Mitsubishi Electric BDT CITY MULTI Installation And Pre-Commissioning Booklet page 6

• A two-stage vacuum pump with fresh vacuum pump oil capable of a vacuum of 50 microns should be selected. Where
possible it is best engineering practice to have a pump specifically for installations rather than the service pumps which tend
to deteriorate during service tasks.
• Using a 3/8" connection line to the manifold is important to allow quicker vapour volume removal.
• An accurate vacuum gauge is an essential tool to gauge the system tightness and the effectiveness of the evacuation
procedure. A vacuum of 1000 microns should be reached on the initial vacuum test. A rapid rise indicates a leak is present.
A small, slow rise indicates the possible presence of moisture. The slow rise is due to the moisture molecules slowly
detaching from the pipe surface and starting to expand in the vacuum void. This is why the vacuum must be held for a time.
Installation time and commissioning schedules often affect the time available for the ideal vacuum procedure.
It cannot be reinforced enough that an effective vacuum process is critical to the system's long term operation and
warranty compliance.
• When possible it is preferable to use copper lines for evacuation purposes, as gauge hoses are porous when trying to
measure accurate deep vacuum.
06. RECOMMENDED TRIPLE EVACUATION PROCEDURE
1. Connect the vacuum pump, check valve, vacuum gauge, charge line with the access cores removed and pull an initial
vacuum of 1000 microns. Hold vacuum for 1 to 2 hours and monitor.
2. Break vacuum with dry nitrogen to 1 to 2 bars and release nitrogen.
3. Evacuate to 500 microns or less. Hold and monitor for 1 to 2 hours.
4. Break vacuum with dry nitrogen to 1 to 2 bars and release nitrogen.
5. Refit access valve cores. Evacuate down to best vacuum as close to 200 microns as possible. Hold for 8 hours.
6. Add additional refrigerant while system is under vacuum (as calculated from pipe lengths). Open outdoor unit isolation
valves. System should now be ready for commissioning.
VACUUM MEASUREMENT COMPARISONS
1 TORR =
1 TORR 1000 =
microns 1000 =
microns =
NOTE: BDT reserves the right to cut sections of pipe open and inspect if there
is any doubt dry nitrogen has not been purged through the pipe work during the
welding of any copper connections.
6
1mm HG
1000 microns
29.88" HG (inches or mercury)
1mm HG