coolant pipe vacuum question

hi all, one a freelander 1.8exi with aircon there is a vacumm fitting on the lower pipe of the 2 that go into the bulkhead from the engine compartment, part plastic part metal with a vacuum assembly and tube coming off it, what is the part called and where can i get a new one as the metal part has cracked and its leaking water through it?many thanks

further to the above, the conection appears to be a retro fit part.But why.it seems the vacuum from the manifold closes the valve on the coolant pipe to prevent water going to the heater matrix. I have disconected the faulty bit and bypassed it and blocked up the vacuum, it seems ok but would like to know why this was done.