What should my AC be set at if its 90 degrees outside?

Author: Prof. Cassandre Hilpert MD  |  Last update: Monday, December 29, 2025

If the outdoor temperature is 90 degrees, it's recommended to set your thermostat between 75-78 degrees. This setting strikes a balance between comfort and energy efficiency. Lowering the thermostat setting too much can cause the AC to run continuously, leading to higher electricity bills and more frequent repairs.

How cool should my house be if it's 90 outside?

Some of the basics include: turn your thermostat up a couple degrees and deal with 76 to 78 degree temperatures indoors for a few days. close off unused rooms. close doors and vents.

How long should an AC unit run in 90 degree weather?

On moderately warm days, your AC may need to cycle on and off approximately every 15 minutes to keep the temperature steady. This means the AC might run for 15-20 minutes, turn off, and then start again after a short break to maintain comfort.

Is 72 a good temperature for air conditioning?

Setting your air conditioning to 72°F is generally considered a comfortable indoor temperature for many people. It strikes a good balance between comfort and energy efficiency, making it a popular choice for residential settings.

Do you need AC in 90 degree weather?

In 90-degree weather, understanding how long an air conditioner run should be is crucial for maintaining optimal indoor comfort. When the temperature outside reaches a scorching 90 degrees, your air conditioner (AC) becomes an essential tool for maintaining a comfortable indoor temperature.

AC Temperature Setting and Display

Is 40 psi too much for AC?

Like your engine oil dipstick, your air conditioning system does not have a set level. There is a range of low-side and high-side pressures that are acceptable and vary depending on the ambient temperature. However, generally your low-side pressure should be 30 to 40 PSI and high-side pressure should be 150 to 175 PSI.

What should I set my AC to on a hot day?

Summer Air Conditioner Settings

In the summer, experts say the thermostat for your air conditioner should be set to at least 78°F during the day when people are at home.

Does keeping the AC at 72 save money?

Best AC Temperature Settings While You Are Home

As you consider the most comfortable room temperature for your lifestyle and family, keep in mind that for each degree that you set your thermostat above 72 degrees, you can save up to 3% on your energy bill.

Why is my AC set to 72 but reads 78?

Clean the Thermostat

Sometimes, when the room temperature doesn't match the thermostat setting, the problem could be dirt buildup on its interior parts. A dirt coating around the inner components may create excess heat and cause the thermostat to give the wrong readings.

Is it normal for my AC to run all day in the summer?

Here's the thing: It's normal for your AC to run continuously during hot summer months. You see, on extremely hot days—we're talkin' high 90s to 100s—your system needs to keep up with the incoming heat. To do that, it will run longer in order to maintain a constant, desired temperature in your home.

How long should it take to cool a house from 90 to 72?

Most central air conditioners can cool a moderate-sized (3 to 4 bedroom) home by about 5 degrees every 3 hours. This means while it can take no more than a couple hours to lower the temperature to a comfortable range in the fall or autumn, it can take much longer in the summer.

What temperature does AC work best?

The Ideal Temperature for Maintaining Your Air Conditioning

Minimize frequent cycling (turning on and off) to reduce stress on AC unit components. It is recommended to set the thermostat setting between 65–80°F for optimal performance and to keep those cooling bills minimal.

Why won't my AC go below 74?

Your AC might not cool properly due to thermostat issues, an undersized unit, or extremely high outdoor temps—so check those first. Keep an eye on airflow—replace clogged filters every 3 months, and make sure vents and ducts aren't blocked for efficient cooling.

What temp should my house be if it's 100 outside?

During heat waves, experts, including utility companies, recommend keeping your thermostat no more than 20 degrees cooler than the outdoor temperature. For instance, if it's 100 degrees outside, aim to set your thermostat to at least 80 degrees.

What should you keep your AC on to save money?

You'll save more money on air conditioning bills the closer you keep your inside temperature to the outside temperature, so see if you can stand to set your thermostat at 78 instead of 72.

What should I set my AC to at night?

Recommended AC Temperature for Sleeping

The Sleep Foundation says 65° is the best temperature for sleeping. However, if you prefer a slightly warmer or cooler room, that's okay, too. The recommended range is 60–68°, so there is some wiggle room.

How cool should my house be if it's 110 outside?

For many of us, 70 degrees is the ideal indoor temperature, but when it is close to 100 degrees outside, your AC unit will be working quite hard to meet these expectations. Consider setting your thermostat at 75 degrees to 80 degrees in your home if the outside temperature is approaching triple digits.

Which AC mode to use in summer?

When you activate dry mode, the fan on your AC is set to a higher speed, which helps circulate and draw moisture out of the air. Dry mode is especially useful during humid seasons such as summertime, when you may find yourself fighting against high levels of humidity in your home.

What is the coolest number for AC?

Setting your AC to 16°C will cool the room more than setting it to 30°C. However, keep in mind that extremely low temperatures can lead to higher energy consumption and may not be comfortable for occupants. A moderate setting, like around 22–24°C, is often recommended for both comfort and efficiency.

Should AC be on auto or on?

There are benefits to having your air conditioner set to “auto” and “on.” The benefits of the “auto” setting include higher efficiency, lower energy bills, better humidity control, less wear and tear on some components, and quieter running.

Is 72 a good temperature for air conditioning at night?

The National Sleep Foundation says 60-67 is a good temperature for sleep, but that might be too cold for you and increase your cooling bill. As a compromise, 70-plus degrees is a good setting.

What is the best pressure for AC?

Turn on the air conditioner and observe the pressure readings, which should be between 30-40 PSI for most systems (though some may require higher or lower pressures).

Is 37 PSI too low?

Tire pressure has a significant impact on your vehicle's performance. If it gets too low, your safety—and the safety of others on the road—is impacted. Hence, maintaining the correct tire pressure (between 32 to 35 PSI is a good idea. Remember, anything lower than 20 PSI is considered a flat tire.

What happens if your AC has too much pressure?

Burnout of the Air Conditioner Compressor Motor: Excess refrigerant can also leak into the crankcase and mix with the oil, causing the crankcase pressure to rise. This added stress can burn out the compressor motor, making it inoperable. As a result, you may have to replace the whole cooling system.

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