A/C Made EZ

You crank up your AC on those hot New England days, but do you really know where that refreshing cool air comes from? Let’s take a look…


The key components of an air conditioner (and your refrigerator, by the way) are as follows: 1) the evaporator, 2) the compressor; 3) the condenser; and 4) the thermal expansion valve (or TX Valve). An air conditioner also has refrigerant that flows in a closed loop through the unit. A/C’s manufactured before 2010 use a refrigerant called R-22 (or Freon), while those made after 2010 use a modern refrigerant called R-410A, which is more efficient and environmentally friendly than R-22 (see our blog “Here’s Why You Should Recharge Your A/C Unit NOW” for more information). Just as fluids like water and propane can be in a gas or liquid state, so too can refrigerant. Refrigerant fluids change from liquid to gas at temperatures and pressures suited to cooling. So in an air conditioning system, the refrigerant might be slightly above 32°F (the refrigerant your freezer requires would be much colder).


The EVAPORATOR — Evaporators come in various forms, but a typical type consists of a “back-and-forth” length of copper tubing with metal fins attached. As the cold liquid refrigerant enters the evaporator it cools the tubing and the fins. A fan blows air across the cold fins, which remove heat from the air, thereby lowering the temperature of the air that gets emitted into the room. The removed heat is conducted through the metal to the refrigerant, where it is absorbed. As this happens, the refrigerant gradually changes from liquid to gas.


The COMPRESSOR — The refrigerant gas coming out of the evaporator is filled with the heat absorbed as it changed from liquid to gas. To make the refrigerant ready for more cooling, the A/C must get rid of that heat and convert the refrigerant back to a cold liquid again. To do that, the low-pressure gas coming out of the evaporator is sent to the compressor (which also serves as a pump that keeps the refrigerant circulating around the closed loop). As the gas is compressed its temperature goes up, and at the compressor output there is very hot high-pressure gas.


The CONDENSER — To this point your AC has not gotten rid of the heat picked up in the evaporator. The condenser enables the system to dump that excess heat into the atmosphere. Typical condensers are similar to evaporators, and have fans that blow air across their fins. Except in the condenser, the passing air picks up heat from the refrigerant — the opposite of what happens at the evaporator. In this process, the temperature of the high-pressure refrigerant drops to a point where it condenses back into a liquid. So the refrigerant enters the condenser as a high-pressure, high-temperature gas, and leaves in a much cooler liquid form.


The TX VALVE — The system is ready to create the cold liquid needed for the cooling process to continue. Reducing the pressure of a liquid refrigerant will cause its temperature to drop sharply. This is done by passing the liquid through the TX valve. As the refrigerant passes from the high-pressure zone to the low-pressure zone through the valve, its temperature falls to the level needed for cooling.


At this point the cycle is complete, with cold liquid refrigerant ready to enter the evaporator. The process is a continuous one, and at each point in the system there is always refrigerant “passing through” in the state described, working to keep your family cool on even the hottest summer days!