When an air conditioner stops cooling properly, many homeowners say the system is “low on refrigerant.” But in a sealed AC system, refrigerant does not get used up like gas in a car. If the refrigerant level is low, there is usually a leak somewhere in the system.
A refrigerant leak can happen for several reasons. Some are easy to understand, such as a loose connection or damaged copper line. Others are harder to see, such as tiny pinhole leaks inside the evaporator coil. One of the less familiar causes is called formicary corrosion, a type of copper coil corrosion that can quietly create very small leak paths over time.
The important point is simple: adding refrigerant without fixing the leak is not a real solution. The U.S. EPA also advises homeowners to ask technicians to locate and repair leaks instead of simply “topping off” the system, because repairing the leak helps the system run better while reducing refrigerant emissions and energy use.
What Is a Refrigerant Leak?
A refrigerant leak means that the cooling chemical inside the AC system is escaping from the sealed refrigerant circuit. This circuit normally includes the outdoor unit, indoor coil, refrigerant lines, valves, and connection points.
When refrigerant leaks out, the system may still run, but it cannot move heat as effectively. That can lead to weak cooling, longer run time, higher energy bills, frozen coils, compressor stress, and eventually system failure.
Common signs of a refrigerant leak include warm air from the vents, reduced cooling capacity, ice on the indoor coil or refrigerant line, hissing sounds near the system, oil stains around fittings, and repeated service calls to recharge refrigerant.
Common Causes of AC Refrigerant Leaks
1. Coil Corrosion
One of the most common hidden causes of refrigerant leaks is corrosion on the indoor evaporator coil or outdoor coil. The coil is exposed to moisture, airflow, household contaminants, and sometimes coastal or industrial air. Over time, certain environments can attack metal surfaces and create weak spots.
In copper coils, corrosion can sometimes lead to very small holes called pinhole leaks. These leaks may be difficult to see with the naked eye, but they can still allow refrigerant to escape slowly.
This is where formicary corrosion becomes important.
What Is Formicary Corrosion?
Formicary corrosion is a specific type of copper corrosion that can happen inside HVAC coils. It is sometimes called ant’s nest corrosion because, under magnification, the corrosion pattern looks like tiny tunnels inside the copper wall.
To a homeowner, the result is usually simple: the AC has a small refrigerant leak, often in the evaporator coil.
Technically, formicary corrosion is associated with tiny pinhole leaks on copper tubing. Industry research describes it as a corrosion pattern that creates microscopic tunnel networks through the copper wall, and the attacking agents are usually organic acids.
These organic acids may come from materials and products commonly found in homes, such as adhesives, cleaning products, paints, plywood, flooring materials, cabinetry, and other sources of indoor VOCs. Moisture and oxygen also play a role, which is why indoor air quality, ventilation, and the surrounding environment can affect coil life.
2. Poor Installation or Loose Connections
Not every refrigerant leak starts inside the coil. Many leaks happen at connection points, especially when the system is not installed correctly.
For mini split and split AC systems, flare connections, brazed joints, service valves, and refrigerant line connections must be installed carefully. If a connection is not tightened correctly, if the flare is damaged, or if the line set is not handled properly, refrigerant can slowly leak out after installation.
This is why proper installation matters as much as product quality. A well-designed system still needs correct pipe preparation, proper torque, clean connection work, pressure testing, vacuuming, and commissioning.
3. Vibration and Mechanical Stress
An AC system runs for many hours during hot weather. Over time, vibration from the compressor, fan motor, refrigerant movement, or poorly supported line sets can create stress on the tubing and joints.
If refrigerant lines are not properly supported, they may rub against sharp edges, walls, brackets, or other metal parts. Small vibration over a long period can eventually weaken the line or connection and cause a leak.
This type of leak is especially common when the installation area is tight, when the outdoor unit is not mounted firmly, or when line sets are bent too aggressively.
4. Physical Damage to Refrigerant Lines
Refrigerant lines can also be damaged during construction, renovation, landscaping, or service work. A nail, screw, lawn tool, or accidental impact can puncture or weaken the tubing.
Sometimes the damage is obvious. Other times, the line may only be slightly crushed or scratched, and the leak develops later.
For homes and light commercial buildings, this is why refrigerant lines should be routed, protected, and insulated properly, especially in exposed outdoor areas or busy mechanical spaces.
