished by an add-on to the system (such as an electric heat strip) or by a seperate unit (such as a furnace).


How Your Air Conditioner Cools the Air

Central air conditioners are split systems: an outdoor unit (the condensing unit) and an indoor unit (air handler). The function of an air conditioner is to transport heat from one station to another. The vehicle your system uses to carry the heat is called a refrigerant.

The compressor in your outdoor unit converts the refrigerant into a high temperature, high pressure gas. As that gas flows through the outdoor coil, it loses heat and condenses into a high temperature, high pressure liquid. This liquid refrigerant travels through copper tubing into the evaporator coil. There the refrigerant expands. Its sudden expansion turns the refrigerant into a low temperature, low pressure gas. This gas then absorbs heat from the air circulating in the duct work. The cooled air is then distributed back through your house or place of business. Meanwhile, the heat absorbed by the refrigerant is carried back outside through copper tubing and released into the outside air.

Dirty coils and improper refrigerant levels can cause your system to cool less efficiently than it should. An inefficient system means higher energy bills. It also forces your compressor to work harder than is necessary and can actually shorten the life span of your unit. An annual air conditioning inspection by an experienced technician includes an inspection of the coils and the checking of your refrigerant charge, to insure that your system is running efficiently.

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How Your Air Conditioner Dehumidifies the Air

As the warm air circulating through your ducts passes over the evaporator coil, it is quickly cooled and can no longer hold as much moisture as it did at a higher temperature. The excess moisture condenses on the outside of the coils and is carried away through a drain. The process is similar to what happens when moisture condenses on the outside of a glass of ice water on a hot, humid day.

Occassionally, the drain lines may become clogged and your system will not drain properly. This can result in a drain pan overflow, leading to water leaks in your ceiling or walls. An annual air conditioning inspection by an experienced technician should include an inspection of your drain lines and an algaecide treatment to retard the growth of algae. Consider having a float switch installed in your unit's drain pan. This switch will help to prevent water damage by shutting off your air conditioner should water back up in the pan.

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Heat Pumps

A heat pump cools your home or place of business by extracting heat from indoor air and forcing (pumping) the heat outdoors. For diagrams and a more detailed description on how heat pumps work, visit our Heat Pumps web page.

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The Importance of an Annual Cooling Inspection

Would you drive a car year after year without ever changing the oil or taking it to a mechanic for a tune-up? Probably not. Like your car, your cooling and heating systems must be maintained in order to run efficiently and dependably. An annual cooling check-up allows a technician to identify minor problems before they become major ones. The temperature outside should be in the upper sixties or higher to get an accurate refrigerant pressure reading. Also, the outside condenser unit cannot be opened and inspected when it is raining.

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Annual Fuel Utilization Efficiency. A measure of a furnace's heating efficiency. The higher the AFUE percentage, the more efficient the product.
Air Handler
Also known as the "indoor unit", the air handler is the evaporator section of your air conditioning system. It circulates and delivers the cooled air. The indoor unit contains the evaporator coil, an indoor fan motor and, sometimes, a heat strip (for supplemental heating).
Automatic Setback Thermostat
An automatic setback thermostat, more commonly known as a programmable thermostat, allows you to store six or more separate temperature settings for different times of the day. You can set the thermostat with a daily or weekly program. And you can override the settings at any time without affecting the daily or weekly program.
BTU stands for British Thermal Unit: the amount of heat required to raise the temperature of one pound of water one degree fahrenheit.
The compressor is the "engine" which drives the condensing unit. The condensing unit serves as a pump which compresses the gas in the high pressure (condensing) side of the cooling cycle and causes the refrigerant to circulate.
Condensing Unit
Commonly referred to as the condenser, the condensing unit pumps vaporized refrigerant from the air handler (indoor unit), compresses it, liquefies it, and returns it. It contains the compressor coil, an outdoor fan motor, refrigerant control valves, and other necessary controls.
EER Rating
The EER Rating (Energy Efficiency Ratio) is the ratio of BTU's to the amount of electrial power required to cool a home down to eighty degrees when the outdoor temperature is ninety-five degrees. Ask an AC technician for the EER rating on a new air conditioning unit and you may not get a straight answer. This is because the EER rating of a cooling system varies depending on the specifications of the various pieces of equipments (see Split Systems below), the grade of plenum used, and other factors. There is no simple formula for calculating the EER rating, but the technician must refer to charts furnished by the manufacturer and apply his knowledge of heatloads and the characteristics of your living spacing (ceiling heights, insulation, size and location of windows, etc...) to estimate the EER rating you will achieve with the new equipment.
Evaporator Coil
Found inside the air handler (indoor unit), the evaporator is where refrigerant vaporizes and absorbs heat.
Freon is the brand name of DuPont's R22 refrigerant. Over time the general public has come to use the word Freon for all R22 refrigerants, just as people commonly use the word Kleenex to refer to tissues or Xerox to refer to copies. Because R22 damages the ozone, the United States government is phasing out the use of all R22 equipment in homes and businesses. For more information on R22 and the restrictions being imposed on it, read Playing the Numbers - R22 vs. R410A.
Just as Freon is actually a brand of R22, Puron is Carrier's brand name for the refrigerant R410A. Air conditioners which run on R410A are generally more energy efficient and are more environmentally friendly than those which run on R22. Because R410A operates under much higher pressure than R22, it is important that the technician who installs or services R410A equipment in your home be well trained in this refrigerant. For more information on why the United States government is phasing out all R22 equipment and is imposing R410A equipment on American consumers, read Playing the Numbers - R22 vs. R410A.
Refrigerant is a substance which absorbs heat by changing states (evaporating) from liquid to gas. To legally buy and use air conditioning technician must own a recovery unit and must be EPA certified. Removing refrigerant without a recovery unit destroys ozone and is a violation of federal law.
Seasonal Energy Efficiency Ratio is the ratio of BTU's to the amount of electrial power required to cool a home down to eighty degrees when the outdoor temperature is eighty-two degrees.
Split System
The vast majority of central air conditioning systems presently used in southeast Texas are so-called split systems. These systems depend on two or three pieces of equipment to cool your home. The first is the condenser unit (or, in some cases, the heat pump) located outside your home. If your home is all electric, the second piece of equipment is your air handler, normally located in your attic (but sometimes found in an indoor closet or, in the case of mobile homes, beneath the home). The air handler contains an evaporator coil which works in tangent with the condenser to chill the air. The air handler also contains the blower motor which forces the cooled air through the supply air ducts. In the winter, a heat strip installed with the air handler heats the air which the blower motor forces through the ducts. If you have a gas furnace, your evaporator coil will be a completely separate unit. In these cooling and heating systems, the blower motor is located inside the furnace. While split systems are generally more expensive to install than package units, they are a lot quieter and they save the money in the long run because they are more energy efficient.
A temperature-sensitive switch that controls your heating and cooling systems. When the indoor temperature drops below or rises above the selected temperature setting, the switch moves to the "on" position, and your heater or air conditioner runs to warm or cool.

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