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My central air is set at 74. Yesterday and today, the house was up to 80. It has been very hot outside(90). Would this affect my ac unit?

  • Are you asking if extreme heat will make it more difficult to cool your home, or if the heat will damage the AC system itself? – BMitch Jul 20 '15 at 23:24
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    Air Conditioner Can't Keep up – Mazura Jul 20 '15 at 23:36
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    Is the outdoor unit running? Touch the pipes that are connected to the unit with your hand. One (smaller) should be warm, the other (larger) should be cool and possibly wet. My first guess would be low refrigerant due to a leak. An HVAC technician will be able to test for low refrigerant. – Tester101 Jul 21 '15 at 2:38
  • I know old post - but yes outside temp does affect the unit efficiency and hence ability to cool - if it is 120-130 degrees out the efficiency drops big time. However in your situation your AC unit has an issue that needs to be checked out. No one can give you a magic bullet answer with out details as there are lots of reasons it might not work correctly if it ever did. – Ken Jul 29 '17 at 9:52
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Assuming the question is why can't your AC keep your home cooler, there are several possibilities:

  • The AC is low on refrigerant, look for a temperature difference of 14-20°F between the return and vents to see if the unit is cooling efficiently. If you're low, you will likely need to call a professional to pressurize the system and check for any leaks.
  • Dirty air filters. These should be changed at least twice a year depending on the air quality, though many manufacturers will suggest monthly.
  • Frozen coils. This is a sign of low refrigerant pressure, dirty filters, running the AC when it's too cold out, or having an AC that's over-sized for the home. When this happens, airflow will stop, and you'll need to turnoff the AC to defrost the coils and correct the cause.
  • Insufficient insulation, especially in the attic or older single pane windows. I would look for problem areas using an IR thermometer. If you add insulation on top of existing insulation, make sure you don't have two vapor barriers (craft paper backing on the fiberglass rolls) and consider installing it perpendicular to the existing insulation to minimize gaps.
  • Insufficient weather stripping around windows, doors, chimneys, or any other openings. Worst case you can feel these, see light showing through the crack, or notice them with the IR thermometer. But for more thorough testing, you'd have a blower installed in a door to create a vacuum and use a smoke test.

As for whether running the AC when it can't keep up with the demand will damage it, only if it's low on refrigerant since that contains a lubricating oil. When the refrigerant gets too low, the compressor will typically fail to turn on to protect from damaging itself. Otherwise it's just standard wear and tear.

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iLikeDirt is wrong. If your air conditioner cannot cool your house to 74 when the outside temperature is 90, then something is wrong. Either the air conditioner is undersized or it not working properly. You should check the air filters and air vents but you may need to call in a specialist to check the unit itself. My units have kept my house at 74 with outside temperatures over 100 and even that should not tax a properly designed unit that is operating correctly.

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    I think both you and @iLikeDirt are correct. It could be the AC itself, the inefficiencies of the house, or both. – mjohns Jul 21 '15 at 1:08
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Your AC unit is fine. YOU on the other hand, might be feeling a bit toasty. Looks like you need more attic insulation and a radiant barrier.

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