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11. Vacuum Drying and Leakage Checking
OUTDOOR UNIT
mrcool.com | Page 15
Purpose of vacuum drying
• Eliminating moisture in system to prevent the phenomena of ice-blockage and copper oxidation
Ice-blockage can cause abnormal operation of system, while copper oxide can damage the
compressor.
• Eliminating the non-condensable gas (air) in the system to prevent the components from oxidizing,
pressure fluctuation, or bad heat exchange during the operation of system.
Selection of vacuum pump
•The vacuuming capability of the vacuum pump should be 756 mmHg or above.
•Precision of vacuum pump should reach 0.02 mmHg or above.
Operation procedure for vacuum drying
There are two kinds of vacuum drying that can be used depending on the environment, when the unit
is installed. These are ordinary vacuum drying and special vacuum drying. These consist of the
following:
Ordinary vacuum drying
1. When conducting the first vacuum drying, connect pressure gauge to the infusing mouth of the gas
pipe and liquid pipe, and keep vacuum pump running for an hour (vacuum degree of vacuum pump
shall be reached -755mmHg).
2. If the vacuum degree of vacuum pump can not reach -755 mmHg after 1 hour of drying, it indicates
that there is moisture or leakage in the pipeline system and will need to continue drying for half an
hour.
3. If the vacuum degree of vacuum pump still can not reach -755 mmHg after 1.5 hours of drying,
check for leaks.
4. Leakage test : After the vacuum degree reaches- 755 mmHg, stop vacuum drying and keep the
pressure for 1 hour. If the indicator of the vacuum gauge increases, that indicates that there is still
moisture or a leak present.
Special vacuum drying
The special vacuum drying method should be used when:
1. Finding moisture during flushing the refrigerant pipe.
2. Conducting installation on a rainy day, because rain water could penetrate into the pipeline.
3. Install period takes an extended amount of time, rain water might penetrate into the pipeline.
4. Be sure to use a micron gauge during vacuuming that can hold under 800 microns. Pull down to
500 microns.