Where is Connection String Located as it relates to Availability Group Listeners?
If you've set-up an Always On Availability Group Listener (and you should), then you'll have a new virtual name to use in your connection string. So if your SQL Servers are SQL01 and SQL02, and there's an availability group called SQLAG01 - then you'll specify this. You could continue to specify SQL01 in your connection string, but if the Always On Availability Group has failed over to SQL02, it won't work. But if you specify the listener name, all will be well.

Make sure that you've got the latest SQL Server Native Client drivers installed so that you can use the extra settings like Multisubnetfailover and potentially ReadIntent