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I intend to call a repair person, but I just want to make I've exhausted possibilities that don't involve messing with the refrigerant lines. The A/C was working yesterday with no problems (outdoor temp in the upper 90s), but today it started blowing room temperature air from the vents during the day (~85°F inside, outdoors again in the upper 90s), and same thing at night (~85°F inside when exterior temp was 70°F).

  • Outdoor condenser fan is operational
  • Thermostat is set to "Cool" and "Auto" fan (and there is no heat pump)
  • Outside unit is clean, free of debris, manufactured in 2004 (Duncan)
  • Indoor filter is pretty clean; no obvious air flow problems inside
  • Compressor turns on and heats up to an exterior temperature of ~130°F (perhaps hotter, it had not been on too long before I checked)
  • The larger, low-pressure, insulated line is very hot by the compressor (nearest 6 inches of pipes was ~115°F) and ambient temperature about 1 foot away from the compressor (~90°F); the smaller, high pressure line was also hot
  • There are no visible signs of leaking refrigerant; none of the pipes are cool, let alone freezing

Mostly I'm just surprised that it broke so suddenly, though everything I checked seems to be working. Any common wiring issues that are consistent with these symptoms? Or can bad compressors exhibit these symptoms?

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    The first thing is to have the pressures checked, a low Freon charge can go from working to not working as the temps increase. The small line if much hotter tells me that the compressor is working, with the larger suction line being fairly warm suggest the system is low on Freon and the system is working harder to cool. At this point I would use sub cooling and super heat to verify the charge and add if needed. Detecting a small leak can be difficult even with high end equipment sometimes the leak is small enough that no oil is apparent (a good indicator that there is a leak). Not a DIY job. – Ed Beal Jul 11 '18 at 15:28
  • sounds like a leak, but a hot return line indicates otherwise; you'll need an expert – dandavis Jul 11 '18 at 17:42
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If it quit cooling all of a sudden My best guess would be the compressor. To be more precise it is most probably the suction valve has broken. Either way the unit needs to be replaced.

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    Change the compressor or the entire condensing unit? – Jim Stewart Jul 11 '18 at 12:41
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It was the compressor capacitor. I don't really understand why the compressor was hot—I measured the temperature at night before and after running the A/C and it was about 30°F warmer after running it. I must be going crazy.

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