how to locate AUC file in AX 2012

The location of the file depends on your operating system. Under Windows XP the file will be located under your Local Settings\Application Data folder. Usually, this is as follows:

C:\Documents and Settings\%USERNAME%\Local Settings\Application Data

Under Windows 7 and Windows Vista the file will be located under:

%USERPROFILE%\AppData\Local

 cache file is stored together with the user profile information. And as so it's location varies according to the operating system version used.

You can find it in following folder:
Windows XP and Windows 2003
C:\Documents and Settings\%username%\Local Settings\Application Data

Windows Vista, Windows 7 and Windows 2008
C:\Users\%username%\AppData\Local