ARCHIVELOG/NOARCHIVELOG mode transition is a little different in a RAC db than a standalone db.
You can see a transition example below;
11G NOARCHIVELOG to ARCHIVELOG mode transition
[DDD1]/u01/app/oracle/admin $ sqlplus / as sysdba
SQL> alter system set log_archive_dest_1= 'LOCATION=+ARCHIVE' scope=SPFILE sid='*';
SQL> alter system set log_archive_format = 'ddd_%t_%s_%r.arc' scope=SPFILE sid='*';