Superheat Too Low (

Question

Superheat Too Low (<3°C) → Liquid Slugging Into Compressor

Accepted Answer

TXV over-feeding — spring setting too low or poor bulb contact. Check: SH = suction line temp (clamp meter) minus low-side saturation temp — <3°C = too low. Check bulb (12 o'clock, insulation intact), try to wiggle bulb by hand (loose band?). Measure compressor discharge line temp — much lower than normal or frost on suction line = liquid flooding in progress What to do: Turn TXV adjustment screw 1/4 turn clockwise (increases SH) → wait 15 min → remeasure. Target 5–8°C. If bulb is loose, re-clamp and reinsulate. If adjustment has no effect, replace TXV assembly. Before adjusting, consider shutting compressor off to prevent damage EEV target SH set too low (≤2°C). Check: Enter EEV controller parameter menu → check SH setpoint. ≤2°C = too low. Parameter codes differ by brand (Dixell, Danfoss, Carel) — consult manual. Large gap between actual SH and setpoint also hints at sensor issues What to do: Change SH setpoint to at least 5°C, recommended 6–8°C. Systems with frequent low-load operation → set 7°C or higher. After change, watch 30 min to verify actual SH tracks setpoint; if deviation large, retune PID (Kp, Ti). Record changes in controller log Refrigerant overcharge → liquid remaining at evaporator outlet. Check: Measure subcooling — liquid line temp − condensing saturation temp. >10°C suspects overcharge. Completely clear liquid sight glass (no bubbles) + high discharge pressure. Ask about recent top-offs What to do: If overcharged, recover excess from high side with recovery machine — liquid recovery is faster. Stop when subcooling is 5–8°C, high pressure normal, light bubbles in sight glass. Record amount recovered; finally verify total charge weight against nameplate Bulb mis-located — right at evaporator outlet, insulation missing. Check: Check bulb location and insulation — correct placement is 10–20 cm downstream of evaporator on top (12 o'clock) of horizontal suction line. Right at outlet reads liquid refrigerant temp incorrectly; no insulation = influenced by ambient air What to do: Relocate bulb 10–20 cm downstream of evaporator on top (12 o'clock) of horizontal suction line → clamp tight with stainless band → 2 wraps of rubber insulation, 3 cm overhang each end → finish with aluminum tape. After, verify SH 5–8°C, watch 30 min to stabilize Sudden load drop (unloaded at night) → TXV response lag. Check: Observe frost on suction line during low-load/overnight hours; log SH over time with datalogger. If SH drops to 0–2°C briefly after load changes, response lag confirmed. Common in cold storage/buffer tank systems with intermittent operation What to do: Short-term: enable capacity control (unloader/VFD) at low load to eliminate extreme low-load points. Medium-term: upgrade TXV to EEV — far better response. Raise SH setpoint to 7°C+. If low-load operation is frequent, consider multi-stage compressor system

Superheat Too Low (<3°C) → Liquid Slugging Into Compressor

Likely causes

TXV over-feeding — spring setting too low or poor bulb contact

EEV target SH set too low (≤2°C)

Refrigerant overcharge → liquid remaining at evaporator outlet

Bulb mis-located — right at evaporator outlet, insulation missing

Sudden load drop (unloaded at night) → TXV response lag

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