Symptoms
- Compressor and fan run nonstop, never reaching a pause
- House may or may not be reaching the set temperature
- Higher than usual energy bills
Likely causes
- CommonExtreme outdoor heat pushing the system to its limitOn the hottest days, continuous running to barely keep up is normal for many systems.
- CommonLow refrigerant reducing cooling capacityA system low on refrigerant has to run longer to produce the same amount of cooling.
- CommonDirty filter or coil restricting performanceReduced airflow or heat exchange makes the system work harder and longer.
- PossibleThermostat set unrealistically lowA setpoint far below what's achievable outdoors will keep the system running indefinitely.
- PossibleUndersized system for the houseA system too small for the home's cooling load will run nonstop trying to keep up.
What to do
- Check the thermostat setpoint is realistic, generally no more than 20 degrees below outdoor temperature.
- Replace the filter and clean the outdoor coil if either looks dirty.
- Check the indoor coil for ice, which points to airflow or refrigerant issues.
- Monitor whether the system ever cycles off overnight or during cooler parts of the day; if it never does even then, that's a stronger sign of an underlying issue.
- If it's an extreme heat day and the system is otherwise well maintained, some continuous running is expected.
- Call a technician for a refrigerant and capacity check if constant running happens even in moderate weather.
Tools and parts
- Garden hose
AC air filterSearch: “central air filter size replacement”
When to call a pro
Call an HVAC technician if the system runs constantly even in moderate weather; refrigerant level or system sizing may need addressing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.