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Abnormal subcooling from condenser fouling/tube blockage — trim diagnosis

Likely causes

Air-cooled condenser fin fouling — insufficient subcooling + high discharge pressure

Check: Measure: ① liquid line temperature (condenser → TXV line) with clamp probe. ② High-side gauge pressure → bubble temperature from PT chart = condensing saturation temp. ③ Subcooling = ② − ①. Normal 8–12°C. ④ Measure ambient at condenser inlet → condensing temp − ambient = TD. Normal 12–17°C. Fin fouling: TD rises (>20°C) + discharge pressure rises + subcooling lower than normal (poor air-side cooling, so condenser outlet is not cooled enough).

What to do: Procedure: ① Shut down condenser, clean fin exterior (coil cleaner + low-pressure rinse, spray along fin direction). ② For heavy mold/grease, foam-clean with alkaline coil cleaner and rinse. ③ If fins are bent, straighten with fin comb. ④ One hour after restart, compare readings: TD restored to 12–17°C, subcooling 8–12°C, discharge pressure normal = complete. ⑤ Recommended cleaning interval: urban general 6 months, industrial/coastal 3 months, near kitchens (grease) 1–2 months.

Water-cooled condenser tube scale/slime — insufficient subcooling + rising condensing pressure

Check: Measure: ① cooling water inlet and outlet temperature → outlet−inlet = ΔT_w. Normal 5–10°C (verify design). ② PT-derived condensing temperature − average water temperature = approximate LMTD. Normal 5–8°C. ③ As slime/scale builds: ΔT_w drops (heat transfer down, water heats less) + condensing temp ↑ + LMTD ↑ + subcooling ↓. ④ Verify cooling water flow is normal (check strainer, pump). Low flow gives a different diagnosis.

What to do: Procedure: ① Chemical tube cleaning — isolate condenser, circulate weak acid descaler (phosphoric or citric base, 5–10%, with corrosion inhibitor) for 1–3 hours. ② Mechanical cleaning — isolate, pass brush rods through tubes. Effective when slime dominates. ③ Thorough rinse + corrosion-inhibitor passivation. ④ One hour after restart, recompare ΔT_w, LMTD, subcooling. ⑤ Routine: monitor water quality (hardness, pH, microbiology), condenser ΔP (clean when ΔP rises >30%). Suggested interval: general 6 months, river/well water 3 months.

Field tip

Condenser trim diagnostics rule: subcooling alone is rarely conclusive — always read four signals together (subcooling, TD/LMTD, discharge pressure, ambient or water ΔT). Together they distinguish fouling vs. low charge vs. low fan/water vs. non-condensables. Single-signal diagnoses miss often.

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