Originally Posted by
Bzak1pgh
Anyone know what part this is and what it's called so I can order it?
it's coming off the radiator hose on the passenger side infront of the ecu.
That is called a "Duo Valve" or "HVAC Heater Control Valve".
Here is the Mercedes-Benz part number: 0048302084
Here is a link to one, you can search around and might find one cheaper.
Duo Valve HVAC control valve
They also sell a repair kit on amazon. That would be the cheapest way to go.