  While Carnot's model engines demonstrate ideal performances regarding
conversion efficiency, they cannot be actually used as energy converters since
they are non causal systems. Such an unphysical behavior indeed restrains the
working conditions to a single point where, in the case of a refrigerator
(generator), the cooling power (output power) vanishes. Focusing on the example
of a thermoelectric refrigerator, we study the impact of different dissipation
sources on the causality of such systems. Basing our analysis on the block
diagram description of this system, we discuss particularly the fact that heat
conduction cannot ensure causality.
