Peter R. wrote:
The later model C172s and 182s have an automatic alternate air feature
that will pull air from within the engine cavity if the air intake below
the spinner clogs up.

Don't all planes? It's a prety common feature that the alternate air
door is spring loaded. Pulling the carb heat (or alternate air) knob
will pull the door open, but even without pulling the knob, if the
pressure differential gets too high (i.e. the intake is clogged), the
door will open on its own against spring pressure.