To make this story short, after all the work of fixing my ac system done, I encountered a problem which was my air cond vent sweating whenever I switched it on. I ask the mechanic who fix my a.c and he said it is normal for myvi to be like that after a.c service and it will stop sweating after few month. I trusted in him and for next several month, it doesn't seem to be normal. The air vent keep sweating and it become more obvious for long night driving.
I call back that mechanics and what he replied "don't switch the a.c temp control to too cold". Really angry with his answer as he eager to fix this problem (that time I feel want to cut off his head). As for alternative, I went for a few car a.c workshop, sadly none of them able to fix this problem. All of them came up with same answer "don't switch the a.c to minimum temperature".
Then I bring up my problem to an automotive forum on internet, there I met few forum members who had same problem as mine. One of the forum members told that the problem is due to poor installation of dash where the blower is not attached properly, the blower is not properly clipped to the dash. This cause the blower to blow cold air at wrong angle and cause it to condense.
As I found the root of the problem, I fix this problem myself. First, the thing I had to do is to remove the head unit where the blower is located underneath the air vent. The steps to remove the head unit as in this video
Once the head unit is removed you will see the blower as in pic below:
The clip that need to be properly attached is located in red circle. The picture above shows the clip in position as it should be.
Once the blower is refit to its original position, assembled back the head unit as shown in the video.
It not pretty hard as It looks to fix this. As for me it only takes less than half an hour to fix. Now my myvi air vent no longer sweating.