AutoCAD MEP

[#1]

I am using AutoCAD MEP 2012.  Is there a command that will generate an Isometric one line drawing from an already created 3-Dimensional drawing?

[#2]

There is not a command to generate a isometric drawing from a 3D model.  But what you can do is put your model into an isometric view and change your display representation to a display that forces pipe to display as single line. 

It does take some manipulation of the display system in order to make it work but a "reasonable" isometric drawing can be created.  I like to create container drawings that xref in my model so I can use xclip in order to logically break my isometric drawings up.  That way I do not have my complete model as one isometric but several isometric drawings that represent the complete design.  The project management system is of benefit when using this method.