Refrigerant Leaks and a Fluorescent Green Bigfoot

“I was hot on its trail and felt sure that I would find it lurking around the next corner, I was on the track of the ever elusive refrigerant leak!”


This is what it's like listening to some technicians lament about refrigerant leaks they can’t locate. The tale above may be an exaggeration, but it’s not far off the mark; you’d think they were looking for Bigfoot instead of a refrigerant leak.


Before we go much further let’s get something straight; there’s no such thing as a refrigerant leak that can’t be found. If you can’t find it, you’re either not trying hard enough or you haven’t learned the tricks for finding small, pesky leaks.

When a technician describes his efforts to find a leak there is one statement that tells me he doesn’t know how to leak check, “I even used fluorescent dye” When I hear that, I cringe.


I tried fluorescent dye once, and I’ll never use it again. I added the die as the instructions indicated, then waited three days before returning. I arrived at the job around dusk, plugged in the black light, and couldn’t believe my eyes.


Everything was glowing green; there were green hand-prints on the unit, green boot prints in the grass, and half the tools in my bag were glowing green. It looked like a B rated monster movie about space aliens...minus the aliens. Yea, I found the leak, but I could have found it without the die if I had tried.


Finding a refrigerant leak is easy. The process starts with when the symptoms of the leak are noticed. This simple bit of information can narrow your search considerably; in the winter the system is off, the pressure on the high and low side are equal, and the pressures are lower due to the cold ambient temperatures. In the summer the condenser and liquid line pressures are much higher than the low side pressures.


What does this mean to you? If the system held its charge through the winter months, but lost it during the summer, there is a good chance it’s a high side leak. If it lost the charge over the winter, but holds it through the cooling season, it’s likely a low side leak.


Will this information pinpoint the leak for you? No, but it can narrow your search considerably. Does the above logic always prove true? Not always, but often enough to be useful.


The next step is simply looking for signs of a leak. Oil is a sure indication of a leak. After looking for signs of oil it’s time to break out a quality electronic leak detector. If you don’t own one, or the one you own is, shall we say, cheap; do the following-

  1. Stop reading this.

  2. Purchase a high quality leak detector.

  3. Continue reading this.

Here’s a quick tip for buying a leak detector; spend more money than you think you should spend, any less and it’s not a quality unit. Unlike many of the tools you own, you will be using this almost daily during the cooling season, so it’s worth the money.


Refrigerant is heavier than air, remember this and use it to your advantage. If you suspect a leak in the indoor coil, place the detection probe in the drain pan; that is where the refrigerant will collect.


If you think the leak is in the outdoor section but can’t pinpoint it, try the following- Install gauges on the system, disable the condenser fan. Turn on the unit and allow the head pressure to rise slightly higher than normal, then shut the system down. Now, quickly scan the coil headers, coil end plates, and fin pack with the leak detector.


Typical trouble spots for small nuisance leaks are; the condenser coil end sheets, condenser fin pack, fusible plugs, service valve stems, any mechanical connections, and the indoor coil.


To summarize;

  • You need a quality leak detector.

  • Refrigerant is heavier than air, check low points with your leak detector.

  • Systems that hold charge during the cooling season, but leak out over the winter, normally are leaking on the low side.

  • Systems that hold charge during the winter, but leak out during the cooling season normally have high side leaks.

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