jureivis:
it is not that i am hiding something - just not sure what is it.
Well there is probably no surprise about that. I suspect the only people who know what it is are the original manufacturer and the original person who was supposed to receive it as what I imagine is a replacement module, which isn't you.
While the device is about the size and shape of a shield for an Arduino it clearly isn't one and has nothing to do with Arduino. It appears to be part of the controls for a refrigeration system.
What harm can i make to a device if i connect 2 more sensors just to try
In the highly unlikely event that you can make it work with three DS18B20s, you can very probably make it work with five. You certainly won't do any harm but it seems the speculation in my previous was right - it's something to be hacked for spare parts.