equipment service
System Evacuation (Vacuum Pump)
Pull a system down with a vacuum pump, then prove it is dry and tight.
10 steps3 criticalLimit 30 minAlways tested
Steps
- 1Make sure the refrigerant has already been recovered to the required level (Table 1, or the leak and minor-repair allowances in 82.156), and that level verified, before the system is opened; venting is prohibited, so a vacuum pump is not a way to get rid of refrigerant
- 2Check the pump first: clean oil as the pump maker recommends, and confirm with a micron gauge that the pump alone can pull a deep vacuum
- 3Connect the pump through an O-ring sealed manifold and vacuum-rated lines (copper or metal hose, or vacuum hoses) to both the high and low sides
- 4Connect a micron gauge so it reads the system, not just the pump
- 5Critical stepOpen the valves, start the pump, and pull down to the target vacuum from the manufacturer or your procedure (JB Industries starts its isolation test at 300 to 400 microns; sources differ on targets)
- 6Critical stepClose the isolation (blank-off) valve so the pump is cut off from the system, and watch the micron gauge for the hold time your procedure sets
- 7Read the result: low and steady means the system is dry and tight; a slow rise points to moisture; a rapid rise toward atmospheric pressure points to a leak
- 8If the vacuum does not hold, find and fix the leak or keep dehydrating, then pull down and test again
- 9With the isolation valve closed, shut the pump off; do not let the pump's oil be pulled back into the system or gauge
- 10Only after the vacuum holds, protect the micron gauge from pressure, then break the vacuum with the refrigerant to be charged (or dry nitrogen where your procedure calls for it)
What graders are watching for
Tips
- A compound gauge only shows that a vacuum is being produced; a micron gauge is the tool that tells you how deep it is and whether it holds
- Readings after the pressure rise test: under 500 microns means the evacuation is complete, a slow rise toward about 1500 microns means moisture, and a rapid rise to atmosphere means a leak (JB Industries)
- For commercial refrigeration, EPA GreenChill describes a staged evacuation (1000, then 500, then 300 microns): a dry-nitrogen break after the 1000-micron hold, a refrigerant break after the 500-micron hold, and a final 300-micron vacuum that must stand 24 hours; it says vacuum requirements may be set by the customer or code
Common mistakes
- Opening the system before verifying the recovery level.
- Treating the vacuum pump as a replacement for recovery, which can mean venting refrigerant.
- Mixing up units: Table 1 uses inches Hg vacuum for most appliances but 25 mm Hg absolute for low-pressure appliances; micron gauges read absolute pressure.
- Skipping the isolation hold and calling a system dry because the pump ran a while. The rise (or lack of it) after isolation is the evidence.
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Sources and how we check them: How we verify.