The clutch doesn't hum. Did you go through the commissioning procedures with the AC12? One of the first things it does is go through a process where it figures out what type of drive you have and how to operate it. Without doing this, it may not be sending the correct polarity or voltage to the drive.
To test the drive, just disconnect it pull the arm out half way and touch the leads to a battery
- it will move one way or the other if working. Don't let it drive past its stops.
Frankly, if the autopilot
is important to you and your sailing, and you have a new computer, etc, I wouldn't be installing an unknown, at least 14yr old (Raymarine has owned Raytheon
that long) drive unit that came with a boat with shot electronics