How Does An Air Conditioner Work?

With the temperatures nearing record heights this summer in Boston, air conditioning is on a lot of minds these days. I thought it would be valuable to take some time to explain how an air conditioner works. Knowing what your air conditioner is doing can help you take better care of it, and spot potential problems when they arise.

An air conditioner (whether it’s portable or stationary) has three major subsystems: the compressor, the condenser and the evaporator. All three systems need to be working well in order to provide cool relief from the summer heat. In addition to the major subsystems, an air conditioner has a refrigerant (also called a coolant) chemical that assists with the transfer of heat from the air inside your home to the air outside your home.

For the purpose of this blog, I’ll assume that we’re talking about a central air conditioner unit. Window units work in much the same way, except that window units have all of the subsystems in one package, so they must also handle the cool air distribution.
In a central air setup, the compressor and condenser usually remain outside the home, while the evaporator is located in or near the furnace, assuming that you have a gas/forced-air furnace. If you have a heat pump, your evaporator may be tied into or located near the air handler instead. In either case, the furnace or the air handler will perform the same function – distributing cooled air around the house.

The refrigerant flows around the air conditioning system and transfers heat to itself or to the outside air. Refrigerant is special because it can either be in gaseous form or liquid form, depending upon where it is in the cooling cycle.

The whole cooling process depends upon the unit’s ability to remove moisture from air. Hot air can carry a lot of moisture, but cool air can’t. If you remove the moisture from hot air, you get the side benefit of reducing the air’s temperature. Air conditioners (and refrigerators) remove moisture from the air by using a cold refrigerant to force the moisture in heated air to condense, and then evaporating the condensate.

At the beginning of the cycle, the refrigerant is gaseous. It is cool and under low pressure. The compressor compacts the gaseous molecules of the refrigerant together, placing them under higher pressure, which also raises the refrigerant’s temperature. The system then sends the refrigerant – which is now hot and under a lot of pressure – off to the condenser.

At this point, you have two things you don’t want: heat and gas. You really want the refrigerant to be cool and liquid. The condenser’s job is to get rid of the heat in the refrigerant while converting it to a liquid state. Because you’re working with twho things you don’t want, the condenser does it’s job outside!

The condenser is covered with many thin, metal fins, which help the heat dissipate from the refrigerant. A fan blows the heated air across the condenser coils. The fins increase the surface area of the condenser and give the heat more opportunity to get rid of heat. The refrigerant lets go of its heat and converts to a cool, high-pressure liquid. This cooled liquid refrigerant is sent to the evaporator through a very small-diameter hole, which helps it retain its liquid state.

The high-pressure liquid travels through the narrow channel to the evaporator. An expansion valve regulates the refrigerant’s trip to the evaporator. Once the refrigerant arrives, the pressure drops and it converts back to a gas. When a liquid converts to a gas, it absorbs heat. Some compounds are better at doing this than others, and refrigerants happen to be very good at absorbing heat while they convert back to their gaseous states. They also readily enter their gaseous states at relatively low temperatures.

As the hot air from the house hits the evaporator, the refrigerant inside begins to absorb heat and collect moisture out of the air. Like the condenser, the evaporator is also covered with thin metal fins, and uses a fan to help with the transfer of freshly cooled air from the system to the living space.

The refrigerant – once again in its gaseous, low-pressure state – is sent back to the compressor to start the process over again.

If you’re having trouble with your air conditioner, give us a call at Boston Standard Plumbing & Heating at (617) 288-2911. We work with all major brands of central air conditioners and can help you keep your system operating efficiently!
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