FCOM DSC 27-10-20 has a schematic which may help.
The ELACs compute yaw orders for coordinating turns and damping yaw oscillations, and transmit them to the FACs.
Two electric motors that position the artificial feel unit also trim the rudder. In normal operation, motor N° 1 (controlled by FAC1), powers the trim, and FAC2 with motor N° 2 remains synchronized as a backup.
Something is making a fac produce a yaw order, the problem is finding it.