Fix it
Why is my AC blowing warm air?
Warm air from a running AC means the indoor half is moving air the outdoor half is not cooling. The split between "indoor works, outdoor does not" sorts almost every cause.
What it usually is
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The outdoor unit is not running at all
A tripped breaker, failed capacitor or seized condenser fan leaves the compressor idle while the indoor blower keeps circulating. Stand by the outdoor unit: silence, or a hum without the fan spinning, is your answer.
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Low refrigerant from a leak
Undercharge shows as long runs with feeble cooling, sometimes with ice on the small copper line. The refrigerant does not get used up — if it is low, it leaked, and the leak is the repair.
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A filthy filter or iced coil choking airflow
Weak, slightly-cool airflow rather than warm air, often after weeks of a neglected filter. Ice on the indoor coil confirms it.
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Thermostat or mode mix-ups
FAN set to ON circulates unconditioned air between cycles; a reversed heat-pump setting or a dead thermostat battery does the rest. The simplest fixes on the list, always worth the first minute.
What you can check yourself
Verify COOL mode, setpoint below room temperature, fan on AUTO. Replace the filter. At the outdoor unit, confirm the fan spins and the top of the unit blows warm exhaust — that is heat leaving your house, a good sign. A humming, non-spinning fan sometimes has a failed capacitor; leave that repair to a meter.
When it’s a job for a pro
Capacitors, charge diagnosis and leak repair are gauge work. If the coil ices repeatedly on a clean filter, stop running it — melting and refreezing just floods the pan while the real cause waits.
Capacitor replacement typically runs $150 to $400; leak diagnosis and repair $300 to $1,000; a thermostat battery costs pocket change and solves more calls than anyone admits.
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