Most air conditioning systems function using five primary components. Additional components, such as ducts, may be used to distribute the air throughout the home. Following is a closer look at the basic components of every AC unit, a few of the additional components that most units include, and a breakdown of the standard cooling cycle.
The five basic components of every AC unit are the condenser coil, the evaporator coil, the compressor, the fan, and the refrigerant. The standard AC divides these components into two categories. On one end is the “hot” side, which is located outside of the home. The “cool” side is located on the inside of the home.
The hot side of the AC unit contains the condenser coil, compressor, fan, and various electrical components. The cool side is primarily the evaporator coil, which is often installed above the furnace. If you have gas, then it will be installed near the standard gas furnace. If you have a purely electrical AC unit, then it will have its own independent electric furnace. Gas and electric AC units work the same way just with a different energy source.
The Role Of Refrigerant
The cooling cycle works thanks to the chemical properties of the air conditioning refrigerant used. There are two important physics concepts at work. First is the combined gas law. This law states that whenever gas is heated up it also increases the pressure. Likewise, whenever you increase the pressure of gas it also increases the heat.
You’ve probably encountered this law in action in other places as well. For example, when you spray an aerosol can the pressure inside decreases and causes the can to get colder. When you pump air into a tire it gradually heats up. The same thing is happening inside of an air conditioner as the refrigerant is pressurized or depressurized to control temperature.
The other physics law in play is the 2nd law of thermodynamics. This law simply states that will heat will naturally flow from hot areas to cold areas. Using the combined gas law and the 2nd law of thermodynamics together makes it possible to control the heat inside of a particular part of an AC unit and then transfer that heat to a colder area.
The refrigerant works together with the four other basic components mentioned earlier to do exactly this. A common misconception is that an AC is actually creating cold air. In reality, it is removing heat from the incoming air and then blowing that air into the home. The heat is then distributed outdoors thanks to the 2nd law of thermodynamics. Thus, the AC unit is constantly moving heat from the inside to the outside of your home.
The Role Of The Compressor
For the refrigerant to work it must constantly cycle through the AC unit components. It changes its state various times during this process. The compressor can be thought of as the heart of the unit. It is responsible for pumping the refrigerant through the different coils in the unit.
The compressor is also responsible for controlling the pressure in the unit and the flow rate of the refrigerant. The necessary flow rate and pressure will vary according to the size of the AC unit and the type of refrigerant being used.
Refrigerant enters the compressor in a vapor state. It enters on the low-pressure side, also known as the suction side. The compressor then pressurizes the vapor refrigerant. This increase in pressure also causes an increase in temperature because of the combined gas law mentioned previously. This is in addition to the heat that the refrigerant had already absorbed from your indoor air. Once the temperature of the refrigerant is significantly higher than the temperature outside it will begin to flow outdoors towards the next component: the condenser.
The Role Of The Condenser
An outdoor fan continually blows air over the condenser coils. The heat energy leaves the refrigerant and is transferred to that air, which makes it way over the coils and back outside. This is why if you were to put your hand over the fan on the outdoor unit of your AC you will feel very hot air blowing.
The sudden cooling of the refrigerant causes it to change states of matter. At a low enough temperature it will change from a vapor into a liquid; hence the name “condenser coils”. Most of the heat that leaves the refrigerant into the outdoor air is the heat that was absorbed from inside the home.
The next essential component is the evaporator coil, but in between the two is the metering device. The metering device is usually a thermostatic expansion valve and it represents a divide between the high pressure and low-pressure sides of the AC system. The purpose of this device is to decrease the pressure of the refrigerant very quickly to cause a severe drop in temperature. This is necessary because the refrigerant is not yet cold enough to absorb more heat from indoors.
The Role Of The Evaporator
The metering device lowers the refrigerant pressure until it is colder than the indoor air. It then immediately flows into the evaporator coils indoors. An indoor fan blows air from inside your home across the evaporator coil. Heat moves from that indoor air into the liquid refrigerant because of the difference in temperature. This causes the refrigerant to increase in temperature and return to a vaporized state.
The air that was blown across the evaporator coils decreases in temperature. That is the air that is blown through the ducts and that keeps the house nice and cool. As for the refrigerant, it is sucked back into the low-pressure side of the compressor where it can begin the cycle all over again.
There are several additional components in most AC units. These are primarily electrical components, such as computer controls or digital thermostats. There are also air filters used to keep particulate matter out of the air flow. Most homes use fans and ducts to deliver the cold air to different rooms in the home. Together, all of these components form the standard home AC system.