  We present a detailed study of the Nernst effect N$_{zx}$ in
(TMTSF)$_2$PF$_6$ as a function of temperature, magnetic field magnitude and
direction and pressure. As previously reported there is a large resonant-like
structure as the magnetic field is rotated through crystallographic directions,
the Lebed Magic Angles. These Nernst effect resonances strongly suggest that
the transport of the system is effectively ``coherent'' only in
crystallographic planes along or close to the applied field direction. We also
present analytical and numerical calculations of the conductivity and
thermoelectric tensors for (TMTSF)$_2$PF$_6$, based on a Boltzmann transport
model within the semi-classical approximation. The Boltzmann transport
calculation fails to describe the experiment data. We suggest that the answer
may lie in field induced decoupling of the strongly correlated chains.
