Confirming Overcharge with Subcooling — Most Reliable Diagnostic

Question

Accepted Answer

TXV systems — subcooling exceeds normal by 5°C+ = almost certain overcharge. Check: TXV systems normally show subcooling 5–10°C. Measured ≥15°C means liquid refrigerant filling part of condenser, reducing heat exchange area → overcharge signal. High-side simultaneously >0.3 MPa above normal. Superheat normal or slightly low. What to do: 1) Recover via charge-over procedure — 200g increments, wait 5 min between to measure. 2) Target: subcooling 5–10°C + normalized high-side. 3) If subcooling near target but pressure still abnormal, suspect additional cause (e.g., condenser blockage). 4) Document both charge and recovery operations in service report. Capillary systems — subcooling not a valid diagnostic indicator. Check: Capillary systems (small refrigerators, some room ACs) always have varying liquid refrigerant in condenser depending on load — subcooling varies widely with load and ambient. Subcooling cannot diagnose overcharge/undercharge. Use suction line frosting pattern, operating pressures, and current draw instead. What to do: 1) For capillary systems, charge by weight per nameplate spec (use scale). 2) Check that suction line frosting reaches the position marked on nameplate. 3) Measure run current — over ±10% rated suggests overcharge, under ±10% suggests undercharge. 4) Capillary blockage unrelated to subcooling — touch liquid line for warm-cold transition point.

Confirming Overcharge with Subcooling — Most Reliable Diagnostic

Likely causes

TXV systems — subcooling exceeds normal by 5°C+ = almost certain overcharge

Capillary systems — subcooling not a valid diagnostic indicator

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