Mitsubishi Electric PU(H)Y-P250YGM-A, Service Handbook

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Read Before Servicing ]
[8] Vacuum Drying (Evacuation)
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 (Photos 2)
Use a vacuum pump that attains 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 650Pa and measures at intervals of 130Pa. (A recommended vac-
uum gauge is shown in Photo2.)
Do not use a commonly used gauge manifold because it cannot register a vacuum degree of 650Pa.
4. Evacuation time
ΠAfter the degree of vacuum has reached 650Pa, evacuate for an additional 1 hour. (A thorough vacuum drying removes
moisture in the pipes.)
ΠVerify that the vacuum degree has not risen by more than 130Pa 1hour after evacuation. A rise by less than 130Pa is ac-
ceptable.
ΠIf the vacuum is lost by more than 130Pa, conduct evacuation, following the instructions in section 6. Special vacuum dry-
ing.
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.
6. Special vacuum drying
ΠWhen 650Pa or lower degree of vacuum cannot be attained after 3 hours of evacuation, it is likely that water has penetrated
the system or that there is a leak.
ΠIf water infiltrates the system, break the vacuum with nitrogen. Pressurize the system with nitrogen gas to
0.05MPa and evacuate again. Repeat this cycle of pressurizing and evacuation either until the degree of vacuum below
650Pa is attained or until the pressure stops rising.
ΠOnly use nitrogen gas for vacuum breaking. (The use of oxygen may result in an explosion.)
(Photo1) 15010H (Photo2) 14010
Recommended vacuum gauge:
ROBINAIR 14010 Thermistor Vacuum Gauge