A single leak detection method that locates every leak in every situation does not exist. So, what determines which method is most accurate for different air-conditioning and refrigeration systems?
Leak Detection MethodsA thorough understanding of the common leak detection methods is necessary to select the one best for your process.
Bubble Solutions. The oldest method of leak detection, a soapy solution is applied at suspected leak points, usually with a squeeze bottle, brush or dauber. Escaping refrigerant causes bubbles to develop.
Halide Torches. Halide torches are considered a step up from bubble solutions. However, they reveal only a limited number of leaking refrigerants. The leak detection method is based on the fact that the torch's flame will turn green when exposed to refrigerants containing chlorine atoms (CFCs and HCFCs). Not all refrigerants contain chlorine atoms.
Electronic Detectors (Sniffers). Two basic types of electronic detectors are used to test for escaping refrigerant: heated diode and corona suppression.
Heated diode technology consists of a ceramic element that heats refrigerant and breaks apart the molecules, leaving positively charged chlorine or fluorine ions that are attracted to a negatively charged center collection wire. The flow of chlorine or fluorine ions to the center collection wire creates a small current. As the refrigerant concentration between the electrodes increases, current increases to a level that sets off an audio-visual alarm.
Corona suppression technology measures variations in the conductivity of gases passing between two electrodes. The instrument creates a high voltage DC spark that jumps from one point to another in the sensor, establishing a baseline current between the two points. A drop in current between the two points indicates the presence of an insulating gas. The greater the current drop, the higher the concentration of gas.
Ultrasonic Detectors. Using highly sensitive microphones, these AC- or battery-powered devices listen for the high pitched, inaudible sound of a leak that, when detected, sets off an audio-visual alarm.
Fluorescent Leak Detection. In this leak detection method, fluorescent dye is added to the air-conditioning or refrigeration system. Dye mixes with the lubricant and circulates with the refrigerant throughout the system. Where refrigerant leaks out, so does the dye. The refrigerant will evaporate, but the dye will remain at each leak site. When the air-conditioning or refrigeration system is scanned with an ultraviolet or UV/blue light lamp, the dye glows a bright yellow-green color, pinpointing the exact leak location.
With the fluorescent leak detection method, contractors should use an OEM-approved dye that is compatible with the system's lubricant. Also, it is best to select an ultraviolet or UV/blue light lamp that produces high intensity output. The greater the light intensity, the brighter the dye will glow, making it easier to find leaks.
Overall, when selecting a leak detection method, technicians must consider system, environmental and human factors. A ratings summary for five leak detection methods and the system, environmental and human factors that affect each method appear in table 1.
System FactorsThe type of refrigerant being used is important when choosing a leak detection method. Not all detectors work well with all types of refrigerants. Also, system size and configuration must be considered. There are tremendous differences among a small refrigerator unit, a medium-sized food processing plant refrigeration system and a large industrial system running on ammonia.
Large systems are more likely to develop multiple leaks, possibly hundreds of feet apart. In a small unit, multiple leaks are more likely to be next to one another, but every leak still must be precisely located.
Whatever the system size, its configuration can make finding leaks difficult. In a small unit, tight space limitations may make the job difficult. In a large system, personnel may need to be lifted to reach piping in the ceiling. Personnel also must check behind walls and around other barriers.
Accuracy, leak size and number of leaks also are system factors. A good leak detector should be able to pinpoint virtually every leak, regardless of size. In an indoor system, a large leak can raise refrigerant concentration in the air high enough to set off an area monitor or electronic sniffer. By then, it may not be possible to find the exact source of a leak. In addition, small leaks can be masked by larger ones and may be missed until a larger leak is repaired and the system is reinspected.
When facing the situation of multiple leaks, consider what should be done if a leak is indicated in an area where there are several leak sites in close proximity. Will a large leak hide smaller leaks from detection until after the large one is repaired? Will the detector clearly identify two or more leaks that are close to each other?
When a leak cannot be located but one obviously exists, the system may have an intermittent leak. It may be apparent under some conditions but not others. This can be a hit-or-miss proposition with most detection methods because the refrigerant may not be leaking at the moment it is being monitored.
Environmental FactorsWind and air currents affect the accuracy of electronic detectors and halide torches, which depend on sampling and testing the air in the vicinity of leaks. In outdoor systems, wind or occasional breezes can lead to a missed leak or a false alarm. Wind also can wreak havoc with bubble solutions.
Indoors, ventilation fans and convection currents lead to similar problems. Air currents may be eliminated by shutting down fans, but convection currents can disrupt readings and cause problems.
Ambient light can wash out the response of visual detectors such as fluorescent leak detectors and halide torches, making leaks difficult or impossible to see. Ultraviolet and UV/blue light lamps will help minimize this problem.
Ambient sound, other than that caused by leaks, obviously will affect ultrasonic detectors. Noisy environments such as parallel-rack refrigeration systems can fool this type of detector. Gas flowing through a pressure-regulating valve sounds similar to a leak. Some contractors claim that unrelated sounds such as crickets chirping can set off an ultrasonic leak detector.
Other gases, especially those that contain chlorine, can produce false positive readings from electronic air sampling/testing detectors. Chlorine-containing gases can emanate from urethane insulation, hydrocarbon-based solvents and other sources.
Human FactorsEase of use and maintenance are important considerations. Most detectors are relatively easy to use. Bubble solutions are the most basic method; the most difficult method is the electronic detector, which requires calibration and, on some models, switching sensitivities. Experience is the best teacher for finding leaks, but the easier a leak detection method is to use and maintain, the better the chances are of pinpointing leaks quickly and accurately.
Training requirements vary from method to method. Decide whether a detection method requires special knowledge or experience and use a leak detection method that provides the desired level of accuracy with a minimum amount of training.
Due to the high costs of refrigerants, equipment repair and the time and effort needed to locate leaks, proper preventive maintenance of air-conditioning and refrigeration systems is essential. Select a leak detection method that pinpoints leaks quickly and accurately so refrigerant losses are kept at a minimum. Often, by finding and repairing a minor leak early, headaches can be avoided later.