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Abnormally high suction pressure — distinguish flooded, overcharge, compressor efficiency loss

Likely causes

Flooded indication — high suction + suction line sweat/ice + superheat ≤2°C

Check: Measure: ① Suction pressure >20% above normal. ② Superheat ≤2°C (near zero). ③ Cold sweat or even ice on suction line, possibly extending onto compressor shell. ④ Discharge line temperature lower than normal (liquid refrigerant absorbing heat in cylinder). ⑤ Sight glass shows full liquid, no bubbles, sometimes partial liquid columns. Danger: see superheat-flooded-emergency case — recommend immediate shutdown.

What to do: Action: 1) Stop immediately (cut power). 2) Wait ≥5 min. 3) Diagnose: ① TXV/EEV overfeeding (bulb misplaced, EEV control error), ② evaporator fan stopped (load drop), ③ overcharge, ④ inverter compressor at very low speed (transient). 4) After fix, restart with thermocouple + manifold to monitor superheat — confirm ≥8°C stable before normal operation. 5) If flooding persisted >30 min, recommend oil acidity test + compressor inspection.

Overcharge or compressor efficiency loss — high suction with non-flooded signature

Check: Measure: ① High suction + high discharge + normal superheat (8–12°C) → suspect overcharge. ② Subcooling much higher than normal (>15°C) — excess liquid in liquid line → overcharge near-confirmed. ③ Suction high but discharge slightly low or normal, with both superheat and subcooling normal → suspect compressor valve leakage (worn reed valves). ④ Compression ratio (HP/LP) lower than normal (often should be ~3.5 but reads ≤2.5) = compressor efficiency loss.

What to do: Action: ① Confirmed overcharge: recover some refrigerant to the design charge → recheck subcooling and superheat. Use nameplate/manual for charge spec. ② Confirmed compressor valve leak: both pressures abnormal + low compression ratio + compressor noisy/vibrating → replace or open up the compressor (only some models permit valve plate service). ③ Inverter system: check operating frequency — at very low frequency this can be normal autonomous behavior.

Field tip

The fork in diagnosing high suction is reading 'superheat + discharge' together. SH ≤2°C = flooded (stop now). SH normal + HP also high + subcooling very high = overcharge. SH normal + HP normal/low + low compression ratio = compressor efficiency loss. Relying on a single reading risks the opposite action (e.g., recovering refrigerant from a flooded system).

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