Fridge No-Cool Noise: Buzz vs Click vs Hum Failure-Mode Tree

Why this matters

When a refrigerator stops cooling, the sound it makes at the compressor is a direct readout of where the start circuit failed. A buzz, a repeating click, and a steady hum each point to a different fault in the start-relay/overload/compressor chain. Reading the sound saves a teardown: a click-hum-pause cycle is the classic overload-trip pattern, a steady hum with no start is often a stalled compressor or weak start device, and a buzz can be a relay or a mounting/fan resonance. Pinning the sound to the right component, before condemning a compressor, avoids the most expensive wrong call in the trade.

Symptom presentation

A repeating click-then-hum-then-silence on a roughly two-to-five-minute cycle is the compressor trying to start, drawing locked-rotor current, and tripping its overload (the click is the overload opening and reclosing). A steady hum that never resolves into a running compressor points at a stalled compressor or a start device that is not phasing in the start winding. A buzz or rattle without a cooling failure can be a loose relay, a fan blade striking ice, or a vibrating line, but a buzz with no cooling points back at the start circuit. Note the rhythm and whether cooling is actually lost.

The interval between attempts is itself a clue. The overload is a thermal device, so it needs time to cool before it recloses; the few-minute cadence of click-hum-silence is the thermal recovery time of that overload, and it confirms the compressor is repeatedly attempting and failing to start under high current. A hum with no periodic silence means the overload is not tripping yet, so the compressor is energized but locked or the start winding is never dropping in. Timing the cycle separates an overload-protected start failure from a steady-state stall.

Quick checks

• Confirm the no-cool is real: read both compartment temps and feel whether the compressor dome is warm (trying to run) or cold (not energizing at all).
• Listen for the rhythm. A click-hum-silence cycle every few minutes is overload trips; a constant hum that never resolves is a stall; an intermittent buzz may be mechanical or a chattering relay.
• Pull the compressor electrical cover and inspect the start relay and overload for melting, discoloration, or an internal rattle in a PTC device.
• Check the condenser fan and condenser coil; a hot, dirty condenser or a stopped fan raises head pressure and current, forcing the compressor to trip its overload.
• Verify outlet voltage at 120V +/- 5 percent under load; low or sagging voltage causes hard starts and repeated overload trips even on a healthy compressor.
• Touch the compressor dome (carefully, power removed) for excess heat, which indicates repeated locked-rotor attempts cooking the windings.

Isolation tree

Use the sound to pick the branch, then confirm electrically.

1. Click (overload trip) branch: A periodic click-hum-pause means the overload is protecting the compressor from locked-rotor current. The cause is usually a failed start relay (compressor cannot phase in the start winding) or a high-head-pressure condition (dirty condenser, dead condenser fan). Test and replace the relay/overload first; clean the condenser and verify the condenser fan. If the compressor still trips with a good relay and clean condenser, it is electrically or mechanically stalling.
2. Hum (stall) branch: A steady hum with no start points at a compressor that energizes but will not turn, or a start device not engaging the start winding. Ohm the windings: run (R-C) and start (S-C) each a few ohms, infinite to the case. Good windings plus a steady hum and no start after a relay swap point at a mechanically locked compressor.
3. Buzz (relay/mechanical) branch: A buzz with cooling loss usually traces to a chattering relay or an inverter board on variable-speed units failing to drive the compressor. A buzz without cooling loss is often a fan blade hitting frost or a vibrating tube and is not a start-circuit fault.

Confirming diagnosis

The overload/relay branch is confirmed when a fresh relay and a clean condenser with a working fan stop the click-hum-trip cycle and the compressor runs and cools. The compressor is confirmed as failed when, with a good relay and clean condenser, it still hums and trips or shows windings out of spec or grounded to the case. The relay/mechanical buzz branch is confirmed by visible relay chatter, an inverter fault, or a mechanical strike found on inspection. The key separating test: swap the relay and clean the condenser first; persistent trips or hum with good windings condemn the compressor.

Remediation

• Click/overload: Replace the start relay and overload as a set, clean the condenser coil, and confirm the condenser fan runs. Recheck start behavior and run current.
• Hum/stall: Replace a compressor with out-of-spec or grounded windings, or a confirmed mechanical lock, after ruling out the relay. Sealed-system work requires EPA 608.
• Buzz/mechanical: Replace a chattering relay or failed inverter board; correct any fan-strike or tubing-vibration cause.

Confirm normal run current and a full pulldown after repair.

References

• EPA, 40 CFR Part 82, Subpart F (Section 608 certification and refrigerant recovery)
• UL 250, Standard for Household Refrigerators and Freezers
• DOE, 10 CFR Part 430, Subpart B (energy conservation standards, refrigerators and freezers)
• NFPA 70 (NEC), appliance branch-circuit supply requirements