Fluorescent Leak Detection: Shedding Light and Saving Money

The latest results from the Residential Energy Consumption Survey (RECS) show that 87 percent of U.S. households (that’s 100 million homes) are now equipped with air conditioning. Air conditioners use about 5% of all the electricity produced in the United States, at an annual cost of more than $11 billion to homeowners. Fluorescent leak detection could make that cost decrease significantly.

                   outside air conditionerseveral air conditioners outside of a building

With so many of us spending so much money to keep our families, homes and businesses cool, it’s important to keep air conditioners running properly. Because even the best built and most expensive air conditioners and refrigeration units will eventually leak.

Have you searched for a leak in an air conditioning or refrigeration system recently?

Most likely you used a bubble solution. A time honored, albeit old-fashioned procedure, the bubble solution is the most familiar method of leak detection in the HVAC industry.

Just spray a solution of soapy water over a suspected leak surface until you see some tiny bubbles appear. Wherever you see bubbles, that’s where your leak is.

Sounds great, right?

Maybe…for the tire on your son’s first two-wheeler bicycle…or the inflatable pool toy your daughter plays with. But as an answer for accurately and consistently locating and repairing air conditioning and refrigeration leaks… the “bubble solution” isn’t really much of a solution at all.

Because while this technique might seem cost efficient up front…nothing but the cost of a little soapy water and a spray bottle…in the long run, its lack of accuracy and consistency ends up costing you much more than you think.

That’s because the hit-or-mostly-miss method requires:

– Multiple service callbacks

– High refrigerant replacement costs

Furthermore, once the technician arrives, the bubble solution spraying routine keeps them on the job for an excessive amount of time. That’s because the “soapy bubble” leak detection method is not sensitive enough to find smaller leaks…especially on outdoors units located in breezy areas. What’s worse, as the bubbles dry up, you have to remember where the leak was while you move on to locate possibly additional leak sources.

Because if you don’t remember where the bubbles appeared, then you have to go back and re-spray the areas you just sprayed and searched all over again…and again…until every leak has finally been identified, located and fixed.

By spraying that much soap and water everywhere you’re likely to do more to wash the outside of your system then find the leaks within it.

So if you want to save Mr. Bubbles for tub time, what’s the alternative?

The F, F, Cs of a Preventive Maintenance Plan

By implementing a regularly scheduled “Preventive Maintenance Plan” you can reduce the likelihood of having to fix large, costly leaks and pay for major repairs to your air conditioner or refrigeration systems. At its best, a preventive maintenance plan will tell you there are no leaks in your system. At its worst… and in many instances, especially in older systems… you will discover the presence not of just a single leak but multiple leak sources. Enacting a preventive maintenance plan is as simple as A, B, C. Well actually F, F, C.




Preventive maintenance plans have many benefits for the owner, technician and the environment.

    • They are easily implemented
    • They reduce contract service costs
    • They decrease the need for call backs
    • They lower contract server costs
    • They are an ideal means for cutting emissions

Professionals looking for a reliable way to implement successful preventive maintenance plans and pinpoint numerous leak locations are increasingly relying on fluorescent leak detection.

What is Fluorescent Leak Detection?

Dating back to 1,500 B.C., the Chinese were writing on the subject of natural fluorescence they observed in glowworms and fireflies. But it wasn’t until 1852 that modern scientific method was applied to fluorescence by Sir George Stokes. Stokes Law of Fluorescence basically says that, the wavelength of fluorescence emission must be greater than that of the exciting radiation. If you recall the feeling the first time you ever saw fluorescent object glow as child, you can understand why it is sometimes referred to as the “wow” effect.

uv/violet light diagram

a) Dye absorbs UV/Violet light energy, gets excited

b) Dye emits energy as green glow, gets grounded.

Today, there are numerous applications of the “wow effect” in everyday life. Like microscopic technology, X-ray imaging, and radio waves, the practical application of fluorescent technology products allows us to see a huge array of phenomena not perceptible to the naked eye. The enhanced capabilities that fluorescent technology provides allows us to better access, manage and respond to issues that were previously only known when they reached heightened conditions, or after time consuming traditional inspection techniques.

