An AC that runs but doesn’t cool usually has restricted airflow, low refrigerant, a dirty or frozen coil, or a thermostat/duct issue. The most common cause is a clogged filter that chokes airflow and lets the indoor coil get too cold.
We service Colorado homes every day and often find wind-blown debris matting the outdoor coil so the system can’t dump heat. A quick visual check can save a service call, but warm air after basic steps points to a sealed‑system or electrical problem that needs a licensed tech. If the indoor blower runs but the outdoor fan sits still, the contactor or capacitor may be at fault.
Try these simple checks first:
- Replace a dirty air filter.
- Confirm the thermostat is set to Cool and Fan Auto, then lower the setpoint.
- Clear leaves from the outdoor unit and gently rinse the coil from inside out.
- Open supply and return vents; don’t block the furnace/air handler door.
Turn the system off and call a pro if you see ice on the refrigerant lines or water pooling at the furnace.
Updated: 2026-06-29
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