AC Noise Diagnosis — 10 Common Sounds
Cause: Loose or broken component inside the compressor, or a loose fan blade hitting the housing.
Action: Shut system off. Call immediately. Running with this noise can destroy your compressor.
Cause: Worn or failed motor bearings in the blower motor or condenser fan motor. Metal-on-metal contact.
Action: Shut off and call. Motor replacement needed before it seizes completely.
Cause: Failing blower motor belt (older units) or a blower wheel that needs lubrication. Also: refrigerant overpressure.
Action: Don't ignore — call same day before it escalates to full motor failure.
Cause: Loose parts vibrating, failing electrical components (capacitor/contactor), refrigerant leak, or debris in the outdoor unit.
Action: Diagnose quickly — electrical buzzing can be a fire hazard.
Cause: Normal thermal expansion and contraction of ductwork and housing components as temperature changes.
Action: Normal — no action needed unless clicking is constant or happens mid-cycle.
Cause: Failed capacitor or bad contactor preventing the system from starting. Compressor trying and failing repeatedly.
Action: Turn system off to prevent compressor damage. Call us — capacitor/contactor replacement is typically same-day.
Cause: Refrigerant leak (high-pitched hiss) or air duct leaks (lower hiss). Refrigerant leaks worsen over time.
Action: Hissing from refrigerant lines = call HVAC immediately. From vents = ductwork inspection.
Cause: Refrigerant leak causing bubbling in the line, or water in the condensate drain causing gurgling sounds.
Action: Refrigerant bubbling requires leak repair. Drain gurgling requires drain cleaning.
Cause: Loose screws or panels on the unit, debris (leaves, sticks) caught in the outdoor unit, or loose ductwork.
Action: Check outdoor unit for debris first. If rattling continues, schedule a diagnostic.
Cause: Outdoor unit humming but not running = failed capacitor or contactor. Compressor attempting to start but can't.
Action: Turn system to FAN ONLY to prevent compressor damage. Call us for same-day capacitor/contactor replacement.
When to Shut Off Your AC Immediately
- • Loud banging or clanking (loose/broken internal component)
- • Metal-on-metal grinding (bearing failure)
- • Constant clicking that won't start (compressor protection)
- • Humming outdoor unit with no cooling (capacitor failure, compressor at risk)
- • Any noise accompanied by a burning smell
Continuing to run the system with these symptoms can turn a $300 repair into a $2,500 compressor replacement.
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