Hi

I think you have a  typo. Several values of one attribute have to be separated by a semikolon, vut in the first attribute you have a comma

Not: 
ref_ac_columns=u_business_unit,name;code,ref_ac_columns_search=true,ref_auto_completer=AJAXTableCompleter

Correct:
ref_ac_columns=u_business_unit;name;code,ref_ac_columns_search=true,ref_auto_completer=AJAXTableCompleter

The rest looks fine. Check https://docs.servicenow.com/en-US/bundle/sandiego-platform-administration/page/administer/reference-... for more information

Maik