AC New Install — Nitrogen Pressure Leak Test (Low/High Side)

Question

Accepted Answer

Step 1 — Safe nitrogen (N₂) pressurization (never use air or oxygen). Check: OFN (Oxygen-Free Nitrogen) cylinder + 2-stage pressure regulator required. Compressed air introduces moisture/oil; oxygen oxidizes compressor oil and risks ignition. Standard system pressure: R-410A low 150 psig / high 450 psig, R-22 low 150 / high 300 psig, R-32 300–550 psig. Before use, verify primary safety valve and regulator gauge function. What to do: Connect charging hose to service port → close both manifold valves → open cylinder main valve → slowly raise to target pressure via regulator (~50 psi/min). After reaching target, close cylinder main valve. Never pressurize one side only — always pressurize low and high sides simultaneously (protects compressor and check valve). Step 2 — Holding time and leak tracing (soap bubble / electronic detector). Check: Residential (home AC): hold 30–60 min. Commercial (VRF/large): hold 24–48 hr. ASME B31.5 minimum: design pressure +10% for 15 min. Acceptable pressure drop: zero on precise gauge (1 psi drop = suspect leak). Correct for ambient temperature — ~0.3% pressure change per 1°C. What to do: If pressure drops, trace leak: ① Apply micro-foam (specialized leak solution) to suspect area → observe 10–15 min (small leaks form bubbles slowly) — more reliable than household soap. ② Electronic leak detector (A2L-compatible for R-32) — adding 5% tracer gas improves accuracy. After locating leak, fully release N₂ → re-work joint → re-test.

AC New Install — Nitrogen Pressure Leak Test (Low/High Side)

Likely causes

Step 1 — Safe nitrogen (N₂) pressurization (never use air or oxygen)

Step 2 — Holding time and leak tracing (soap bubble / electronic detector)

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