My AC Stopped Working in the Heat — What Do I Do First?

Published: May 2, 2026 · By SAVA HVAC & Appliance Repair

Do these four things immediately: check the thermostat, check the breaker, check the air filter, and check that the outdoor unit has power. If none of those fix it, call a technician — don't keep cycling the system on and off, which can cause compressor damage.

Step 1: Check the Thermostat Settings First

This sounds obvious, but thermostat issues cause a surprising number of "AC failure" calls. Verify:

• It's set to COOL, not HEAT or FAN ONLY.
• The set temperature is below the current room temperature.
• If it's a battery-powered thermostat, replace the batteries. A low-battery thermostat can behave erratically or show incorrect readings.
• If you have a smart thermostat, check whether it lost its Wi-Fi connection or received an incorrect schedule update.

Step 2: Check the Circuit Breaker

Air conditioners draw significant current—especially during startup and on hot days when they're running hard. A tripped breaker is one of the most common causes of sudden AC shutdown.

Go to your electrical panel and look for the AC breaker (usually labeled "AC," "Air Handler," or "Condenser"). If it's tripped, it will be in the middle position—neither fully ON nor fully OFF. Reset it by flipping it fully OFF first, then back to ON.

Important: if the breaker trips again within minutes of resetting, stop. A repeatedly tripping breaker signals an electrical fault—a failing capacitor, an overloaded compressor, or a wiring issue. Resetting it repeatedly can damage the compressor or create a fire hazard. Call a technician.

Step 3: Check the Air Filter

A severely clogged air filter restricts airflow to the point where the evaporator coil freezes over. When the coil freezes, the system shuts down as a safety measure. This is more common than most people realize — especially in homes that haven't changed their filter in several months.

Pull the filter and hold it up to light. If you can't see light through it, it's overdue for replacement. Replace it, then turn the system to FAN ONLY for 1–2 hours to thaw the coil before switching back to COOL. Running a frozen coil in cooling mode can damage the compressor.

Step 4: Check the Outdoor Unit

Go outside and look at your condenser unit (the large box outside your home):

• Is the fan spinning? If the system has power but the fan isn't running, the condenser fan motor or capacitor may have failed.
• Is there a disconnect switch nearby? Most outdoor units have a small box on the wall nearby — it should be in the ON position.
• Is the unit covered in ice or frost? This confirms a frozen coil or refrigerant issue. Switch to FAN ONLY and call for service.
• Is it making unusual noises? Grinding, rattling, or a loud hum without the fan running are signs of component failure.

While You Wait for the Technician: Heat Safety Steps

The CDC reports that heat is the #1 weather-related killer in the United States, responsible for more deaths than hurricanes, tornadoes, and floods combined. According to the National Weather Service, a heat index of 103°F or higher creates conditions where heat exhaustion is likely and heat stroke is possible with prolonged exposure. While you wait for repair, take these steps:

• Close blinds and curtains on south and west-facing windows to block solar heat gain.
• Use ceiling fans — they won't cool the air, but the wind-chill effect makes temperatures feel 4–6°F lower.
• Go low. Hot air rises. The coolest part of your home is the ground floor or basement.
• Stay hydrated. Drink water regularly even if you don't feel thirsty.
• If indoor temps exceed 90°F — especially for elderly residents, young children, or anyone with a medical condition — move to a cooling center, a neighbor's home, a library, or a mall.

What NOT to Do When Your AC Stops Working

• Don't keep switching the system on and off trying to force it to start. Short-cycling stresses the compressor and can turn a minor repair into a major one.
• Don't reset the breaker more than once if it trips repeatedly — this masks a real electrical problem.
• Don't add refrigerant yourself. Under EPA Section 608 of the Clean Air Act, refrigerant handling requires EPA certification. The U.S. Environmental Protection Agency states that technicians who purchase and handle refrigerants must be certified under Section 608 — DIY refrigerant kits are unsafe and ineffective for most central AC systems.
• Don't ignore ice on the unit. A frozen coil needs to fully thaw before the system runs — running it frozen can destroy the compressor.

According to ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers), residential cooling systems are designed to maintain comfort within defined temperature and humidity parameters — when a system fails during extreme heat, restoring operation quickly is not just a comfort issue but a health and safety priority, particularly for vulnerable occupants.

Frequently Asked Questions