LG Multi F A2UW14GFA0 Engineering Product Data Book page 324

2. Guideline for each installation process
2.7. Vacuum drying work
2.7.1 What is Vacuum drying?
Vacuum drying is : The use of a vacuum pump to vaporize(gasify) the moisture (liquid) inside the pipe and expel it leaving
the pipes completely dry inside.
At 1 atm(760mmHg) the boiling point (evaporating temperature) of water is 100°C but if a vacuum is
created inside the pipes using a vacuum pump then the boiling point is rapidly reduced as the degree of
the vacuum is increased.
If the boiling point is reduced to a level below that of the ambient temperature then the moisture in the
pipes will evaporate.
Example
When outside temperature is 11.7°C as shown in the table on the right
, the degree of vacuum must be lowered below -750mmHg
The evacuation of air conditioner piping provides the following effects.
- Vaccum drying
- Removes air and nitrogen(used in air-tightness test) from the inside
of pipes.
Therefore , it is necessary to ensure that both purposes have been
achieved in the vacuum drying operation.
NOTE
Key point: Maintain a vacuum level of -755mmHg
29 _
Heat pump 50Hz/R410A
Boilng point of
water(°C)
40
30
26.7
24.4
22.2
20.6
17.8
15.0
11.7
7.2
0
0
60
160
260
360
460
560
660
670
680
690
700
710
720
730 730 730
3.8MPa
740
Required degree
755
of vaccum
Evaporation
point
mmHg
760
-20 -10 0 10
Temperature
The degree
Pressure
of a vacuum
mmHg Pa Torr
-705 7,333 55
-724 4,800 36
-735 3,333 25
-738 3,066 22
-740 2,666 20
-742 2,400 18
-745 2,000 15
-747 1,733 13
-750 1,333 10
-752 1,066
-755 667
760mmHg
700
600
500
400
300
200
100
90
70
60
50
40
30
20
10
5
Outside
temperature
range
0 mmHg
20 30 40 50 60 70 x
(C)
8
5