what's this part called?

Can't find shop manual and need to know name of part. 96 exp v6. As you face the vehicle, it's located in upper l/h quadrant of engine compartment. Black plastic manifold looking thing about the size of your palm, part of cooling system. 2 hoses connected to either side. Vacuum line going to top of enclosed diaphram which operates little metal lever. Coolant leaking where lever enters plastic housing. Any ideas? Thanks in advance.....

possibly could be talking about the heating supply?

Sounds like the heater control valve that allows coolant to pass through the heater core when the vacuum controls in the instrument cluster call for heat.

-Rod