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PT Chart — Glide refrigerants (R-407C / R-410A / R-454B) dew/bubble temperature difference in detail

Likely causes

Dew Point vs Bubble Point — which one to use?

Check: PT charts list two temperatures per pressure. Low side (suction, evaporator outlet, fully vaporized): use Dew temperature. High side (discharge, condenser inlet, beginning to liquefy): use Bubble temperature. Pure refrigerants (R-22, R-134a) have identical dew and bubble.

What to do: Superheat = measured suction line temperature − Dew temperature at low side gauge pressure. Subcooling = Bubble temperature at high side gauge pressure − measured liquid line temperature. R-407C glide ≈ 5–7°C, R-454B ≈ 1.5°C, R-410A < 0.1°C (treated as near-azeotrope).

Glide refrigerant leak — why partial recharge (top-off) is forbidden

Check: R-407C, R-410A, R-454B are zeotropic blends. On leak, the lower-boiling component escapes first, shifting remaining composition. Topping off with fresh blend (original ratio) compounds the imbalance — pressures, superheat, subcooling all diverge from PT chart.

What to do: Procedure for glide refrigerant leak: ① stop leak → ② fully recover remaining charge → ③ evacuate to ≤500 microns → ④ recharge as liquid (never as vapor — vapor charging shifts composition again). Maintain liquid phase from recovery to recharge. R-410A glide is tiny so vapor charge is acceptable but liquid still preferred.

Field tip

Glide refrigerant diagnostic pitfall: many old gauges print color-band scales (blue=low, red=high) using R-22 dew/bubble averages. Use a digital manifold or R-407C-specific gauge. Reading R-407C on legacy gauges introduces ±2–3°C error.

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