Trends in Refrigeration-Leak Detection
Learn about six common techniques for leak-checking R-410A systems; brazing errors and how to avoid them; and a tip to check for a leaking refrigerant-access port valve.
Publication date: May 2012
Leak detection is more important today than in any other era of air-conditioning and refrigeration because of R-410A’s emergence as a preferred HFC refrigerant and replacement to R-22. Finding and eliminating leaks in R-410A systems is important because of its near-azeotropic characteristics. R-410A consists of R-32 and R-125, the former of which has the potential to escape more freely from a leak hole because its molecules are smaller.
Whether its due to copper sources, R-410A’s higher pressures, POE oil’s affinity for moisture, the proliferation of household volatile organic compounds that attack copper coils, or brazing craftsmanship at the manufacturing and service-technician level, leaks are more prevalent and intermittent than before.
Anyone doubting refrigeration leaks are on the rise need to look no further than Grant’s Air Conditioning and Heating in Visalia, CA, which recently reported in an HVAC trade magazine that they experienced a 40% rise in coil replacement on a variety of R-410A central A/C brands. Surprisingly, these units were less than two years in operation, according to Service Manager Mike Tanner, a NATE-certified, 17-year-veteran of HVACR service.
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.
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.
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.
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.
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.
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.
Paul Appler is the Director of Research for Cliplight Manufacturing Co. located in Toronto, ON, Canada. A frequent speaker for NATE and RSES, Appler is the inventor of a leak sealant for HVAC systems. Appler can be reached at 866-548-3644 or firstname.lastname@example.org. For more information, visit www.cliplight.com.