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Central A.C. Explained with Words We All Understand

Have you ever stopped and pondered all the conveniences we utilize every day, seemingly with the touch of a button? You turn on the faucet and instantly water appears. You tap a few keys on your laptop and suddenly your video conferencing with someone on the other side of the globe. With a turn of the ignition, a car can transport you distances in one day that 200 years ago might’ve taken weeks. And then there’s air conditioning; without it, places like Las Vegas or Phoenix might still be tiny, out-of-the-way hamlets, and bingeing on the latest Netflix series during the hazy days of summer would be a sweaty enterprise. So how does this world-changing technology function? How does the so-called magic of air conditioning really work? Here is a nuts-and-bolts primer explaining how A.C. beats the heat.

Air conditioners operate by forcing refrigerants to evaporate and condense continually in a complex of coils and, thus, cool things down. These refrigerants absorb heat from your home in much the same way as water in a tea kettle absorbs the heat from your stove, and the heat is then expelled from a given area.

The standard setup of residential central air conditioning is the typical two-part, “split system,” which is comprised of a separate indoor and outdoor unit. The indoor unit is usually located in a basement, attic or closet, connected to a host of ducts that receive or discharge hot or cold air. The outdoor unit is often placed in the back or side yard. Inside each of these units is where the magic of home cooling takes place.

Refrigerant is the lifeblood of the cooling process, in that it circulates throughout the system continually, interacting with various hardware components to absorb and expel heat. In a sense, it’s a changing-state liquid/gas conveyor belt that collects heat from the inside to be delivered down the line and dispersed outside. But refrigerant needs assistance from other mechanisms to operate efficiently.

The furnace, or air-handler, uses a fan to draw in air throughout the home via return-air ducts which transport it through a filter in the furnace where dust and other airborne particles are quarantined. Here the low-pressure, cold refrigerant enters the evaporator coil which simultaneously: A) cools off the hot air and returns it back inside the home, and (B) heats and boils the cold liquid into a warm gas vapor.

From here the vapor makes its way to the outdoor section of the A.C. system, or “hot side,” where it intersects with the compressor. The compressor’s primary function is to keep the refrigerant moving throughout the whole process. If the refrigerant is the lifeblood of central air, then the compressor is the heart, pumping it to the unit’s vital organs, i.e. hardware. The coolant enters this area as a low-pressure vapor but leaves as a compressed, hot and high-pressure vapor.

Currently hot and at a high-pressure, the vapor embarks for the condenser where it is cooled by the condenser fan as it runs through finned coils that contour the outside unit. During this trek through the coils, heat is released into the open and blown away by a fan housed atop the unit. Now the refrigerant has once again morphed, from a hot vapor to a hot liquid, but still at a high-pressure where it encounters the expansion valve.

The expansion valve is established to decrease pressure from the refrigerant. The byproduct of this pressure reduction is heat loss and the cooled gas is now at its coldest point in the air conditioning cycle. Once again the refrigerant continues on its cyclical voyage, headed for the indoor evaporator coil to mix with the residual hot and humid air of the house and undergo the process again and again.

To most of us, the inner-workings of an air conditioner isn’t very glamorous but try to envision life without A.C. during the sweltering summer months.

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