No audio on FaceTime on iMac (OS 10.13.6) I am not getting any sound on FaceTime.  The picture is fine but audio is neither sent or received.  

How would I troubleshoot this on macOS 10.13.6?
If the audio is not sent there is nothing you can do. It sounds like there is no audio on the other end. I have system 10.13.6 and Facetime works fine for me. Call a friend who has Facetime and see if it works. Maybe the sender has the volume turned off. Also check your volume is turned up.