Why Your AC Cannot Reach 68 Degrees When It Is 100 Degrees Outside (And Why That Is Normal)

Aug 7th 2026

It is the hottest week of the year. The asphalt is melting, the sun is punishing, and you just want your living room to feel like a walk in refrigerator. You walk up to the thermostat, crank it down to 68 degrees, and wait.

Four hours later, the system is still roaring, but the thermostat is completely stuck at 78 degrees. Panic sets in. You assume your air conditioner is broken, and you start mentally preparing to pay a massive repair bill.

Take a deep breath. Your air conditioner is probably not broken at all. It is simply bound by the laws of physics. Here is the hard truth about extreme heat, and why demanding 68 degrees in the middle of a heatwave is a recipe for disaster.

The 20 Degree Rule

To understand why your living room is warm, you have to understand a concept called the temperature differential. In the HVAC industry, this is known as Delta T.

Residential air conditioning systems are not designed to create magic winter wonderlands. They are engineered to cool your home by approximately 20 degrees from the outside temperature. That means if it is 100 degrees in your backyard, an indoor temperature of 80 degrees is actually a sign of a perfectly functioning system.

Your air conditioner does not create cold air. It removes heat from the air inside your home and pumps it outside. When the outside air is scorching, the machinery simply hits a thermal limit. It cannot physically move the heat fast enough to overcome a 30 or 40 degree difference.

What Happens When You Demand the Impossible

If you set your thermostat to 68 degrees on a 100 degree day, your AC will never reach the target. Because it cannot hit the target, it will never shut off. This creates a dangerous chain reaction for your equipment.

The Energy Bill Spike: Running a heavy compressor for ten hours straight is incredibly expensive. Your utility bill will skyrocket, but your comfort level will not change at all.
The Frozen Coil Disaster: An overworked AC running constantly without a break will often freeze its indoor coils into a solid block of ice. Once it freezes, it stops cooling completely, leaving you blowing warm air around a hot house.
The Motor Burnout: Forcing a machine to run at maximum capacity for days on end dramatically shortens its lifespan. You are risking a thousand dollar compressor replacement just to chase a temperature you will never reach.

How to Survive the Heat Wave

You cannot change the weather, and you cannot break the laws of physics. But you can hack your home to feel significantly cooler than the thermostat says it is.

The Strategy	How It Works	The Result
Block the Greenhouse Effect	Close all blinds and blackout curtains on your south and west facing windows.	Stops radiant heat from baking your floors and furniture.
Use the Wind Chill	Turn on your ceiling fans and make sure they are spinning counterclockwise.	Creates a breeze that evaporates sweat, making your skin feel up to four degrees cooler.
Change the Air Filter	Put a brand new, clean filter into your system.	Maximizes airflow, allowing your struggling AC to push as much conditioned air as possible.
Avoid the Oven	Do not cook dinner on the stove or in the oven. Grill outside or eat cold meals.	Prevents you from adding hundreds of degrees of unnecessary heat into your kitchen.

The Bottom Line

When the forecast predicts triple digit heat, it is time to adjust your expectations. Nudge your thermostat up to 78 degrees, turn on a fan, and let your air conditioner do its job at a sustainable pace.

Stop fighting the weather. Your system is working exactly as hard as it can, and giving it a realistic goal is the absolute best way to protect your home and your wallet. Let FiltersDelivered.com help keep your family cool by keeping the airflow of your HVAC system at its highest level. With great pricing and fast free shipping, we got you covered!