On NS Employee Time Tables there is a list of locomotives sorted by group depending on how they are rated for tonnage. They're all pretty straight foward, but there is a reference to a "C-90-AC" that I am not familiar with and I can't turn up anything on Google about it other than things referencing back to an NS ETT. It's grouped with other GE AC units and it is not a different name for the SD90MAC as that is listed as a separate entry. So what is it?