Micron-gauge vacuum evacuation & decay test procedure (HVAC Laboratory)

Source: HVAC Laboratory (practitioner HVAC guide). Credibility: Medium (authoritative trade technique; not peer-reviewed).

Key points

• Target: pull to 500 µm (~0.067 kPa) or lower; evacuate deep first, then admit refrigerant.
• Pump: two-stage rotary-vane mandatory (single-stage can’t beat 1000 µm), 4–8 CFM; healthy system <2000 µm in 2–3 min.
• Decay test: isolate, watch 10 min — pass <200 µm rise, fail >500 µm; gauge mounted at the vessel.
• Non-condensables: nitrogen sweep 2–3× before evacuation; pump boils off residual moisture over 30–60 min.