Troubleshooting

Confirm the thermostat is set to Cool below room temperature, check that the air filter isn't clogged, and make sure the outdoor unit is running and free of ice. A frosted coil means you should turn the system off and let it thaw before calling for service.

Squealing often points to a worn blower belt or motor bearing. Banging or clanking usually means a loose part inside the cabinet. Occasional clicking on startup is normal, but repeated clicking without the system starting usually signals a failed capacitor.

Check batteries first if it's a battery-powered model, then check the breaker for your air handler or furnace. A tripped breaker is the most common cause of a completely dead thermostat.

Low refrigerant, a dirty air filter, or a failing blower motor are the most common causes. Turn the system off and let it fully thaw for a few hours before running it again — operating an iced unit can damage the compressor.

This is called short-cycling, and it's usually caused by a dirty filter, low refrigerant, an oversized system, or a failing thermostat sensor. It wastes energy and wears out components faster, so it should be checked soon.