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?
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.
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.