I had all my refrigerant leak out and a tech came and couldn't find a leak with Nitrogen. Also was able to pull an exceptionally deep vacuum @ 240 microns, which I hear would not go below 1000-1500 with even the smallest of holes along the system. Not having resolved the mystery how it had disappeared we thought it was a one-of and recharge the system but it all leaked out again after 2 weeks.

However, during both the Nitrogen test as well as vacuum pull, we didn't test the Schrader valves as the hose fitting were mounted the whole time. That leaves them out of the test, right? How likely is it for the Schrader valves to leak? Spraying soapy water did not show any leak.

  • It is possible for them to leak. If yours is leaking or not, I do not know. I have a tire on my truck that was leaking, The station took it off and checked it out and did not find anything, did have them replace the valve. it still had a slow leak. One time when filling it back up, I forgot to put the cap back on and lost it. The tire has been full/not leaking for months. Odd.
    – crip659
    Commented Jun 3, 2023 at 15:54
  • Have them do a dye test.
    – SteveSh
    Commented Jun 3, 2023 at 16:46
  • what is the device you are having issues with? A/C, heat pump, fridge, freezer? Commented Jun 3, 2023 at 17:25
  • central AC (air handler + condenser), AC only no heat
    – amphibient
    Commented Jun 3, 2023 at 17:34
  • 1
    I think you're reading too much into the vacuum indication. It's not particularly hard for fittings to resist vacuum. Pressure is only -15 PSI at most. Commented Jun 3, 2023 at 19:51

2 Answers 2


Answering "how likely" based on discussions with two exprienced technicians working on my system.

The valves can leak, but it is not likely, IE not either technician's natural suspicion. And it's easy to test if one of them is leaking. It is not likely to be the source of ongoing problems if you had a competent technician service the system.

Evasive leaks are usually pinholes in the evaporator and pressure and nitrogen testing are not always effective. The next step is injecting special UV dye into the system. You leave it for a few weeks (a few hot weather weeks), and then the leak is visible under UV light from the dye deposited all around it. It's a costly and time-consuming test. If the leak is in the Schrader valve, however unlikely, it will show up there too. Costly because it requires two visits by a not-junior experienced technician, and two sacrificial refills of the system.

  • I have seen them leak, mainly the ones that clamp on the tubing and puncher it.
    – Gil
    Commented Jun 3, 2023 at 16:27
  • would i be able to pull 240 mic vacuum if i had even the smallest pinhole leak in the coil?
    – amphibient
    Commented Jun 3, 2023 at 16:37
  • 1
    @amphibient I don't know and obviously I can't diagnose your system. I'm not an A/C technician, what I'm providing in my answer is the consistent "attitude" of two experienced ones, that a 1) a leaky Schrader valve is not something they would spend time on initially. That doesn't mean it can't leak. and 2) Some leaks are so hard to find that, too, is not worth spending time on ... at some point cut your losses and use dye.
    – jay613
    Commented Jun 3, 2023 at 16:47
  • I don't understand the "two sacrificial refills" part of your answer. When they dye tested my system, they just added the dye.
    – SteveSh
    Commented Jun 3, 2023 at 16:48
  • 2
    @SteveSh It's a leaky system. When they come to add the dye, it's empty. They fill it. When they come back to find the dye, it has lost some of the fill .. they can't repair it immediately (it needs parts and a different technician) so they fill it again ... then they repair it and refill it a third time. (It doesn't have to be that bad, but it can be.) Things that can make this process drag on for months (and hence you lose more refrigerant) are: 1) shortage of technicians so long periods between visits, and 2) if the leaky evaporator is under warranty.
    – jay613
    Commented Jun 3, 2023 at 16:51

I was just at a meeting for school maintenance managers in California where the Schrader valve was the main topic. Their fix was a simple valve cap! According to their extensive research and testing, that's the only place refrigerant leaks from the system. The cap stops it completely. You can buy a cap from online retailurs such as Amazon. If it's good enough for a CA government facility, it's good enough for you!

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