AC Not Cooling: A Homeowner Checklist

Set the mode to COOL, the fan to AUTO, and the setpoint at least three degrees below the current room reading. If the display is blank or dim, replace the batteries before anything else.

On heat pumps, make sure the system is not on EMERGENCY HEAT, which some thermostats label AUX.

Pull the filter and hold it up to a light. If light barely passes through, it is restricting airflow enough to affect cooling and can eventually freeze the coil.

Look at the breaker panel for the indoor and outdoor circuits. Reset a tripped breaker once. If it trips again, leave it off — repeated trips indicate a real electrical fault.

Also look for a light-switch style service switch near the indoor unit, which sometimes gets turned off during other work.

Open every supply register and clear furniture, rugs, and boxes away from return grilles. Closing vents in unused rooms does not save energy and often makes cooling worse.

The fan should be spinning and the air leaving the top should feel warm. A humming unit with a stationary fan usually points to a failed capacitor — shut it off rather than letting it keep straining.

Clear grass clippings, pine straw, and shrubs to leave at least two feet of clearance.

Ice on the copper suction line or indoor coil means shutting cooling off and running the fan to thaw. Water in the drain pan or the emergency pan points to a drainage problem.

Do not open electrical compartments, handle refrigerant, bypass safety devices, or attempt electrical repairs unless you are properly qualified. Capacitors can hold a charge even with power off.