Quick answer
What you should know first
Confirm that the thermostat is set to Cool with the temperature below room temperature, check the filter and supply airflow, verify that the indoor and outdoor equipment have power, and look for ice or water around the system. Turn the system off and call for service if the coil is frozen, the breaker trips again, the outdoor fan or compressor will not run, or the system blows room-temperature air continuously.
Step by step
Safe checks and practical next steps
Check the thermostat mode and setpoint
Make sure the thermostat is set to Cool rather than Fan or Heat, and set the temperature several degrees below the room temperature. If Fan is set to On, the blower may circulate room-temperature air between cooling cycles; Auto is normally the better test setting.
Check the filter and open supply registers
Replace a visibly dirty filter with the correct size and make sure the main supply and return openings are not blocked. Restricted airflow can reduce cooling and may freeze the evaporator coil. Do not run the system with the filter removed as a permanent solution.
Look for ice before continuing
Ice on the refrigerant line, indoor coil cabinet, or outdoor unit is not normal cooling operation. Turn cooling off and set the fan to On only if the blower is operating normally, then arrange service. Do not chip the ice or pour hot water on equipment.
Verify power without repeatedly resetting breakers
The indoor blower and outdoor condenser usually have separate power sources. Check the labeled breakers and the indoor service switch. A breaker that trips again is a warning, not a reset routine—leave it off and call for diagnosis.
Observe the outdoor unit from a safe distance
When cooling is called, listen and look for the outdoor fan and compressor. Do not remove panels or reach through the grille. A humming unit, a stopped fan, rapid starts and stops, or silence while the indoor blower runs points to an electrical, control, or equipment problem that needs service.
Check for a full drain pan or condensate safety switch
Some systems shut off the outdoor unit when a drain backs up. Visible water in an emergency pan, a full condensate pump, or water around the air handler should be addressed before more damage occurs. Do not bypass a safety switch.
Stop and call for service
Bring in an HVAC professional when:
- There is ice on the coil or refrigerant tubing.
- The outdoor unit hums, the fan does not turn, or the compressor repeatedly tries to start.
- A breaker trips more than once or there is a burning smell.
- Water is overflowing, a drain safety has opened, or the ceiling below the unit is wet.
- The system runs continuously but cannot lower the indoor temperature.
Common follow-up questions
A little more clarity
Should I add refrigerant if the AC is not cooling?
No. Refrigerant level must be diagnosed with the correct instruments, and a low charge usually means a leak or another problem. Adding refrigerant without finding the cause is not a safe homeowner repair.
Why is the indoor fan running when the outdoor unit is off?
Possible causes include thermostat fan settings, a condensate safety switch, lost outdoor power, a failed capacitor or contactor, control wiring, or an outdoor-unit fault. A technician can test the complete call sequence safely.
This guide provides general information, not instructions for every HVAC model or installation. Follow the manual for your exact equipment and applicable New Jersey requirements. When in doubt, stop and call a qualified professional.