Vacuum Drying - Mitsubishi Electric PUHY-P200 Service Handbook

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Vacuum Drying

Recommended vacuum gauge : ROBINAIR 14010 Thermistor Vacuum Gauge
1. Vacuum pump with reverse-flow check valve (Photo 1)
To prevent vacuum pump oil from flowing back into the refrigerant circuit upon turning off the vacuum pump's power
source, use a vacuum pump equipped with a reverse flow check valve.
A check valve may also be added to the vacuum pump currently in use.
2. Standard of vacuum degree (Photos 1 and 2)
Use a vacuum pump that shows a vacuum degree of 65Pa or less after 5 minutes of operation. Use a pump well-
maintained with an appropriate lubricant.
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
vacuum gauge is shown in Photo 2.)
Do not use a vacuum gauge that does not register a vacuum degree of 650Pa.
4. Evacuation time
• After the vacuum gauge has registered the vacuum degree of 650Pa, evacuate for 1 hour. (A thorough vacuum drying
removes moisture in the pipes.)
• Verify that the vacuum degree has not risen by more than 130Pa 1 hour after evacuation. A rise by less than 130Pa is
acceptable.
• If it has exceeded by more than 130Pa, conduct vacuuming following the instructions in the "6. Special vacuum drying"
section.
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
• When 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. When water infiltration is suspected, vacuum with nitrogen gas.
After breaking the vacuum, pressurize the system with nitrogen gas to a degree of 0.05MPa, and conduct an evacuation
again. Repeat it until 650Pa or lower degree of vacuum is attained or the vacuum pressure rise will be lost.
• Only use nitrogen gas for vacuum breaking. (Use of oxygen may cause an explosion.)
Photo 1 15010H Photo 2 14010
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