Brewtoo: The Mercedes service CD discusses removing the expansion valve from the old evaporator and transferring it to the new evaporator, prior to installing it as a unit. I'm sure you could do it after the fact as well, but I'm happy it came preassembled. BTW, the new evaporator includes a large 3x5 inch rubber seal mounted on the dashboard side of the expansion valve that apparently seals up a substantial hole in the firewall where the expansion valve protrudes. Hopefully, that means there is room to manuever the unit around a bit.