Refrigeration-Leak Detection
All sealed systems leak. The leak could be 1 pound per second or as low as 1 ounce every 10 years. Every pressurized
system leaks because “flaws” exist at every joint fitting, seam, or weld. These flaws may be too small to detect with
even the best of leak detection equipment. But given time, vibration, temperature, and environmental stress, these
flaws become larger detectable leaks.
It is technically incorrect to state that a unit has no leaks. All equipment has leaks to some degree. A sealed system
which has operated for 20 years without ever needing a charge is called a “tight system.” The equipment still has
leaks, but not enough leakage to read on a gauge or affect cooling performance. No pressurized machine is perfect. A
leak is not some arbitrary reading on a meter. Gas escapes at different times and at different rates. In fact, some leaks
cannot be detected at the time of the leak test. Leaks may plug, and then reopen under peculiar conditions. A leak is a
physical path or hole, usually of irregular dimensions. The leak may be the tail end of a fracture, a speck of dirt on a
gasket, or a microgroove between fittings.
Leak-check methods
As service technicians face an increase of leaking systems, employing proper leak-detection methods is critical to A/C
and refrigeration service. Service technicians use at least one leak-detection method; however, equipment for six
methods may be on hand and used until a leak is found.
The six most common techniques include:
1. Visual checks
2. Soap-bubble test
3. Nitrogen pressurization hold test
4. Electronic leak test
5. Ultrasonic detection
6. UV-dye injection.
7. Vacuum pump
These techniques are not new, but because of the increasing occurrence and difficulty of finding leaks, all six
methods have a place and a time in the leak-detection process.
Visual checks
The adage, “look before you leap,” applies to the first leak-detection technique. The first inspection should investigate
unusual colored markings or dirt buildups around joints or on piping. Too many technicians disregard this potentially
quick diagnosis in favor of resorting to the industry’s higher technology leak-detection tools.
Soap-bubble test
Super soap solutions are still tried-and- true leak tests since refrigeration evolved in the early half of the 20th century.
Soap is fast, and it is very visual in that the exact leak point can be seen.
Nitrogen pressurization hold test
Recovering a system’s refrigerant and then pressurizing it with nitrogen at 150 psi is a good method of leak detection.
The holding process should be observed for at least 10 minutes. If the system loses any pressure over the course of 30
minutes or more, then it is a sure indication the system is leaking. Nitrogen pressure hold tests can also indicate a
small leak or if the system has a large or multiple leaks. A 10% or larger psi drop most likely indicates large or
multiple leaks. Some leaks are not detectable until the system operates, and so nitrogen has some
disadvantages. Never leave an unattended nitrogen tank pressurized on the regulator, which can leak and infiltrate
the system with too high a pressure.
Electronic leak test
While the system is nitrogen charged, a small 10% charge of refrigerant can be used so that electronic leak
instruments—such as infrared absorption, heated diode and corona discharge—will have refrigerant to detect. Many
service technicians incorrectly assume refrigerant is projected at a 90-degree angle from the piping run, thus, they hold
their sniffer at that angle. However, laboratory research leak-mapping reveals all leaks have a unique shape that causes
refrigeration projection in any possible direction. Therefore, electronic sniffer paths should be in a circular motion
along the pipe.
Ultrasonic detection
Sensing ultrasonic frequencies of exiting refrigerant can many times discover leaks beyond electronic detection
capabilities. A good tip is that ultrasonic test instruments are better at sensing nitrogen-filled systems vs. those with
the original refrigerant. Nitrogen has a lower specific volume, which allows it to leak at faster velocities and produce
high frequencies in the ultrasonic range. Another advantage of ultrasonic leak tests is they pinpoint the exact leak or
indicate multiple leaks in a given area.
UV-dye injection
When all else fails, UV-dye injection can help to pinpoint leaks. It leaks out of an exit point with the refrigerant and
leaves dye residue that can be detected easily with UV detection lights. The five previous methods all depend on
continuous leaking and are not helpful in intermittent leaking incidences. UV dyes can detect a continuous leak, but
can also find intermittent- leak-residue evidence that a service technician will be able to see days and even months
later. Independent laboratory data reveals that approximately 35% of refrigeration leaks have an intermittent
characteristic. Because POE oil absorbs water so easily, moisture-resistant UV dyes are critical. Dyes that are less
resistant to moisture can break down into ineffectiveness or clog filter-driers and cause uneven pressure differentials
that are higher upstream and lower downstream.
Vacuum pump
Vacuum is used to evacuate e the refrigerant from any system, leak can be detected after completing the evacuation
leave the vacuum pump off and sealed if the vacuum pump pressure rise it means there is a leak