Rubber ball

[ljoaquinl]

Hi guys! I was fixing the aircon of my MK2 and found out that the vaccum is not good. I traced the hose and found a somewhat rubber ball at the end of the hose. I then cut the line and used the other line instead (for it has 2 lines for the vaccum) however, I havent removed the "rubber ball". My AC is now working fine and I am just wondering what is that thing that I found and whats its purpose in the vaccum? Any idea about this?

Thanks!