Vacuum Drying - Mitsubishi Electric PURY-M200YNW-A1 Service Handbook

[1-3 Working with Refrigerant Piping ]
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Vacuum Drying

(Photo1) 15010H
1. Vacuum pump with a reverse-flow check valve (Photo1)
To prevent the vacuum pump oil from flowing into the refrigerant circuit during power OFF or power failure, use a vacuum
pump with a reverse-flow check valve.
A reverse-flow check valve may also be added to the vacuum pump currently in use.
2. Standard of vacuum degree (Photo 2)
Use a vacuum pump that attains 0.5Torr(65Pa) or lower degree of vacuum after 5 minutes of operation, and connect it directly
to the vacuum gauge. Use a pump well-maintained with an appropriate lubricant. A poorly maintained vacuum pump may not
be able to attain the desired degree of vacuum.
3. Required precision of vacuum gauge
Use a vacuum gauge that registers a vacuum degree of 5Torr(650Pa) and measures at intervals of 1Torr(130Pa). (A recom-
mended vacuum gauge is shown in Photo2.)
Do not use a commonly used gauge manifold because it cannot register a vacuum degree of 5Torr(650Pa).
4. Evacuation time
After the degree of vacuum has reached 5Torr(650Pa), evacuate for an additional 1 hour. (A thorough vacuum drying re-
moves moisture in the pipes.) When the outside temperature drops below 1°C (or when the saturation pressure drops below
656 Pa), continue vacuum drying for another 1 hour after the vacuum degree has reached the saturated vapor pressure of
the water (ice) at the outside temperature. When performing vacuum drying at a low outside temperature, use a vacuum gauge
appropriate for the temperature range.
Degree of vacuum (reference)
Outdoor temp.
Degree of vacuum
* Degrees of vacuum shown above are obtained based on the saturated vapor pressure of ice.
* In a system using water heat exchangers, circulate water to prevent the water in the heat exchangers from freezing during vacuum drying.
Verify that the vacuum degree has not risen by more than 1Torr(130Pa) 1hour after evacuation. A rise by less than
1Torr(130Pa) is acceptable.
If the vacuum is lost by more than 1Torr(130Pa), conduct evacuation, following the instructions in section 6. Special vacuum
drying.
5. Procedures for stopping vacuum pump
To prevent the reverse flow of vacuum pump oil, open the relief valve on the vacuum pump side, or draw in air by loosening
the charge hose, and then stop the operation.
The same procedures should be followed when stopping a vacuum pump with a reverse-flow check valve.
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chapter 1
-20°C (-4°F) -15°C (5°F)
0.77 Torr (103 Pa) 1.24 Torr (165 Pa)
(Photo2) 14010
Recommended vacuum gauge:
ROBINAIR 14010 Thermistor Vacuum Gauge
-10°C (14°F) -5°C (23°F)
1.95 Torr (260 Pa) 3.01 Torr (402 Pa)
0°C (32°F)
4.58 Torr (611 Pa)
BS_01_L