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Air conditioner making a loud noise
A new noise is the system telling you something changed. Which noise it is narrows the cause a great deal.
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The short version
- Most likely cause
- A loose panel, debris in the fan or a worn part.
- Safe to check
- Whether something is touching the outdoor fan, with the power off.
- Call a technician when
- You hear banging, grinding, screeching or hissing.
Safe to check yourself
- Note when the sound happens: at start, while running or at shutdown.
- Look for sticks or leaves in the outdoor unit with the power off.
- Check that the unit sits level on its pad.
- Check that access panels are screwed down.
Switch off and call
- Banging or clanking from the outdoor unit.
- Metal-on-metal grinding or screeching.
- Loud buzzing with the fan not turning.
- Hissing, with or without ice on the lines.
What the sounds usually mean
- Buzzing or hummingOften electrical: a failing capacitor or contactor, or a motor that is trying to start and cannot.
- Banging or clankingA loose or broken part inside the compressor or fan. Running the system can make the damage worse.
- Squealing or grindingWorn motor bearings in the outdoor fan or the indoor blower.
- Hissing or bubblingCan point to a refrigerant leak, which needs finding and repairing, not topping up.
What a technician will do
- Listen to the system start, run and stop.
- Inspect the fan, motor and compressor mounts.
- Test the capacitor and contactor.
- Check the refrigerant charge if a leak is suspected.
Always cut power at the outdoor disconnect before reaching into the unit. The fan can start without warning.
Related guides
What an AC capacitor replacement costs, and why
AC compressor replacement: repair or replace the systemSources
- US Department of Energy
- US Environmental Protection Agency: R-22 phaseout