Compressor/Condenser

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  The workhorse of a split central A/C system sits outside next to your house. Compressor/condenser sections come in many different shapes and sizes. Ailing units of any age can really make a racket, and older models are a bit noisier than newer ones, but you can hear all of them when they are working hard. The compressor is busy taking low-pressure refrigerant vapor returning from its cooling trip inside the house and pumping it at higher pressure toward the condenser. As the refrigerant condenses into liquid, it gives off the heat it collected inside, which is carried away from the condenser fins by a large cooling fan on top of the unit.
  
  

Refrigerant Lines

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  Refrigerant lines usually run side by side from the compressor/condenser unit through the wall of the house to the air handler/evaporator. Both lines should be insulated for protection from abrasion and to increase efficiency. The large line returns low-pressure refrigerant to the compressor while the smaller line carries high-pressure refrigerant on its way to the evaporator.
  
  

Air Handler/Evaporator

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  An air handler/evaporator is the section that actually cools your house. Some are located on top of or next to the furnace, while others are either partially or entirely in the attic. Inside the unit, finned evaporator coils sit within the flow of air created by a blower fan. As high-pressure liquid refrigerant enters the evaporator, a special valve creates a dramatic drop in pressure that returns the refrigerant to a vapor state. It is this change of state that creates the cooling effect, which is actually the refrigerant absorbing heat from the circulating air.
  
  

Ductwork

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  Air conditioning ducts run from the air handler to all the rooms of your house. Installers locate them wherever they can find space. Different parts of the ducting system can be found in your attic, walls, crawlspace or perhaps hiding in closets. There is at least one return duct as well to balance the air flow in the system. The return duct inlet is where you will find the system filter.
  
  

Controls

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  A simple central A/C system requires only a basic thermostat, although most modern units have at minimum a digital key pad and some degree of programmability. Units that combine heating and air conditioning with humidifiers/dehumidifiers and air purification systems need more complex computerized controls.