HVAC/R fluorescent leak detection then is a method in which a small amount of fluorescent dye is introduced into and circulated through a cooling system. The combined dye and refrigerant mixture will seek the lowest points of pressure and thus accumulate at all leak sites.

technician performing fluorescent leak detection

A leak detection lamp (a light source that illuminates the dye) can then be used to quickly inspect the system for leaks during regular maintenance or service calls. If a leak is present, a sustained fluorescent glow (usually green) will appear making even the smallest holes easy to pinpoint.

leak detection lamp

Since fluorescent leak detection is a line-of-sight maintenance technique, you need to be able to see the inspection sight. For tight spots, you can bounce the violet light off an inspection mirror. Some mirrors are telescopic and even come with built-in detection lamps.

violet light bouncing off inspection mirror

Now that the leaks how been FOUND and permanently identified they can be easily FIXED without having to hunt them down again.

Fluorescent dyes need to have the systems they service be on and running in order for the dye to circulate through the entire system. That’s why they are most useful when added as part of a preventive maintenance plan, before a potential problem arises.

Good Dyes vs. Bad Dyes

You have to be careful. Just like there are good guys and bad guys in the world, there are good and bad dyes. And unless you educate yourself, it can be just as difficult to discern the differences between the two.

A quality fluorescent dye is:

  • Co-Solvent Free

Co-solvent based dyes can impair the properties of the systems lubricant, resulting in diminished viscosity and lubricity. Co-solvent free dyes don’t degrade lubricants or cause systems to run sluggish.

Most dye manufacturers formulate their dye with a solvent called Aromatic 200. Its viscosity is detrimental to the operating parameters of refrigeration oil. Another solvent used by some dye manufacturers is NMP, or N-menthylpyrrolidone. NMP is known to be detrimental to aluminum, light metals, rubbers, and plastics.

What’s worse, both Aromatic 200 and NMP are listed in the Pesticide Action Network (PAN) as Bad Actor Pesticides because of their reproductive or development toxicity, or carcinogenicity. Not exactly the kind of chemicals you want circulating through the rooms of your home or in close proximity to refrigerated foods.


Every system has oil and refrigerant charge capacity limits recommended by the manufacturer. Some dyes are so diluted that the amount of dye required for leaks to be detected can overload the system and causing them to function way below optimum performance levels.

Approved by Industry Leaders

According to AC/R equipment manufacturers, the majority of dyes on the market will void the warranties if added. A quality fluorescent dye that is OEM-Approved will not void equipment warranties. The best ones are also NSF Certified, which means they meet food-grade processing requirements for category codes HTX-2 and HX-2.

Dyes that meet all these requirements can stay and work in your system indefinitely. So any time you do an inspection that finds a leak, always remember to thoroughly CLEAN the dye from the leak source after you have repaired the problem. That way you won’t be confused the next time you look for leaks with your detection lamp.

There is no one method of leak detection that is 100% fool-proof every time. All techniques have their strengths and limitations. But by adopting a preventive maintenance plan and applying the F, F, C’s of fluorescent leak detection to your AC/R system, you will save time, effort, and money over the life of your equipment.

For more information about flueorescent leak detection for your HVAC/R system, please go to Spectroline.

By: Paul Perillie, marketing content specialist for Spectronics Corporation

Spectronics Corporation is the world’s leading manufacturer of ultraviolet equipment and fluorescent materials. These state-of-the-art products are built to exacting engineering standards and are utilized for literally hundreds of markets and applications that demand uncompromising quality and reliability. Spectroline® UV lamps and radiometers are widely used to verify the structural integrity of military and commercial aircraft. Spectroline® fluorescent dyes are used to check for fluid leaks in power plants, nuclear reactors, oil pipelines and industrial facilities worldwide, and were even used on the U.S. Space Shuttle. A Nobel Prize-winning scientist used Spectroline® UV crosslinkers and transilluminators to do groundbreaking electrophoresis research that will benefit mankind as part of the Human Genome Project.


Residential Energy Consumption Survey


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