Trouble shooting tips for frozen evaporator coil

Sep 14,2015

Frozen Evaporator Coils Causing Problems? Use These Trouble shooting Tips.

Frozen evaporator coils might sound like a good thing. After all,the evaporator coil is the component responsible for extracting heat fromindoor air, so the colder the better, right? Wrong. While an evaporator coilshould be frigid, it should never be freezing. Frozen evaporator coils coatedwith ice can cause an assortment of air conditioner & refrigeration problems ranging from annoyance to majorcomponent damage. And the fact that the coils are cold enough to produce ice isitself a symptom of dysfunction somewhere in the system.

How It Works?

Here’s the short versionof how an evaporator coil functions. Refrigerant vapor flowing through the coilat about 40 degrees has very high heat-absorbing properties. As the systemblower fan pulls warm indoor air through the coil, heat energy is extracted fromthe air and transferred into the refrigerant flow. At the same time, watervapor is continuously condensing out of the air and dripping down into thecondensate drain pan. The refrigerant flows to the condenser coil in theoutdoor half of the system, where the heat is released into outside air.Meanwhile, what’s left behind indoors is cooled air dispersed through the ductwork.

What Can Go Wrong?

Ice forms on anevaporator coil when the coil temperature drops below 32 degrees. This causescondensation removed from the air to freeze on the coil. As layers of ice buildup, airflow through the coil begins to be restricted. Eventually, a frozen coilwill severely obstruct system airflow. Irreversible damage to expensive componentslike the compressor or blower fan may occur as the strangled system runsnonstop without reaching the thermostat setting.

Unless the problem isnoted, a safety overload switch may shut the system down entirely or a majorcomponent may fail. Meanwhile, ice formation on the coil may grow to a sizethat causes water damage when it rapidly melts after the system shuts down.

Why Frozen Evaporator Coils Happen

Low airflow: If the air volumepassing through the coil is below system specifications, insufficient heatenergy is transferred into the refrigerant flow. This causes the refrigeranttemperature to plunge below freezing and triggers ice formation on the coil.The most common cause of insufficient system airflow is usually a very dirty orclogged air filter. Change thefilter and see if that resolves the icing problem.

Another cause of low airflow that you can check yourself areblocked air return vents in individual rooms. A failing blower motor may alsodecrease airflow below specs and cause frozen evaporator coils. A qualifiedHVAC technician can check the blower performance to isolate this problem.

Low refrigerant charge: When there’s not enoughrefrigerant circulating through the system, coil temperatures drop below 32degrees and ice forms. At proper refrigerant pressure, the temperature of therefrigerant stays around 40 degrees. However, when the level in the system islow and refrigerant pressure declines, the refrigerant temperature drops belowfreezing and condensation on coil surfaces turns to ice.

Air conditioners don’t use up refrigerant. If the refrigerant chargeis low, it’s nearly always the consequence of a leak somewhere in the system.Pinpointing and repairing the leak requires the expertise and special leakdetection equipment of a trained HVAC service tech.

Dirty coil: Dirt or dust accumulation on coil surfacesinterferes with proper heat transfer out of the air. Just as with low airflowissues, when insufficient heat transfers into the refrigerant, the temperatureof the refrigerant drops below freezing and ice formation results. Mostevaporator coils are sealed inside the air handler andaren’t easily accessible for DIY cleaning. However, evaporator coil inspectionand cleaning are part of an annual A/C tuneup servicefrom your local HVAC contractor. This keeps the coil clean and prevents frozenevaporator coils. Annual tuneups are also critical to sustain system energyefficiency, optimum performance and maximum service life.





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