5. Aging Equipment and Long-Term Wear
As AC equipment gets older, seals, valves, coils, and tubing experience years of temperature changes, pressure changes, moisture, vibration, and environmental exposure. Even a system that was installed correctly can become more vulnerable over time.
Older systems may also use refrigerants that are more expensive or harder to service. When leaks become frequent, replacing the system may be more practical than repairing the same aging components again and again.
6. Harsh Outdoor or Indoor Environments
The surrounding environment can make a big difference. Coastal areas, high humidity, industrial zones, kitchens, laundry rooms, salons, workshops, and spaces with chemical cleaners or strong VOCs (Volatile organic compounds) can increase corrosion risk.
For outdoor units, salt air and moisture can attack fins, coils, cabinets, and fasteners. For indoor coils, household chemicals and VOCs can contribute to corrosion under certain conditions.
This does not mean every home will have a coil corrosion problem. The Copper Development Association notes that formicary corrosion is related mainly to certain chemical contaminants in the environment and is relatively rare compared with the total number of copper-tube heat exchangers in use.
But in the wrong environment, coil protection becomes much more important.
Why “Just Adding Refrigerant” Is Not Enough
A refrigerant leak should not be treated as a routine refill. If refrigerant is low, the leak needs to be found and repaired.
Adding refrigerant without repairing the leak can lead to the same problem again, and it may also increase operating cost and system stress. AHRI also advises equipment owners to ask technicians to repair leaks instead of topping off leaking equipment, because this helps protect performance and comfort.
For homeowners, the best question to ask is not only: How much refrigerant does my AC need?
The better question is: Where is the leak, and what caused it?
How Better AC Design Helps Reduce Leak Risk
A good AC system should be designed not only for cooling performance, but also for long-term reliability. That includes coil protection, stable refrigerant flow, strong connection design, quality manufacturing, and installer-friendly components.
For example, in environments where coil corrosion is a concern, enhanced coil protection can help reduce long-term exposure to moisture and corrosive elements. Anti-corrosion fin treatment, protective coatings, carefully selected heat exchanger materials, and improved manufacturing processes can all support better durability.
This is also where product selection matters.
How ZERO Helps Protect Against Refrigerant Leak Risks
ZERO mini split systems are designed to reduce leak risks from the material level. For selected indoor units, ZERO uses TU1 copper, a high-purity copper material engineered for better resistance against formicary corrosion, one of the hidden causes of pinhole refrigerant leaks in AC coils.
Compared with traditional TP2 copper, ZERO’s TU1 copper offers higher copper purity, improved corrosion resistance, and better heat transfer performance. According to ZERO lab testing under a 1000-hour formicary corrosion simulation, TU1 copper showed a much lower perforation ratio than standard TP2 copper, helping reduce the risk of coil-related refrigerant leaks.
This type of protection is especially valuable in hot, humid, coastal, or high-use environments where AC systems need to run for long hours.
ZERO also focuses on installation-friendly system design. Complete installation kits, matched components, clear product documentation, and reliable system construction help reduce problems related to poor connection work, line set mismatch, and unnecessary installation complexity.
For installers, this means a smoother installation process. For homeowners, it means better peace of mind.
A refrigerant leak can come from many sources: corrosion, loose fittings, vibration, physical damage, aging parts, or harsh environmental conditions. No product can remove every risk. But a better-designed system can help reduce the most common weak points from the start.
Final Takeaway
A refrigerant leak is not just a small service issue. It is a sign that something in the system needs attention.
Sometimes the cause is a visible damaged line. Sometimes it is a loose connection. Sometimes it is a hidden pinhole leak caused by copper coil corrosion, including formicary corrosion.
The best solution is to choose reliable equipment, install it correctly, maintain it regularly, and repair leaks instead of simply refilling refrigerant.
With corrosion-resistant coil protection, practical installation support, and system designs built for real-world conditions, ZERO helps homeowners and contractors reduce leak risks and keep comfort running longer.
Looking for a split AC system built for long-term reliability? ZERO split AC systems are designed with corrosion-resistant coil protection, installation-friendly components, and dependable performance to help reduce common leak risks and keep comfort running longer. Explore ZERO split AC solutions for your next project: zerohvacr.com
