What Do My HVAC Noises Mean?
Most HVAC noises map to a specific failure. Screeching and grinding are the two that mean shut the system off now, because both indicate metal-on-metal contact in a motor bearing. Buzzing, clicking and banging are less urgent but still worth diagnosing before they become a replacement.
Shut it off for these two
- Screeching or squealing — usually a blower or fan motor bearing failing, or a seized motor
- Grinding — metal on metal inside a motor, which will destroy the motor if it keeps running
Book a visit for these
- Buzzing at the outdoor unit — often a failing capacitor or a contactor that is not pulling in cleanly
- Repeated clicking at startup — a relay or control trying and failing to close
- Banging or clanking — a loose blower wheel or a broken motor mount
- Rattling panels — sometimes only loose screws, which is worth checking before you book
Noises that are normal
A soft whoosh at startup, a gentle click from the thermostat, and light expansion ticking in the ductwork are all normal. So is a brief change in pitch as a variable-speed blower ramps. Normal sounds are steady and repeatable; failure sounds are new, sharp, or getting worse.
Common questions
Why is my AC screeching?
Screeching usually means a blower or fan motor bearing is failing, or the motor is seizing. Shut the system off and have it looked at before the motor is destroyed.
Why does my outdoor unit buzz?
A buzz at the condenser is often a failing run capacitor or a contactor that is not closing cleanly. Both are common wear parts and are usually a straightforward repair.
Which HVAC noises are normal?
A soft whoosh at startup, a light click from the thermostat, and mild expansion ticking in ducts are normal. Sharp, new, or worsening sounds are not.
Reviewed by Briton Davis, owner, and the Cool Guys Home Services service team · Licensed, bonded & insured (CSLB #1156890)
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Why Does My Breaker Trip When the AC Runs?
A breaker doing its job. Why you should stop resetting it and what is usually wrong.
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