I had a problem with with my AC window unit days ago. It kept doing a high deep sound while the sun is up. I had this same problem last year. Last year when I called the technician he told me the unit needed refrigerant. He fixed the problem and the unit ran for a year without issues.

This year the same problem happened, so I called my technician and he was not available. So, I called another technician and he told me that he sealed an open pipe leaking refrigerant, replaced something he referred to as automatic (he said it was under the control panel knobs), and filled the refrigerant.

After receiving the unit, I have noticed this hissing sound while the AC unit is cooling. It is continuous with 1-2 seconds intermissions. The technician told me it was normal and it was the compressor working.

I have had this unit for years now. I have never heard this sound, before. I also did not have this hissing sound before this year's "repair" which was days ago. The unit cools the room without that loud annoying sound it did before. Though, the hissing sound is driving me crazy. I cannot focus nor sleep. I think I will have a breakdown.

I hope you guys help me resolve this issue. What could have this technician done to introduce this sound? Is it possible the "automatic" thing he installed is causing this? Did maybe some air get inside while he was filling the refrigerant?

Thanks for any information you can give me.

Edit: Before the repair, I could hear this sound for around 3-4 seconds after shutting down the unit only. Though now I hear it for more than 10 seconds, after shutting the unit.

1 Answer 1


The noise could be coming from the refrigerant charge being incorrect. you did not say how old this A/C is but at some point these units are not cost effective to fix.

  • Thank you so much for taking the time to reply to my question. I really appreciate it. Can you tell me more about this? Can I ask another technician to release the current refrigerant and recharge it again to fix this hissing sound? The AC unit is old but I do not have money to replace it.
    – Rick James
    Commented Apr 12, 2020 at 15:16
  • Did you get the chance to see my comment. Thanks.
    – Rick James
    Commented Apr 14, 2020 at 18:20
  • Yeah, or it's the noise it's finally supposed to make because it's actually charged. Speaking of charging, how can you afford a guy to come out to your house but not a new/used window unit? The 'point which these units are not cost effective to fix' is always. I've installed almost a 100 hvac systems, so I know how to do it and have all the tools, but the only thing I fix on window units is bad gfci cord ends.
    – Mazura
    Commented May 13, 2020 at 7:52

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