Dear Panagiotis,
Have you set TYCOn = 0 s and appropriate values of YawSpr and YawDamp in the ServoDyn input file? These are needed to use active yaw control from Bladed-style DLLs.
You can avoid receiving errors about “no valid value of phi” by upgrading AeroDyn v15, as reported in the following forum topic: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence - #2 by Jason.Jonkman.
As you noticed in the source code, avrSWAP(102), avrSWAP(104), avrSWAP(108) etc. are currently ignored by ServoDyn.
Best regards,