Manual failover of AAG in SQL Server 2012
Do not use Failover Cluster Manager for your failovers. It can cause problems.


  Do not use the Failover Cluster Manager to move availability groups to
  different nodes or to fail over availability groups. The Failover
  Cluster Manager is not aware of the synchronization status of the
  availability replicas, and doing so can lead to extended downtime. You
  must use Transact-SQL or SQL Server Management Studio.