I have a broken white tube of some sort and I don't know what it is. Can anybody help tell me what this is for?

 

Looks like the tube that activates the doors on the heating system. Easy fix cut both ends of the break with a razor blade or sharp knife. you can then use a pc of vacume line to join the 2 pc back togeather. or you can use a pc of shrink tube but you sorta need 4 hands to do that someone to hold things tight togeater while the other person shrinks the tube. those are a comon break as they get pretty brittle over time...

 

Thax, I will use some vacuum tube to fix