R-Pro › Field cases › Air conditioning
AC New Install — Refrigerant Charging by Weight (R-32/R-410A)
Likely causes
Step 1 — Verify nameplate charge and adjust for line length
Check: Read standard charge (g or oz) on outdoor unit nameplate or manual. Factory-charged for default line length (usually 7.5 m). Add proportionally for extra length (R-32 typically 20 g/m, R-410A typically 30 g/m, manufacturer manual prevails). Account for differences by liquid-line diameter.
What to do: Place cylinder on precision scale (0.1 g resolution, A2L-rated). With system OFF, charge as liquid through the high-side service port (R-32 and R-410A both must be charged as liquid). Invert cylinder or use liquid dip tube. Stop immediately at exact nameplate weight.
Step 2 — Verify charge via superheat / subcooling measurement after startup
Check: Stabilize 15–20 min after startup. R-410A target: subcooling 8–12°F (4.4–6.7°C), superheat 10–15°F (5.5–8.3°C). R-32 target: subcooling 10–15°F (5.5–8.3°C). At 70–75°F ambient: suction 118–135 psi, discharge 370–420 psi (R-410A). TXV system → subcooling priority; fixed-orifice → superheat priority.
What to do: High superheat / low subcooling = undercharged → add small amount (re-measure every 5 min). Low superheat / high subcooling = overcharged → recover with recovery unit. R-32 (A2L) mildly flammable — mandatory ventilation, anti-static, no ignition sources. Final leak check at cylinder and service port after charging.
Weight is the most accurate charging basis. Pressure-only (P-T chart) charging is very sensitive to ambient — not precise. Record all 3 datasets (digital scale weight + vacuum + superheat/subcooling) and hand to customer (prevents disputes).
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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