Problem monitoring RAC

Hi, I've some problems on monitoring RAC referring to the SERVICE_NAME of the RAC instead of going to the single instance. I get this error:

Unable to connect to Oracle Server.
Error Message:
Listener refused the connection with the following error: ORA-12505, TNS:listener does not currently know of SID given in connect descriptor The Connection descriptor used by the client was: (DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=virtualipaddress) (PORT=1521)))(CONNECT_DATA=(SID=servicename)(SERVER=DEDICATED)))

From what I've tried in the past I was never able to connect to a RAC using "SID=" but I need to use SERVICE_NAME=
With SID I'm normally able to connect to the single RAC instance but if the server with that instance is down I cannot connect to it.
Anyone had this problem and solved it in some way?