The FreeSpace property indicates the space available in the paging file. The operating system can enlarge the paging file ...

The FreeSpace property indicates the space available in the paging file. The operating system can enlarge the paging file as necessary up to the limit imposed by the user.  This member shows the difference between the size of current committed memory and the current size of the paging file - it does not show the largest possible size of the paging file.  
This property has been deprecated in favor of a corresponding property(s) contained in the Win32_PageFileUsage and//or the Win32_PageFileSetting.