Start with the thermostat and power
Confirm the thermostat is set to cooling and the set temperature is below the indoor temperature. If the system is not running at all, check whether the relevant breaker has tripped. Do not repeatedly reset a breaker that continues to trip; that can indicate an electrical problem that needs professional evaluation.
Check the air filter and airflow
A heavily loaded filter can restrict airflow. ENERGY STAR recommends inspecting, cleaning, or changing filters regularly because dirty filters can raise energy use and contribute to equipment problems. If you replace a filter, use the size and type intended for the system.
Look for useful symptoms, not a self-diagnosis
Write down whether the air is warm, airflow is weak, the outdoor unit is running, the system is cycling on and off, or ice is visible on accessible components. Different faults can create similar symptoms, so this information is more useful than guessing which part failed.
Know when to stop checking
If you notice repeated breaker trips, burning odors, unusual electrical sounds, significant water leakage, or frozen components, stop operating the system and arrange an appropriate professional evaluation. Refrigerant and internal electrical work are not DIY tasks.
What to tell the service provider
- When the problem started
- Whether airflow is normal or weak
- Whether the outdoor unit is running
- Any visible ice, water, error code, or unusual noise
- Whether the breaker has tripped
For service options, see our central AC repair page.