Few things are worse than an air conditioner that runs but does not actually cool your home, especially during a New York City heat wave. Before you panic and call for emergency service, there are several common causes you can check and potentially fix yourself. From a dirty filter restricting airflow to a tripped breaker cutting power to the outdoor unit, many AC cooling failures have simple solutions. This troubleshooting guide walks you through the most likely causes in order from simplest to most complex, helping you either resolve the issue yourself or provide useful diagnostic information to your technician.
Verify the thermostat is set to cool mode and the temperature is set below the current room temperature. Check that the fan is set to auto rather than on, as the on setting blows air continuously even when the compressor is not running.
A severely clogged filter can restrict airflow enough to prevent effective cooling. Remove the filter and check it. If it is gray or matted or you cannot see light through it, replace it immediately and run the system for 30 minutes.
Go outside and verify the condenser unit is running. The fan should be spinning and you should feel warm air blowing upward. If the unit is not running, check the disconnect switch near the unit and the circuit breaker in your electrical panel.
Open the access panel on the indoor unit and look for ice on the evaporator coil. If frozen, turn the system to fan only mode for two to three hours to let it thaw completely. Ice on the coil prevents heat absorption.
A clogged condensate drain can trigger a safety switch that shuts down the cooling function. Locate the drain line, usually a PVC pipe near the indoor unit, and check for blockages. Pour a cup of white vinegar through the line to clear minor clogs.
If the outdoor unit will not start after resetting the breaker, the evaporator coil keeps freezing after thawing, or supply air temperature is not at least 15 degrees below room temperature, call a licensed HVAC technician.
Call (646) 439-4057This often indicates a refrigerant leak, a failing compressor, or a dirty evaporator coil that intermittently ices over. Have a technician inspect the system to identify the root cause.
Yes. A severely clogged filter restricts airflow across the evaporator coil. With insufficient air, the coil gets too cold, freezes over, and cooling stops entirely until the ice melts.
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