When an air conditioner fails to deliver the expected comfort level, many homeowners assume the internal coolness generator must have malfunctioned and immediately think they need an air conditioner repair.
That problem can be quickly ruled out because there isn’t any such component. Air conditioners are all about moving heat, not making coolness. The cool comfort you enjoy in your home provided by an air conditioner is merely a by-product of effective heat transfer. The functional difference between A/C evaporator and condenser coils is one of the principal forces that moves heat from here to there.
When Willis Carrier patented the first A/C in 1906, he called it an air conditioner, not an air cooler and for good reason. Carrier wasn’t primarily concerned with cooling the interior of the printing factory where he installed that first system. He mainly wanted to reduce indoor humidity to improve printing quality control. As it happened, his process that condensed humidity from the air also extracted heat energy, producing a cooler building as a side effect.
Today, as then, a mechanical process that effectively extracts indoor heat and moves it outdoors leaves behind cool comfort. The evaporator and condenser coils in an air conditioner are the system components that perform the heavy lifting of heat transfer, yet they function in exactly opposite ways.
A Quick Trip Around the Loop
The split system configuration of the central air conditioner installed in a typical residence incorporates a closed-loop refrigerant system. The lifeblood of the system is the refrigerant that continuously circulates between the A/C evaporator and condenser coils. Refrigerant is a chemical with very high heat-absorbing properties and the unique characteristic of changing state from a vapor to a liquid and back again under pressure.
The Evaporator Coil
Extracting indoor heat from the air and adding it to refrigerant is the function of the evaporator coil. Installed inside the indoor air handler, the evaporator is continuously exposed to the flow of warm air drawn by the system blower from individual rooms in the house through return ducts. Refrigerant circulating through copper tubes in the coil is a cold vapor around 40 degrees. In this state, the heat-absorbent properties of the refrigerant are maximized.
Heat energy from the warm house airflow transfers through the chilled copper coil tubing and is readily absorbed by the refrigerant flow. With its heat energy extracted by the coil, the cooled airflow is pushed by the blower into the supply ducts and dispersed throughout the house. At the same time heat is being extracted, the warm air contacting frigid evaporator coil surfaces triggers condensation, which lowers the humidity level in the airflow, “conditioning” the air just as Willis Carrier designed over a century ago.
After leaving the evaporator coil, refrigerant flows through an insulated conduit to the outdoor A/C component that’s usually directly behind the house. This cabinet contains both the compressor and the condenser coil. Refrigerant entering the compressor is pressurized, concentrating the molecules of heat energy and raising the temperature of the refrigerant vapor to over 100 degrees. This superheated state ensures efficient transfer of the heat energy into outdoor air, even when the outdoor temperature is high, such as on a hot summer day.
The Condenser Coil
The condenser coil is of similar design to the indoor evaporator coil. However, the difference between A/C evaporator and condenser coil is exactly reversed. While the evaporator coil picks up heat from indoor air, the condenser coil releases heat into outdoor air. The load of heat energy extracted from your home and compressed in hot refrigerant vapor is rapidly released when refrigerant circulates into the coil and condenses to liquid. As the refrigerant releases its heat load, a fan incorporated in the unit blows air through the condenser coil passages and heat is dispersed into outdoor air.
High-pressure liquid refrigerant leaving the condenser coil makes a u-turn and flows back to the evaporator coil. An expansion valve before the evaporator restricts the flow of refrigerant, forcing it through a narrow orifice and converting it back to a vaporized state, ready to absorb more heat energy from your home.
There’s no difference between A/C evaporator and condenser coils when it comes to the need to schedule an annual tune-up by a qualified HVAC contractor. It’s a critical part of maintaining your air conditioner to manufacturer’s specs for performance and efficiency. The individual maintenance requirements for each coil are affected by their differing functions as well as location.
Evaporator Coil Issues
Because the evaporator coil is continuously exposed to airflow circulated by the blower, it’s susceptible to buildup of dust or dirt. When airborne particles form a layer on coil surfaces, efficiency of the all-important heat transfer from the air to the refrigerant is diminished. This can result in poor cooling performance and higher operating costs as the system runs longer “on” cycles to meet thermostat settings.
Another factor specific to the evaporator coil is mold contamination. Dormant airborne mold spores are among the microscopic particulates circulating through the HVAC system airflow. Once these spores contact the surfaces of the coil that are wet from the condensation factor, the presence of moisture activates the dormant spores and active mold growth results. Like dirt and dust except more stubborn, mold growth on evaporator coil surfaces impacts proper heat transfer. Left to thrive, mold growth inside the coil air passages may eventually obstruct airflow entirely and cause the system to shut down.
Evaporator Coil Maintenance
In most systems, the evaporator coil is sealed within the air handler and may not be readily accessible to the average do-it-yourselfer. Annual maintenance by a qualified HVAC technician, however, includes coil inspection and cleaning to remove dust and dirt. If evidence of mold growth is noted, the technician will utilize EPA-approved biocides to disinfect the evaporator coil as well as the condensation drip pan under the coil.
Condenser Coil Issues
A major difference between A/C evaporator and condenser coils when it comes to maintenance is the fact that the condenser is located outdoors and exposed to the elements. Coil surfaces may accumulate windblown dust and dirt, as well as debris such as fallen leaves and grass clippings. On the other hand, because condenser coils don’t generate condensation moisture like the evaporator coil, mold is not usually an issue.
Condenser Coil Maintenance
Turning off the electrical power to the outdoor unit once a year and hosing down the coil with a garden hose is a good way to maintain condenser coil efficiency. In addition, the upper fan grille should be inspected for damage from fallen limb or other objects.
The outdoor condenser unit also requires open space on all sides to facilitate the free flow of air into the coil intake vents. Cut back any encroaching vegetation to create at least two feet of clearance around the unit.
Low refrigerant can affect performance of both the evaporator and condenser coils. When a new central A/C is installed, the indoor and outdoor units come pre-charged with refrigerant. In a competent professional air conditioner installation, technicians will measure the refrigerant level before installing and after the unit has been test-run. When this doesn’t happen and refrigerant is insufficient, the unit may chronically under-perform in terms of both energy efficiency and effective cooling. Ironically, low refrigerant levels may also cause evaporator coil surfaces to become excessively cold, freezing condensation and triggering a sequence of events that eventually culminates in coil icing which may shut down the system.
During annual maintenance by an HVAC technician, measuring the refrigerant level is also standard procedure. Air conditioners don’t use refrigerant the way an automobile may consume motor oil and require occasional topping up. If a low refrigerant level is detected, a leak is almost always the cause. Leak detection will focus on the evaporator coil, the condenser coil and connections in the refrigerant conduit.
To learn more about the difference between A/C evaporator and condenser coils and ensure that yours are in optimal condition, check out Griffith Energy Service’s regular A/C maintenance service.
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