Vacuum Drying (Evacuation) (Refrigerant Circuit) - Mitsubishi Electric CMB-WP108NU-AA Service Handbook

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[8] Vacuum Drying (Evacuation) (Refrigerant Circuit)

(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 0.5 Torr (65 Pa) or lower degree of vacuum after 5 minutes of operation, and connect it di-
rectly 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 5 Torr (650 Pa) and measures at intervals of 1 Torr (130 Pa).
(A recommended vacuum gauge is shown in Photo2.)
Do not use a commonly used gauge manifold because it cannot register a vacuum degree of 5 Torr (650 Pa).
4. Evacuation time
After the degree of vacuum has reached 5 Torr (650 Pa), 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 1 Torr (130 Pa) 1hour after evacuation. A rise by less than
1 Torr (130 Pa) is acceptable.
If the vacuum is lost by more than 1 Torr (130 Pa), 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.
HWE2206A
-20°C (-4°F) -15°C (5°F)
0.77 Torr (103 Pa) 1.24 Torr (165 Pa)
Recommended vacuum gauge:
ROBINAIR 14010 Thermistor Vacuum Gauge
-10°C (14°F)
1.95 Torr (260 Pa) 3.01 Torr (402 Pa)
- 9 -
(Photo2) 14010
-5°C (23°F) 0°C (32°F)
4.58 Torr (611 Pa)
GB