When your AC fails, "what do AC" refers to the set of diagnostic and corrective actions needed to restore cooling function. This includes checking power supply, airflow, thermostat settings, refrigerant levels, and mechanical components. Prompt response prevents damage and reduces downtime.
AC systems rely on a closed-loop refrigeration cycle involving compressors, condensers, evaporators, and expansion valves. When any component malfunctions, cooling stops. Common triggers include tripped breakers, dirty filters, low refrigerant, or faulty thermostats. Identifying the root cause quickly improves efficiency and safety.
According to the U.S. Department of Energy, 70% of HVAC failures stem from poor maintenance or simple oversight-like blocked vents or neglected filter changes. A well-maintained system operates 15-20% more efficiently and lasts longer than one ignored for years.
An AC cools indoor air by transferring heat from inside to outside. The process begins when the thermostat signals the system to run. The compressor pressurizes refrigerant gas, turning it into a hot liquid. This flows through the condenser coil outside, releasing heat into the atmosphere.
The cooled liquid then passes through an expansion valve, reducing pressure and temperature. As it enters the indoor evaporator coil, it absorbs heat from the surrounding air. A blower fan pushes warm indoor air over the cold coil, cooling it before returning it to the room.
Once the refrigerant absorbs heat, it returns to the compressor as a low-pressure gas, restarting the cycle. This loop runs continuously until the thermostat reaches the desired temperature.
Most AC issues fall into four categories: electrical, airflow, refrigerant, and mechanical failure. Each requires specific checks and actions.
If your AC is frozen, turn off the system and let it thaw for 4-6 hours. Running a frozen unit damages the compressor. After thawing, inspect the blower motor and ductwork for obstructions. A clogged return vent can starve the system of air.
I once encountered a home where the AC froze within 30 minutes of startup. The issue was a collapsed duct behind a closet wall. Airflow restriction caused the evaporator coil to drop below freezing. Replacing the damaged section restored normal operation.
Different failure modes produce distinct symptoms. Recognizing them speeds up diagnosis.
| Failure Type | Signs | Immediate Action |
|---|---|---|
| Electrical | No power, clicking sounds, burning smell | Turn off power at the breaker. Call an electrician. |
| Airflow | Warm air, ice on coils, weak airflow | Replace filter. Clear vents. Check blower wheel. |
| Refrigerant | Weak cooling, hissing noise, puddles under unit | Shut down system. Contact a licensed technician. |
| Thermostat | System won't start, incorrect readings | Replace batteries. Reset to cooling mode. |
Freezing is a red flag. The EPA notes that improper refrigerant charge causes 40% of freeze-ups. Overcharging leads to high pressure and low temperatures in the evaporator. Undercharging causes poor heat absorption and uneven cooling.
Many assume AC problems are always complex or require full replacement. That's false. Most issues stem from simple, fixable causes. For example, a dirty filter can reduce efficiency by up to 15%, according to the National Association of Home Builders.
Another misconception: turning the thermostat to "cool" mode automatically starts the system. Some models require the fan setting to be set to "auto" or "on." If set to "on," the fan runs constantly, which can circulate dust and dry out air.
Also, AC units don't "run out" of coolness. They move heat. The cooling effect depends on proper airflow, correct refrigerant charge, and consistent power. If the system cycles on and off rapidly-called short-cycling-it may indicate a sensor fault or oversized equipment.
Do not attempt refrigerant handling unless certified. The Environmental Protection Agency prohibits unlicensed individuals from recovering or charging refrigerant. Violations carry fines up to $37,500 per incident.
If the system runs but doesn't cool, or if you hear grinding, squealing, or loud banging noises, stop using it. These indicate compressor or motor failure. Continuing operation risks permanent damage.
For persistent issues, consult a licensed HVAC technician. They'll perform a full system check: measure refrigerant pressure, test electrical circuits, inspect ductwork, and verify thermostat accuracy.
Knowing what to do when your AC fails keeps homes comfortable and avoids unnecessary costs. Addressing small issues early prevents major breakdowns.