Plain-language explanation: This page is educational and does not replace testing the actual equipment.
Start with the thermostat
Confirm the thermostat is set to cooling, the setpoint is below room temperature, and the fan is not set to ON when the compressor is off.
Check the outdoor unit
If the indoor blower runs but the outdoor unit is silent, electrical, capacitor, contactor, control, or safety problems may be involved.
Airflow and freezing
A dirty filter or blower problem can lead to poor airflow and a frozen evaporator coil.
Refrigeration problems
Low refrigerant, compressor problems, restrictions, or a failed metering device can reduce cooling.
Frequently asked questions
Can a dirty filter make the AC blow warm air?
Yes. Severe airflow restriction can cause poor cooling or coil icing.
Should I reset the breaker?
A single reset may be reasonable if you know which breaker serves the system, but repeated trips require service.
Can I keep running it?
If the system is frozen, making loud noises, or tripping electrical protection, turn it off and request service.