Not unusual. Most AC systems are only designed to cool your home to about 20 degrees less than the outside temperature - so unless you have a particularly good building envelope (ie lots of insulation and very little air leakage) your AC unit is likely fighting a loosing battle during the worst heat waves.
When temperatures exceed 100 degrees Fahrenheit outside, setting your air conditioning (AC) to around 75-78 degrees Fahrenheit is generally considered efficient. Here are some reasons for this recommendation:
Clean your Air Filters, Vents, and Ducts – A clogged air filter will struggle to meet the thermostat's set temperature since the dirt and debris buildup prevents air from circulating through the vents. And as airflow into living spaces drops, so do comfort levels.
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.
When temperatures outside become higher than 100 degrees Fahrenheit, the air conditioning system can consume more energy and begin to malfunction or fail. Most air conditioning systems are designed to function with outside temperatures of 100 degrees or less.
It's true that air conditioners do have limits when the outside temperature is extreme. This means that your air conditioner may be able to keep your home at 77 or 78 degrees when it is 104 degrees outside.
Cooling a house from 80 to 72 degrees is a common goal for many, especially during the peak of summer. On average, this process takes roughly two and a half to three and a half hours.
Just because the outdoor temperature is above 100, the Ideal temperature to set your AC unit to doesn't change — it's 78 degrees. Higher temperatures in the home are to be expected when the weather is hotter than usual, but your thermostat can still be set the same as if it were a lower temperature outside.
On a 90-degree day, your AC system might need to run more frequently to maintain a comfortable indoor temperature. Typically, an AC unit should run for about 15-20 minutes per cycle.
How Often Do I Need to Change Out My Air Filter? Generally, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days, or 3 months. That can change based on where your home is located (ex. dusty, dry climates), if you have any pets, and the age of your system and equipment.
Leaking or Low Refrigerant
The most likely cause of this is a leak. A leak not only keeps the AC unit from cooling properly, but also it can cause other issues within the home. For example, when it isn't cool enough, humidity levels can rise in your home making it feel hotter than it is inside.
In extreme heat, you might notice your air conditioner isn't as effective, and your energy bills could be higher. Here's why: High temperatures put extra stress on the AC, which can lead to parts like fan motors and compressors getting too hot. This can cause uneven cooling or even damage the system.
When you spritz your condenser, you encourage it to evaporate the water, which helps it cool off more easily. It, therefore, needs to work less, which reduces the amount of energy it uses and the amount of burned energy you end up paying for in the long run.
Rochester Electric and Gas recommends setting your thermostat at 78 degrees or higher, as each degree above 75 degrees saves 3% of energy on cooling. A higher internal temperature actually slows heat flowing into your living space, so it saves additional money on air conditioning.
If it's 90 degrees outside, most people would set their AC to a perfectly comfortable temperature of 68-72°F.
Blocked Airflow
If your AC doesn't receive enough air, circulating cool air will take much longer throughout your home. Blockages can develop at several points in your HVAC system that lead to reduced output and longer cooling times.
Keep Your Cool
Close your window treatments during the day when the sun is out. Turn your ceiling fans in a counterclockwise direction. Doing so will create a literal wind-chill effect that should allow you to set your thermostat about 4 degrees higher than usual -- and you won't feel one bit warmer.
As long as you are staying comfortable, your home is reaching set thermostat temperature on very hot days and airflow from vents is normal, and your energy bills are about the same as they were last year – there's likely not a problem.
One possible reason your AC is not reaching the set temperature is that the thermostat could be dirty. If dirt, dust, or other debris has accumulated within the thermostat box, it can cause the wires to heat up or other issues. Thermostats are cleaned during routine HVAC maintenance to help prevent this from happening.
For instance, if it's 100 degrees outside, aim to set your thermostat to at least 80 degrees. Adhering to the 20-degree rule maintains energy efficiency, prevents strain on your cooling system, extends its lifespan, and promotes lower energy bills and consistent indoor comfort.
There are a number of reasons why your air conditioner might be running but not cooling. It could be an issue with the thermostat, the compressor, or the evaporator coils. Or, it could simply be clogged with dust and debris, which is preventing it from working properly.
If the temperature is set to 74°F but the thermometer shows 78°F, you will have to recalibrate the thermostat to account for this 4-degree deviation. Even with older AC units or furnaces, you might have to recalibrate your thermostat from time to time.