The Turn Double Line and 3D Layers Off command turns the double line and 3D ductwork layers off.
To turn double lines and 3D ductwork layers off, go to
Ribbon: DM HVAC->Layers-> 
Turn Double Line and 3D Layers Off
Pulldown Menu: DM HVAC->Layer Management->Turn Double Line and 3D Layers Off
The double line and 3D ductwork layers will be turned off and not visible on the drawing.
If this command is run while in a paper space viewport, the VP Freeze setting for the layers will be changed to Frozen.