Why Is My AC Making Noise? Sounds and Causes

What each sound usually means

• Buzzing or humming at the outdoor unit while the fan does not spin: usually a failing capacitor or contactor
• Clicking that repeats at start-up: a relay, contactor or weak capacitor struggling to start the system
• Rattling or vibration: a loose panel or screw, debris in the fan, or the refrigerant lines touching the wall
• Squealing or screeching: worn bearings in the blower or outdoor fan motor
• Hissing or bubbling: possibly a refrigerant leak, which needs a technician
• Gurgling or dripping inside: a drain line that is partly blocked and close to overflowing
• Banging or grinding: a loose or broken part inside the fan or compressor

Check these first (safe for anyone)

• Look at the air filter; a very dirty filter makes the system work harder and louder
• With the power off at the outdoor disconnect, remove leaves and branches from around the unit
• Make sure the access panels on the indoor unit are closed and seated
• Confirm the thermostat is set to Cool and the fan setting is on Auto

Turn the AC off and call if

• You smell burning or see smoke
• You hear banging or grinding
• The outdoor unit buzzes but the fan does not turn; running it like this can overheat the motor or compressor
• The breaker trips again after you reset it once

What it usually costs

Most noises come from parts that are inexpensive to replace early. In Miami-Dade, a capacitor or contactor is typically $225 to $450 and a fan or blower motor $650 to $1,450. The AirWise visit and diagnostic is $89, and it is free if you approve the repair.

Need help with this?

When the air conditioner stops cooling, we find the cause, show you the readings, and give you a clear price before any repair begins. Service in English and Spanish.