An AC that runs but doesn’t cool usually has an airflow restriction, a refrigerant charge problem, a heat-rejection issue at the outdoor unit, or a control/thermostat fault. The most common real-world cause is poor airflow from a clogged filter or a dirty indoor or outdoor coil that can’t move heat. After that, low refrigerant from a leak or a failing fan can keep the system from transferring heat even while it hums along. In our Las Vegas-area service, we often find outdoor coils packed with dust after windstorms, which makes the unit run longer with little cooling.
Check these simple items first:
- Replace a dirty air filter and clear supply/return vents.
- Set the thermostat to Cool and Auto; make sure temperatures aren’t in a setback mode.
- Rinse debris from the outdoor coil and keep 2–3 feet clear around it.
- Look for ice on refrigerant lines or water near the air handler.
Turn the system off if you see ice or hear hissing and schedule a diagnostic to prevent compressor damage.
Updated: 2026-09-09
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