Various Abnormal Noises During Operation

Question

Accepted Answer

Clicking / metallic bang — faulty start capacitor or foreign object hitting fan blade. Check: Power off, visually inspect fan blade for foreign objects (leaves, plastic, wire). Measure capacitor capacitance with LCR meter (>±6% deviation = faulty). What to do: 1) Remove foreign object, restart. 2) Replace capacitor if faulty (same specs). Always check for blade damage — damaged blade leads to vibration and secondary bearing failure. Squealing / screeching — worn fan bearing or belt slipping. Check: Manually rotate fan shaft with motor off — stiffness, rattling, or roughness indicates bearing failure. Belt-drive units: check belt slack (10–15mm deflection when pressed) and check for cracks. What to do: Replace bearing: confirm spec (e.g., 6202, 6203) then replace. Use proper bearing press tool — no hammer direct strike (damages race). Belt slip: adjust tension or replace belt. Thumping / vibration — internal compressor damage or loose mounting bolts. Check: 1) Check mounting bolt torque (if loose when hand-shaken, tighten immediately). 2) Measure vibration with vibration meter or phone app — above 10 mm/s requires compressor inspection. 3) Measure compressor running current — above 120% of rated suggests internal failure. What to do: Loose bolts: re-tighten to spec torque + check anti-vibration rubber (replace if hardened). Compressor noise: stop immediately → record low/high pressure and running current, then decide on replacement. Compressor replacement requires refrigerant recovery and recharge. Hissing / bubbling — refrigerant leak or flashing. Check: Scan pipe connections and indoor unit area with electronic leak detector. Apply soapy water to flare joints and check for bubbles. Confirm operating low-side pressure with gauge — lower than normal suggests leak. What to do: After locating leak: 1) Flare joint → re-flare or re-torque with torque wrench. 2) Brazed joint → re-braze. 3) Core pin leak → sealant or coil replacement. After repair: nitrogen pressure test (1.5 MPa, 24h) → vacuum → refrigerant charge. Rattling — loose panel or foreign object ingestion. Check: During operation, press each panel area by hand and check if noise changes. Disassemble and inspect for foreign objects. Check outdoor unit intake and fan guard interior. What to do: Re-tighten panel screws (until no play when hand-shaken). Remove foreign objects. For repeated loosening from vibration, apply thread-locking adhesive (Loctite 243, etc.).

Various Abnormal Noises During Operation

Likely causes

Clicking / metallic bang — faulty start capacitor or foreign object hitting fan blade

Squealing / screeching — worn fan bearing or belt slipping

Thumping / vibration — internal compressor damage or loose mounting bolts

Hissing / bubbling — refrigerant leak or flashing

Rattling — loose panel or foreign object ingestion

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