Refrigerant Undercharge — Symptoms, Diagnosis, Leak Check

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Primary symptoms — both high and low pressures low + sight glass bubbles + very high superheat. Check: Standard diagnosis: high-side >0.3 MPa below normal + superheat >20°C + subcooling 0–3°C → confirmed undercharge. Partial frosting on suction line and asymmetric icing on one side of evaporator are also signs. What to do: 1) Leak check first — never just top off. 2) After locating leak: recover → repair → evacuate 30 min → recharge by weight. 3) Emergency top-up only with leak repair scheduled within 1 week. 4) Never 'just top off and call it done' — violates environmental law and creates repeat work. Leak detection tools and techniques — efficiency-ranked order. Check: 1) Visual inspection — oil traces, corrosion marks. 2) Soap solution — reliable for larger leaks. 3) Electronic detector — halide/infrared/ultrasonic types. 4) Fluorescent dye + UV light — useful for micro leaks. 5) Nitrogen pressurization (with system empty) — combine all methods. What to do: 1) First catch large leaks with visual + soap. 2) If not found, use electronic detector for fine inspection (sensitivity ≤5 g/year recommended). 3) Still not found → inject fluorescent dye + return after few days with UV light. 4) Photograph leak location — permanent record in service report and history. Common leak locations — priority inspection order. Check: 1) Flare nuts (most common) — loosen due to vibration/temp cycling. 2) Brazed joints — bad braze or corrosion. 3) Condenser coil — corrosion/damage (especially coastal). 4) Evaporator coil — vinegar/food chemical corrosion. 5) Service valve cores — smallest but frequent leak source. What to do: 1) Flare nuts — re-torque with torque wrench (¼" 14 N·m, ⅜" 35 N·m, 5/8" 65 N·m). 2) Brazed joints — re-braze with copper/brass. 3) Coil damage — decide partial repair vs full replacement. 4) Service valve cores — replace core, tighten cap firmly. 5) For widespread corrosion, also recommend environmental control (salt, chemicals).

Refrigerant Undercharge — Symptoms, Diagnosis, Leak Check

Likely causes

Primary symptoms — both high and low pressures low + sight glass bubbles + very high superheat

Leak detection tools and techniques — efficiency-ranked order

Common leak locations — priority inspection order

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