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Undersized Suction Line — Excessive Pressure Drop

Likely causes

Suction pipe undersized — piping not replaced after refrigeration capacity increase

Check: Measure pressure difference between compressor suction port and evaporator outlet — over 0.2 bar confirms undersizing; over 0.5 bar means 2–3°C evaporating temperature loss

What to do: Recalculate and replace pipe: e.g. R-22 from 7/8″ (22 mm) to 1-1/8″ (28 mm) if capacity increased 20%+; redo equivalent length calc (1 elbow ≈ 0.6 m equivalent)

Pipe not re-evaluated after refrigerant change — pressure drop changes with density/viscosity

Check: Check refrigerant change history; R-410A allows ~20% smaller diameter than R-22 — if not resized, pressure drop worsens

What to do: Re-apply refrigerant-specific pipe sizing charts and replace if needed; recheck suction line insulation — poor insulation increases superheat → raises specific volume → worsens pressure drop

Field tip

Suction line pressure drop of 0.5 bar equals ~2–3°C evaporating temperature loss = ~5–8% capacity reduction — one pipe size upgrade has significant effect

All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.

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