AC Compressor Lockout — Inverter Won't Start (LG CH21 / Samsung E311)

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Accepted Answer

Field Step 1 — Narrow down from user-reported symptoms. Check: Branch by user-reported symptom: ① 'humming/buzzing' + no cooling = compressor trying to start but locked. ② Outdoor silent + no sound = power/PCB/comm cable. ③ Breaker tripped = suspect zero compressor insulation. ④ Bill doubled + weak cooling = compressor partially running (overload). Ask user: 'What sound from outdoor?' / 'Did breaker trip?' What to do: Pre-visit guidance to user: ① Switch breaker OFF (NEVER reset — fire risk). ② Remove obstacles around outdoor. ③ Have model/year ready. On arrival: bring megger, clamp meter, manifold, LG/Samsung error-code manual in service bag. Field Step 2 — Confirm cause via insulation, current, error code. Check: 1) Megger (500V DC) on U-V, V-W, W-U, ground. **<1 MΩ = compressor insulation broken → replace compressor**. 2) PCB code: LG CH21 (IPM Fault/DC Peak) → check IPM module + heatsink. Samsung E311–E320 = 4-way valve / E459 = compressor lock. 3) Run current >1.2× nameplate RLA = overload. 4) Suction normal but discharge won't rise = internal compressor wear (valve leak). What to do: **Insulation = 0 → replace compressor** (KRW 250–800k residential Korea). **IPM short → replace whole PCB** (IPM not sold separately). **4-way valve coil open → replace coil** (replace valve body if body shorted). **Compressor lock with normal insulation** = small AC units have start/run capacitor as essential part → check capacitance (±6%) mandatory; if out of spec, replace with same rating. If lock persists, use hard-start kit or replace compressor. After replace: recover → vacuum → weighed recharge + new filter-drier mandatory.

AC Compressor Lockout — Inverter Won't Start (LG CH21 / Samsung E311)

Likely causes

Field Step 1 — Narrow down from user-reported symptoms

Field Step 2 — Confirm cause via insulation, current, error code

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