those little ports are to drain off the condensate builds up from when the warm, moist air from the kitchen enters the cold, dry air inside the fridge when the door opens
frost free freezers have little heater elements that come on when in defrost mode i think, then the water drains out the back the same as with fridges, and onto a tray that sits above the warm compressor and evaporates
What I meant was with the frost free ones (and I thought the condensate wasn't just about warm air from the kitchen - or in my case, artic air from the garage - there'd also be the potential of condensate due to what was going on with the frost-free / auto defrost thing) - there wasn't the same degree of "closed system" in terms of the air - perhaps with the refirgerant gases - I mean who'd want them venting, eh - well maybe a little, just to top off the booze.
And there's also a fair point by Pyro Tim, heat will radiate out in terms of how the compressor is chilling the fridge. The frost-free ones just add a bit to that, 'cos mostly they add a little heat into the system to do the defrosting (either that, or cheat a bit with reusing some of the heat produced, rather ironically, to chill).
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