  Based on extended multicolour CCD photometry of the triple-mode radial
pulsator V823 Cas we studied the properties of the coupling frequencies invoked
by nonlinear processes. Our results support that a resonance connection as
suggested by Antonello & Aikawa (1998) affects the mode coupling behaviour. The
P1/P0 period ratio of V823 Cas has an "out of range" value if compared with the
period ratios of the known double mode pulsators, while the P2/P1 period ratio
is normal. The periods and period ratios cannot be consistently interpret
without conflict with pulsation and/or evolution models. We attempt to
interpret this failure by the suggestion that at present, the periods of V823
Cas are in a transient, resonance affected state, thus do not reflect the true
parameters of the object. The anomalous period change behaviour of the
fundamental and second overtone modes supports this idea. We have also raised
the possibility that a f0 + f2 = 2f1 resonance may act in triple mode
pulsators.
