Air conditioners make predictable sounds: a startup click, a steady outdoor hum, a soft rush of air indoors, and a whoosh when a heat pump changes modes. New or changed sounds are worth paying attention to, and a few of them warrant shutting the system off.
Use this as a translation guide, then describe what you hear in your own words when you call.
Humming with no start
A steady hum at the outdoor unit while nothing spins commonly points to a failed start component such as a capacitor, or a compressor that cannot start. Continuing to let it try can add damage, so switching the system off is reasonable while you arrange help.
Repeated clicking
A hard click every few minutes can mean the system is attempting to start and something is interrupting it — a control, relay, or protective device. Occasional clicks at cycle start and stop are normal.
Screeching or squealing
High-pitched noise often comes from a motor bearing or, on older equipment, a belt. It typically gets worse over weeks rather than failing instantly, but it should not be ignored.
Grinding or metal-on-metal
This suggests a bearing failure or something contacting the fan blade. Shut the system off; continued operation can turn a repair into a replacement.
Banging or clanking
Loose hardware, a fan blade out of balance, or internal compressor damage produce heavy, irregular noise. Debris that fell into the outdoor cabinet is another possibility.
Hissing or bubbling
Hissing may indicate a refrigerant leak or a metering-device restriction. Bubbling near the indoor unit sometimes accompanies low charge. Both are worth reporting specifically.
Rattling, buzzing panels, and duct noise
Loose panels, vibrating electrical hardware, or duct expansion can produce noise without meaning failure. Still, describe it — a rattle that started recently may be a symptom.
- Note where the sound comes from: outdoor unit, indoor unit, or vents
- Note when it occurs: startup, shutdown, or continuously
- Note whether it is new, worsening, or long-standing
- Record a short phone video if the sound is intermittent
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