  The temperature inversion symmetry $R\to \frac{1}{T}$ is studied for the
finite temperature effective potential of the N=1, $d=5$, supersymmetric
$SU(3)_{c}{\times}SU(3)_{w}$ model, on the orbifold $S^{1}/Z_{2}$. For the
value of the Wilson line parameter $\alpha=1$ ($SU(2)_{L}$ breaks to a
$U'(1)$), it is found that the effective potential contains a symmetric part
and an anti-symmetric part under $\xi\to \frac{1}{\xi}$, with, $\xi=RT$. When
$\alpha=0$ (for which, $SU(2)_{L}$ remains unbroken) it is found that the only
contribution to the effective potential that spoils the temperature inversion
symmetry comes from the fermions in the fundamental representation of the gauge
group, with $(+,+)$ or $(-,-)$, $Z_{2}$ parities. This is interesting since it
implies that the bulk effective potential corresponding to models with orbifold
fixed point localized fundamental fermions (and with no bulk fundamental
fermions) has the temperature inversion symmetry.
