Finding a Refrigerant Leak: What Actually Works
Refrigerant is not consumed, so a low system has a leak. Here is how leaks are actually found and why "topping it off" is not a repair.
Refrigerant is not consumed in normal operation, so a system low on charge has a leak. Leaks are located using electronic detectors, UV dye, bubble solution, and nitrogen pressure testing. Adding refrigerant without finding the leak is a temporary measure that costs the same money again the following season.
The fundamental point
A refrigeration circuit is a sealed loop. The refrigerant inside it changes state continuously — liquid to vapor and back — but it is never used up, never burned, and never consumed.
So a system that is low on refrigerant is leaking. There is no other explanation. Any company that adds refrigerant annually without locating a leak is selling you a subscription to the same problem.
There is also an environmental and legal dimension. Knowingly leaving a significant leak while repeatedly recharging is not consistent with refrigerant handling regulations, quite apart from being poor practice.
How leaks are found
| Method | How it works | Best for |
|---|---|---|
| Electronic detector | Sensor responds to refrigerant vapor | General searching; sensitive but can false-positive |
| Bubble solution | Soap applied to joints reveals escaping gas | Accessible fittings and braze joints |
| UV dye | Dye circulates and glows under UV at the leak point | Slow leaks; requires time and a return visit |
| Nitrogen pressure test | System pressurized with nitrogen and monitored | Confirming whether a leak exists at all |
| Ultrasonic detector | Listens for the sound of escaping gas | Noisy environments where electronic detection struggles |
Where leaks usually are
- Evaporator coil. Formicary corrosion produces microscopic pinholes over years. The most common significant leak location.
- Braze joints. Especially on a system where connections were made without nitrogen flowing, which causes internal oxidation.
- Schrader valve cores. Small, cheap, and a frequent slow-leak source. Always worth checking first.
- Line set. Particularly where copper passes through a wall or contacts something that has abraded it over years.
- Condenser coil. Physical damage, corrosion, or vibration fatigue.
- Service valves and fittings. Loose or degraded seals.
The Schrader core point is worth remembering. It is the same kind of valve as a tire valve, it costs almost nothing, and a slowly leaking core can drain a system over a season while everyone looks for something more dramatic.
Why nitrogen testing matters
A nitrogen pressure test involves recovering the remaining refrigerant, pressurizing the system with dry nitrogen to a test pressure, and watching whether pressure holds over time.
It answers a question that is otherwise hard to settle: is there actually a leak, and is it significant? A system that holds nitrogen pressure for hours does not have a meaningful leak. One that loses pressure does, and the rate tells you roughly how large.
Nitrogen is also inert and inexpensive, so pressurizing with it is safe and does not release refrigerant.
On leak sealants
Sealant products injected into the refrigerant circuit are marketed directly to homeowners and sometimes used by contractors. We do not use them, and most reputable shops will not.
They circulate through the entire system and can clog metering devices, filter driers, and in bad cases reach the compressor. They also contaminate recovery equipment, which is why many companies will refuse to service a system that has had sealant added.
That last consequence matters most. A product intended as a quick fix can make you significantly harder to help later.
The repair decision
Once a leak is located, the decision depends on where it is and how old the system is.
An accessible braze joint, a Schrader core, or a service valve is a straightforward repair on a system of any age.
An evaporator coil leak on a system under eight years old is usually worth repairing, and the coil may be under parts warranty. On a system past twelve years it usually points toward replacement, because coil replacement is labor-intensive and you are investing significantly in aging equipment.
On an R-22 system, almost any significant leak repair argues for replacement. Production ended in 2020, remaining supply is expensive, and you are paying a great deal to refill a system that has already proven it leaks.
Frequently asked
Why does my A/C keep losing refrigerant?
Because it has a leak. Refrigerant is never consumed in normal operation — a sealed system that loses charge is leaking, and adding more without finding the leak means paying for the same problem again the following season.
How do technicians find refrigerant leaks?
Electronic detectors for general searching, soap solution on accessible joints, UV dye for slow leaks, and nitrogen pressure testing to confirm whether a leak exists and roughly how large it is. Difficult leaks sometimes require more than one method and a return visit.
Do A/C leak sealants work?
We do not use them and most reputable contractors will not. They can clog metering devices and filter driers and reach the compressor, and they contaminate recovery equipment — which means many companies will refuse to service a system that has had sealant added.