AC New Install — Evacuation and Vacuum Decay Test Procedure

Question

Accepted Answer

Step 1 — Connect vacuum pump and remove valve cores (use CRT). Check: Connect digital micron gauge to system. Prepare 4 CFM+ vacuum pump (6–8 CFM for long lines / multi-zone). Verify fresh pump oil. Use 3/8" hoses or direct connection instead of standard 1/4" to reduce restriction. What to do: Use CRT (Core Removal Tool) to remove Schrader valve cores at service ports. With cores in place, evacuation takes 2–3× longer. The CRT's isolation valve lets you isolate the pump/hoses for decay testing — essential for accurate Decay measurement. Step 2 — Evacuation (target ≤500 microns, Korean std −100.7 kPa). Check: Run vacuum pump. Monitor with micron gauge in real-time — analog manifold gauges cannot read 500 μm; never rely on them. Short lines (under 5 m) = 15–30 min; long lines / multi-zone = 2.5+ hours. Below 5°C ambient, water can freeze in the system — use triple evacuation. What to do: After reaching ≤500 μm, run pump additional 5–10 min — fully purge moisture from deep system points. For new installs, target ≤300 μm. If moisture detected (rapid pressure rise in decay test), apply triple evacuation: 1000 μm → 5 psig N₂ for 5 min → 500 μm → 5 psig N₂ for 5 min → 200–300 μm. Step 3 — Vacuum Decay Test: hold within 100 μm rise after 10-min isolation. Check: After reaching target vacuum (300–500 μm), close CRT isolation valve. Stop vacuum pump — isolate gauge to read only system pressure. Monitor micron gauge for 10 min. Korean standard is more lenient: 1 hour holding −100.7 kPa (5 torr ≈ 5000 μm) after pump-off; for new installs the 10-min ≤100 μm rule is recommended. What to do: Interpret pressure rise pattern: (1) Stable within 100 μm = pass, proceed to charging. (2) Quick rise then stable (e.g., 500→2000 μm settling) = residual moisture, additional or triple evacuation. (3) Continuous rise (e.g., 500→5000→10000+) = leak — trace with nitrogen pressure test, then repair. ASME B31.5 limit: design pressure ±10%.

AC New Install — Evacuation and Vacuum Decay Test Procedure

Likely causes

Step 1 — Connect vacuum pump and remove valve cores (use CRT)

Step 2 — Evacuation (target ≤500 microns, Korean std −100.7 kPa)

Step 3 — Vacuum Decay Test: hold within 100 μm rise after 10-min isolation

Related cases