Frost free fridge freezers have a fan built in, or at least some do - that's as well as the large fan to pass external air across the heat exchange. The fan was

Frost free fridge freezers have a fan built in, or at least some do - that's as well as the large fan to pass external air across the heat exchange. The fan was near the freezer heat exchange coils on the one I dug into. The fan turned off when you opened the door, so you couldn't detect airflow, but operate the door switch and you could, but not where you might think, and it was barely audible. Opening the freezer door made it much clearer. The visible vent in the fridge was the passive air exit, the fan assisted entry vent was hidden amongst the bulge that contained electronics, thermostat, and a flap that shut off the entry vent from the freezer section. Presumably to shut off fridge cooling when freezer was still calling for more. Edit: I should add it was moving a pretty low volume of air, nothing like you might expect from various CPU and case fans.