Refrigerator Compressor Clicks and Trips Overload
A domestic refrigerator with a hermetic compressor, a PTC starter and an overload protector is reported warm in both compartments. The compressor attempts to start, clicks, hums for about 5 s and then the overload trips; it retries after cooling. Supply voltage at the socket is 230 V and remains stable during the attempt. Nameplate values are RLA 1.1 A and LRA 6.5 A. A clamp meter shows 11 A during the start attempt. Winding resistances measured at the compressor terminals are: common-to-run 12 Ω, common-to-start 28 Ω, run-to-start 40 Ω. Insulation resistance to the metal shell is 60 MΩ at 500 V. The PTC starter reads about 15 Ω cold but rattles when shaken. The technician proposes replacing only the PTC starter and restarting the unit immediately.
1. Use the winding resistance readings to decide whether the compressor motor windings are electrically sound. Show the expected relationship.
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For a split-phase/CSR compressor, the run and start windings are connected at the common terminal, so the resistance measured between run and start should equal the sum of the two winding resistances: 12 Ω + 28 Ω = 40 Ω, which matches the measured run-to-start value. The start winding has the higher resistance, as expected. The insulation resistance of 60 MΩ at 500 V is also high, indicating no serious winding-to-shell leakage. Therefore the motor windings are electrically continuous and balanced; the readings do not support a open or shorted winding. The fault is more likely in the starting circuit or the mechanical compressor. However, resistance tests do not prove that the compressor is not mechanically seized.
2. Interpret the 11 A start current against the nameplate LRA and explain why replacing only the PTC may not solve the fault.
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The nameplate locked-rotor current is 6.5 A, but the measured start current is 11 A, about 70% above LRA. That indicates a locked rotor, a mechanical seizure, a shorted turn, or a start winding/run capacitor fault-not merely a worn PTC. The PTC may be damaged because it has been carrying this excessive current, so replacing it could restore starting for a short time but the underlying high current will destroy the new part or trip the overload again. The rattling PTC is suspect and should be replaced as a set with the overload protector, but only after confirming that the compressor current is normal with known-good starting components. Do not bypass the overload to force a start.
3. Outline a safe diagnostic sequence before condemning the compressor.
Read the worked answer
Isolate the refrigerator, lock off the plug, and discharge any run capacitor. Inspect the PTC, overload and terminals for burning; check the run capacitor if fitted. Measure winding resistances and insulation resistance as already done. Verify supply voltage and wiring. Then reconnect known-good start components and apply power briefly while watching a clamp meter; do not leave the unit unattended or repeatedly reset the overload. If the current remains near 11 A and the compressor hums without starting, the compressor is mechanically seized or internally damaged and requires replacement. If current falls within LRA and the unit runs, replace the faulty start components and check the cooling performance.