System Evacuation Procedure — Quick Reference

Preliminary Safety and Setup

• Recover refrigerant; bleed nitrogen after pressure test; ensure system is at $0\ \text{PSIG}$.

Initial Gauge-Set Vacuum Test

• Verifies: hoses leak-free, micron gauge works, pump can pull to $500\ \text{microns}$.
• If micron gauge thermistor is oil-contaminated, flush with isopropyl alcohol.
• Ensure vacuum pump oil is clean and dry; dirty/moist oil reduces achievable vacuum.

Evacuation Procedure (Gauge-Only First)

• With gauge and service valves closed, start pump; pull center charging hose to $500\ \text{microns}$.
• Open manifold gauges; pull hoses to $500\ \text{microns}$.
• If moisture or residual refrigerant present, purge and proceed.

Full System Evacuation

• With pump running, open suction service valve and discharge line service valve; evacuate until the entire system reaches $500\ \text{microns}$.
• If a liquid receiver and separate micron gauge are used, compare readings for consistency.

Hold Vacuum and Moisture Check

• Close pump valve; hold vacuum for $5\ \text{minutes}$ to verify leaks and moisture absence.
• Expect a rise in the micron level after valve-off; if it climbs to between $1500\ \text{microns}$ and $50000\ \text{microns}$ and stays, moisture is boiling off; continue vacuum.
• Continue vacuuming until you can hold below $1000\ \text{microns}$ for $5\ \text{minutes}$.

Readiness to Charge

• If vacuum holds below $1000\ \text{microns}$ for $5\ \text{minutes}$, system is ready to charge.

Time Considerations and Common Pitfalls

• Not a quick 5–10 minute procedure; moisture increases duration.
• The longer the system is open to the atmosphere, the more moisture is present and the longer the evacuation.

Quick Recap of Steps

• Recover refrigerant, bleed nitrogen, ensure $0\ \text{PSIG}$.
• Verify gauge-set vacuum to $500\ \text{microns}$.
• Check and, if needed, clean oil; flush oil if thermistor is oil-contaminated.
• Evacuate gauge-only to $500\ \text{microns}$; then evacuate entire system to $500\ \text{microns}$.
• Hold vacuum for $5\ \text{minutes}$; if moisture is present, continue evacuation until hold is under $1000\ \text{microns}$ for $5\ \text{minutes}$.
• Proceed to charging once criteria are met.

Note on Time Variability

• A completely moisture-free system can reach the target quickly, but moisture presence will extend the duration significantly.