What Those AC Noises Mean: A Troubleshooting Guide

Your air conditioner shouldn't sound like a construction site. While some operational noise is normal, unusual sounds often indicate problems that need attention. Here's your guide to AC noises and what they mean.

Normal AC Sounds

Before we discuss problems, know that these sounds are typically normal: gentle humming from the outdoor unit, soft whooshing of air through vents, clicking when the system starts or stops, and a quiet hum from the indoor unit.

Sounds That Signal Problems

Banging or Clanking

What it means: Usually indicates a loose or broken part inside the compressor, such as a connecting rod, piston pin, or crankshaft.

What to do: Turn off the system and call for service. Running with loose parts causes more damage.

Squealing or Screeching

What it means: Often a belt issue in older systems, or a failing motor bearing in newer units. Could also indicate high internal pressure.

What to do: If it's brief at startup, monitor it. If persistent or getting worse, call for service.

Grinding

What it means: Motor bearings are failing or there's a serious mechanical problem.

What to do: Turn off the system immediately and call for repair.

Buzzing

What it means: Could indicate loose parts, debris in the unit, dirty condenser coils, loose fan blades, refrigerant leak, or failing contactor relay.

What to do: Have it inspected—the cause could be minor or serious.

Hissing

What it means: Likely a refrigerant leak, which is serious. Could also be high compressor pressure or a leaky expansion valve.

What to do: Call for service promptly. Refrigerant leaks affect performance and can damage the compressor.

Clicking (Repeated)

What it means: While startup/shutdown clicks are normal, constant clicking suggests an electrical issue—possibly a failing thermostat or defective control.

What to do: Don't ignore electrical issues. Call for inspection.