AC Failure During a Montgomery County Heat Wave: Your First 5 Steps

Step 1: Check the Thermostat and Power

Start with the least expensive causes. Confirm the thermostat is set to Cool and the target is several degrees below the current room temperature, then replace the batteries even if the display looks normal. A weak battery can quietly drop the call for cooling.

Next, look at the electrical panel. Central air often has two breakers, one for the indoor air handler and one for the outdoor condenser. If a breaker has tripped, reset it once. If it trips again right away, stop and leave it off, because a breaker that keeps tripping is warning you of a real fault rather than a nuisance.

Step 2: Look at the Air Filter and Vents

A clogged air filter is one of the most common reasons an AC struggles or shuts down in a heat wave. When airflow is choked, the indoor coil can ice over and the system loses its ability to cool. Pull the filter and, if it is gray and packed, replace it.

Then make sure supply and return vents are open and unblocked by furniture or rugs. The system needs a clear path to move air, and closing off too many rooms actually works against you by starving the return.

Step 3: Check for a Frozen Coil

If the system runs but blows warm, or you see ice on the copper lines or the indoor unit, the coil has likely frozen. This is your cue to turn the system off at the thermostat and let it thaw fully, which can take a few hours, before running it again. Forcing a frozen system to keep running can damage the compressor, the most expensive part in the whole unit.

Running the fan on its own can speed the thaw. Once everything is clear and dry, a fresh filter and clean coils give the system its best chance of restarting normally. If it freezes again quickly, that points to low refrigerant or an airflow problem that needs a technician.

Step 4: Keep the House and People Cool

While you wait, actively fight the heat. A house that stays cooler is easier to bring back down once the AC is running, and staying ahead of heat stress matters most for the vulnerable.

• Close blinds and curtains on the sunny side of the house to block solar gain.
• Run ceiling and box fans to keep air moving, and open windows overnight if the outdoor air cools off.
• Hydrate steadily and check on elderly neighbors, young children, and pets, who handle heat poorly.
• If indoor temperatures climb dangerously, relocate to a cooling center, a library, or a mall until repairs are done.

Step 5: Know When to Call for Repair

If the basics did not restore cooling, or the system trips its breaker, blows warm, freezes repeatedly, or makes a hard buzzing or grinding noise, it is time for a professional. A failed capacitor, a burned-out condenser fan motor, a seized compressor, or a refrigerant leak all need measured diagnosis and the correct part, not a reset button.

Refrigerant work in particular is not a homeowner job, both because it requires EPA-certified handling and because a system low on refrigerant almost always has a leak that must be found and fixed, not just topped off. During a heat wave, response time matters, so call early rather than waiting to see if it fixes itself.

What Really Fails on an AC During a Heat Wave

After enough summers you learn that heat waves do not create new problems so much as expose the ones already there. The single most common failure we see on the hottest days is a run capacitor, a small cylindrical part that gives the compressor and fan motor the jolt they need to start. Heat degrades capacitors, so a marginal one that limped through June finally gives out in a July stretch, and the outdoor fan or compressor goes silent while the thermostat keeps calling.

Close behind are condenser fan motors that seize after years of sun and weather, contactors whose points burn and stick, and low refrigerant from a slow leak that leaves the coil starved and prone to freezing. We test the capacitor with a meter, check the contactor and motor amp draw, and read the refrigerant pressures against the outdoor temperature before touching a part. That last point matters: on a 90-degree afternoon the correct pressures differ from a mild day, and topping off refrigerant without finding the leak just delays the same failure. A leak search and a proper repair beat a summer of gradual re-charges.