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How Central Air Conditioning Systems Work

When it’s time to perform routine maintenance, or make simple troubleshooting, it’s helpful to understand how your central air conditioning system works.

Central air conditioning systems, are refrigerant-based systems cooling air in a single location, then blow the cooled air using a powerful fan and distributing it throughout the house using ducts. This system comes in two basic types: split-systems and packaged units.

There are eight main components in a Split-System Central Air Conditioning System, that play a pivotal role in cooling your home. A thermostat, condenser, compressor, fan, metering device, evaporator, blower and a filter.

The first step begins with setting your thermostat to the desired temperature. The thermostat triggers the condenser fan and compressor to turn on.

The compressor which is located in the outdoor unit, begins pumping a fluid called a ‘refrigerant’ throughout the system. The refrigerant is a fluid with low boiling point.
Refrigerant constantly changes from a vapor to a liquid in order to move heat from inside your home to the outdoors.

Refrigerant enters the compressor which is located outside of your home as a low-temperature, low-pressure vapor. After it’s compressed, it leaves as a high-temperature, high-pressure vapor. It then travels through the condenser coil, where the vapor condenses into a liquid and the heat it has collected indoors and after compression, is released outside.

The fan inside the outdoor unit helps with this process. The refrigerant leaves the condenser as a medium-temperature, high-pressure liquid. Then, flows to the metering device located on evaporator coil located in indoor unit.

In this case, a thermal expansion valve is used. A pin inside the valve adjusts the flow rate of refrigerant
depending on the temperature at the evaporator end, using a ‘sensing bulb’.

As refrigerant flows through the valve, its pressure drops significantly, releasing a low-temperature, low-pressure liquid/vapor mix. The lower pressure allows room temperature air to boil the refrigerant.

The chilled refrigerant then flows through the evaporator coil, inside the air handler and the blower begins circulating air throughout the house.

Room-temperature air is pulled in through the return duct and passes through the filter to remove particulates.
The heat from the air is absorbed into the refrigerant inside the evaporator coil, dispersing chilled air through the supply duct.

As the air passes over the coil, the refrigerant is boiled and evaporates back into vapor form again.

During this process, condensation forms on the outside of the coil and exits through a condensate drain line.

The refrigerant returns to the condenser to disperse the collected heat outdoors, and the cycle starts again. Your home is slowly cooled, and the thermostat shuts off the equipment once it senses the desired temperature.

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