FileInfo.com


.AC$ File Extension


File Type AutoCAD Temporary File
File Format File
Common? No
File Description Temporary file generated by AutoCAD, a 2D/3D drawing and design program; contains information used by various commands, including "UNDO" and "HIDDEN LINES."

AC$ files do not contain any drawing data and only exist when AutoCAD is open; they are automatically deleted when the program is closed.
Program(s) that open ac$ files Windows: Autodesk AutoCAD

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/ac$