My AC stopped working and I called in contractor, He injected the dye in the refrigerant line, so he can find the location of the leak.

He added dye on May 22nd and also refilled refrigerant, AC started working. He told me that he will come back later and inspect with UV light to find the leak.

We did use AC at least for 10 hours (as per usage report from my thermostat) after that. He said that he will come back in August, but I am worried about all traces of leaked dye fading out and not being able to find its traces with UV light if we wait too long.

Does anybody know how much time I have to inspect the leak before all traces of dye are gone ? He is very busy guy. I don't want to bother him unless someone here tells me that I should act fast.

By the way, last year in June I had another contractor refilled refrigerant which worked entire summer of last year and I found in May of this year again that it is not working again.

  • 1
    IME the UV dye lingers. It's in the lubricant, so it doesn't really evaporate.
    – Huesmann
    Jun 11, 2023 at 12:38
  • 2
    You could buy or borrow a black light and have a look around. But indeed, the whole point of this method is that the dye accumulates where it leaks out, for later detection.
    – Ecnerwal
    Jun 11, 2023 at 12:57
  • 1
    The bigger worry is that the new refrigerant will all leak out before the contractor comes back. The dye is mixed in with the refrigerant/lubricant so will keep leaking out until then - you don't have to worry about not having fresh dye at the leak.
    – Armand
    Jun 11, 2023 at 18:54
  • Never used it but heard mention that a problem might be false positives from the last guy doing it (so, the reverse of your problem actually). "In small-to-medium sized systems, you can find leaks within minutes. In commercial systems, it may take a few hours for the dye to circulate completely. For preventative maintenance, add Spectroline dye long before you have a problem." - I don't think they plan on finding a leak.... Or did they at least try for 10m looking, or just say, sign here?
    – Mazura
    Jun 11, 2023 at 20:02
  • "he will come back in August" to actually do something about it. The right thing being you coughing up 10k on a new system, the wrong one: filling every year. Or that one thing everyone hopes is the problem: a leak in a system somewhere that's actually fixable. How long? Ideally before you fill it again next year.
    – Mazura
    Jun 11, 2023 at 20:12

1 Answer 1


According to my experienced AC guy when he added dye to my system with a very small leak ..

  • 10 hours is not enough. If ten hours was enough (bigger leak) he would have found it with his wand.
  • At least a few weeks of hot weather and regular use is required.
  • A few months is fine. He added it in May and the plan is to return in September. By then there will be plenty of dye around the area of the leak, and it's his low season.

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