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Superheat near 0°C + suction line sweating/icing — Liquid Floodback emergency response

Likely causes

Why this is an emergency — compressor damage mechanism

Check: Superheat ≤2°C + sweat or ice on suction line = liquid refrigerant entering compressor. Compressors are designed for gas compression, not liquid (hydraulic lock). Results: ① cracked/broken valve plate ② bearing oil dilution (liquid dissolves in oil) → lube failure → bearing seizure ③ motor winding insulation breakdown if liquid refrigerant absorbs into windings.

What to do: Recognizing this mechanism is the action trigger — once you see the warning signs (superheat ≤2°C, suction sweat/ice), shut the system down without delay. The 'Why' step concludes with: move immediately to the emergency procedure below.

Emergency response — immediate shutdown + staged recovery

Check: Verify: compressor shell temperature (normal: suction side cool, discharge side warm 60–80°C). Cold sweat/ice on suction side shell = liquid is entering. Sight glass (if present) showing bubbles/foam = strong floodback indicator. After shutoff hold for ≥5 minutes (allows liquid to boil off and oil to recover).

What to do: Steps: ① shut off immediately (cut power). ② Wait 5 minutes. ③ Diagnose cause (usually TXV/EEV overshoot, evaporator fan stopped, overcharge, poor distribution). ④ After fix, restart with thermocouple + manifold on suction side to monitor superheat live. ⑤ Confirm superheat ≥8°C held for 5 minutes before resuming normal operation. If thick ice persists on suction shell, remove accumulator (if present) and drain residual liquid. If floodback persisted >30 min, recommend oil acid test + compressor inspection.

Field tip

Restarting the compressor immediately after shutdown is taboo — risk of instant destruction by liquid compression. The 5-minute rule is minimum; in cold ambient (winter <0°C) 10 minutes is recommended. Systems without an accumulator lack liquid protection and are more vulnerable to floodback — once it occurs, compressor reliability drops noticeably.

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