An experienced air conditioning technician looks for causes of evaporator coil leaks when tests reveal insufficient refrigerant in the system. Low refrigerant can be the root cause behind a number of A/C malfunctions from the subtle to the acute. These range from simply poor cooling performance to high operating costs to major component breakdowns like a compressor failure. While there might be any number of other explanations for these problems, low refrigerant is high on the list, particularly with older air conditioners.
The evaporator coil located inside the indoor air handler is a vital component in the air conditioning system. The coil circulates refrigerant vapor at a temperature of about 40 degrees. The refrigerant extracts heat energy from indoor air, which is drawn over the coil surfaces by the force of the blower fan. The warmed refrigerant then flows outdoors to the compressor/condenser component. Heat energy concentrated by the compressor cycle is dispersed into the outdoor air as the refrigerant circulates through the condenser coil, condensing into a liquid state. The flow of refrigerant then circles back to the evaporator coil, converting again to a frigid vapor to extract still more heat and keep the house comfortably cool.

Don’t Top It Up
A low refrigerant reading is usually indicative of a leak somewhere. While the leak may be small or large, “topping up” with extra refrigerant is nothing more than a temporary fix that won’t even get you through the next cooling season. A properly sealed and well-maintained A/C system will typically not require any extra refrigerant even after more than a decade of hot summers on the job. Identifying potential causes of evaporator coil leaks is usually a straightforward procedure, once a visual inspection and utilization of leak detection technology have evaluated all possibilities.
The Usual Suspects
Indoor and outdoor coils, as well as the conduits that convey pressurized refrigerant back and forth between them, are composed mostly of copper tubing with brazed joints and screw-type connections. As such, defective welds or loose connections are often suspected in cases of low refrigerant. However, leaks from defective welds or loose joints normally manifest very soon after a new air conditioner is installed and typically account for less than 5 percent of the cases of low refrigerant. Causes of evaporator coil leaks that occur in the four- to seven-year time frame of an air conditioner’s service life – a much more common occurrence – most often are due to degradation of the copper tubing inside the coil.

The More Likely Culprit
In a typical home, the evaporator coil is exposed to airflow rates of around 1,400 cubic feet per minute. The composition of the indoor air necessarily affects the condition of the coil. Building materials, furniture and common cleaning solutions slowly emit fumes called volatile organic compounds (VOCs), particularly formaldehyde, into indoor air. In a tightly sealed, energy-efficient house, formaldehyde fumes may accumulate to significant levels. In addition to the negative impact on healthy indoor air quality, concentrated formaldehyde reacts with condensation on the copper evaporator coil tubing to create formic acid – actually, the same substance that gives fire ants their notorious sting. Formicary corrosion of the copper results, slowly eating microscopic pinholes in the tubing and leaking refrigerant.
Here are some suggestions to eliminate formicary corrosion as one of the causes of evaporator coil leaks and low refrigerant in your air conditioning system:
Increase household ventilation with fresh outdoor air to dilute concentration of VOCs inside the house.
Install a whole-house air purifier inside the HVAC ductwork to treat the entire volume of air in the home as it circulates through the ducts multiple times per day. Many models incorporate an ultraviolet light array that degrades VOCs and eliminates the formation of formic acid.
Schedule regular A/C maintenance with your HVAC contractor. A qualified technician can inspect and clean the sealed evaporator coil with solutions formulated to neutralize formic acid, as well as remove the accumulation of dust and dirt that traps moisture on coil surfaces, another vital ingredient in formicary coil corrosion. Because a clean coil also transfers heat more efficiently, the system compressor runs shorter “On” cycles, reducing stresses on coil tubing from repeated pressurization and making leakage less likely.
For more information on tracking down the causes of evaporator coil leaks and taking positive steps to eliminate them, please contact the professionals at Superior HVAC . We proudly serve Houston and the surrounding communities.