An AC that runs but doesn’t cool usually has an airflow restriction, a dirty outdoor coil, low refrigerant, or a control issue like an incorrect thermostat setting. The most common real cause is a clogged filter or blocked condenser that prevents heat from leaving your home. Even a thin dust layer on the outside coil can stop heat transfer while the unit sounds normal. On Castle Rock service calls, we often find a filter overdue for replacement or a coil matted with debris after windy weeks. If basic checks don’t help, professional diagnostics are best, and repairs can often be done the same day.
Try these quick checks before you call:
- Set thermostat to Cool, fan Auto, and lower the setpoint.
- Replace a dirty filter and open closed supply vents.
- Clear leaves/grass from the outdoor unit and straighten crushed fins.
- Look for ice on the refrigerant lines or repeated breaker trips.
If you see ice or smell burning, shut the AC off and call a technician to prevent damage.
Updated: 2026-09-18
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