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Our AC stops emitting cold air on very hot days (100+). It recovers after about 1h of not running. The condenser fan keeps running, but the compressor switches off. I only recently caught it as it was switching the compressor off while running, it makes a distinctive noise before apparently some overload switch stops the compressor entirely, I catured the noise on video.

I'm sure something around the compressor, coolant, compressor itself is broken but I have no idea what to expect; does anyone have any further ideas for triage?

  • That short capture is some what useless , it could be a high pressure or low pressure shutdown , an over charge is common with high pressure and a low charge is more often with low pressure. Icing of the inside can happen in both cases depending on the type of control into the evaporator I can keep up double speak but high temps and over charge with a bypass would be my first guess. – Ed Beal Sep 7 at 0:53
  • @EdBeal What would be useful to capture, a longer clip or something else specific? Thanks! – Henrik Mühe Sep 7 at 4:05
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To me it sounds like a over charge but this is really hard to detect, based on your description that it works correctly except on the hottest days.

Everything works great for a month then on a day that is a few degrees hotter a high pressure bypass kicks in (high squeal). if you shut it down and let it cool down it runs ok , or if you spray the outside coils with water it runs ok. (A possible trouble shooting test.)

I have only seen this a few times but the high pitch squeal on very hot days may be a safety (high pressure bypass possibly) . If this is the cause the system starts and sounds normal but then the high pitch squeal kicks in and no cooling I have found this when the high pressure is over 400 psi. Most recently when I found this I Cooled the system down and it’s normal pressures were ~325. The only difference I could figure out was a few degrees higher ambient temp. Recovered a few ounces of refrigerant and the problem of low cooling went away but I found the problem by checking super heat and sub cooling pressure and temp checks something beyond DIY in many countries because of license requirements.

If the system sounds normal then the squeal, over charge may be the root cause based on your description and the short recording this would be my best guess with your description.

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