Follow below steps for enabling archive log mode in oracle RAC.

1. stop the database service.

srvctl stop database -d DBACLASS

2. start the database in mount state.

srvctl start database -d DBACLASS -o mount

3. enable archive log mode.

SQL> alter database archivelog;
Database altered.

4. Restart the database service (using srvctl)

srvctl stop database -d DBACLAS 

srvctl start database -d DBACLAS 

5. set the archive destination to a ASM DISK

SQL> alter system set log_archive_dest_1='LOCATION=+ARCH/' scope=both sid='*';
System altered.



SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            +ARCH
Oldest online log sequence     724
Next log sequence to archive   726
Current log sequence           726

SQL> alter system switch logfile;
System altered.

For disabling archive mode also  . steps are same

srvctl stop database -d DBACLASS
srvctl start database -d DBACLASS -o mount
alter database noarchivelog;
srvctl stop database -d DBACLASS
srvctl start database -d DBACLASS