Midea Forest MOAA31-12CN1-NB8, Technical Manual

 Installation

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 Page 47 

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6.  Vacuum Drying and Leakage 

Checking

6.1  Purpose of vacuum drying

•

Eliminating moisture in system to prevent the phe-
nomena of ice-blockage and copper oxidation

.

          Ice-blockage shall cause abnormal operation of  
           system, while copper oxide shall damage 

           compressor. 

•

Eliminating the non-condensable gas (air) in system 
to prevent the components oxidizing, pressure fluc-
tuation and bad heat exchange during the operation 
of system. 

6.2  Selection of vacuum pump

•

The ultimate vacuum degree of vacuum pump shall 
be -756mmHg or above. 

•

Precision of vacuum pump shall reach 0.02mmHg or 
above. 

6.3  Operation procedure for vacuum 

drying

Due to different construction environment, two kinds of 
vacuum drying ways could be chosen, namely ordinary 
vacuum drying and special vacuum drying.

6.3.1  Ordinary vacuum drying

1.

When conduct first vacuum drying, connect pressure 

gauge to the infusing mouth of gas pipe and liquid pipe, 
and keep vacuum pump running for 1hour (vacuum 
degree of vacuum pump shall be reached -755mmHg).

2. If the vacuum degree of vacuum pump could not reach 
-755mmHg after 1 hour of drying, it indicates that there is 
moisture or leakage in pipeline system and need to go on 
with drying for half an hour. 

3. If the vacuum degree of vacuum pump still could not 
reach -755mmHg after 1.5 hours of drying, check whether 
there is leakage source. 

4 . Leakage test: After the vacuum degree reaches 
-755mmHg, stop vacuum drying and keep the pressure for 
1 hour. If the indicator of vacuum gauge does not go up, 
it is qualified. If going up, it indicates that there is moisture 
or leak source. 

6.3.2  Special vacuum drying

The special vacuum drying method shall be adopted when: 

1. Finding moisture during flushing refrigerant pipe. 

2. Conducting construction on rainy day, because rain 

water might penetrated into pipeline. 

3. Construction period is long, and rain water might 
penetrated into pipeline.

4. Rain water might penetrate into pipeline during 
construction.

Procedures of special vacuum drying are as follows: 

1. Vacuum drying for 1 hour.

2. Vacuum damage, filling nitrogen to reach 0.5Kgf/cm2 . 

Because nitrogen is dry gas, vacuum damage could 
achieve the effect of vacuum drying, but this method 
could not achieve drying thoroughly when there is too 
much moisture. Therefore, special attention shall be drawn 
to prevent the entering of water and the formation of 
condensate water.

3. Vacuum drying again for half an hour.

If the pressure reached -755mmHg, start to pressure 
leakage test. If it cannot reached the value, repeat vacuum 
damage and vacuum drying again for 1 hour.

4. Leakage test: After the vacuum degree reaches 
-755mmHg, stop vacuum drying and keep the pressure for 
1 hour. If the indicator of vacuum gauge does not go up, 
it is qualified. If going up, it indicates that there is moisture 
or leak source.