When the 'frost free' part of the fridge fails it will literally eventually freeze onto a solid block of ice on the interior of the freezer portion of the fridge, just from the moisture in the environment. So, if it's an 'unclog it once and it's good for years' thing then you're probably spot on. If it's an 'unthaw it once that have it freeze solid again in weeks or months, model and humidity depending', thing than it is probably some component in the chain of things responsible for the 'frost free' billing of the freezer. In that case either wait, or use heat from a hair dryer or heat gun after you open it up, but you'll need a repair or a new fridge. In the latter case it's just not a drainage issue...
'Frost-free' simply hides the ice, but it is there. Auto-defrost makes that ice/frost melt because the freeze cycle is automatically (and frequently) suspended for a short-time. There may or may not be an additional heat-element involved in the melting.
If we rule out pouring water onto the cooling coils, there is no moisture source to produce ice except environmental moisture, whether inside or outside the fridge. So the meltwater—which is now environmental moisture — must be removed to somewhere, and the drain-hole and tube leading from it take that water to a pan that's cleverly placed where the hot coils on the bottom/back of the fridge will speedily evaporate it. If that drainage fails, the same water just re-freezes in place as soon as the autodefrost cycle is over. And if that Ice Age continues and the glaciers expand, eventually safety overrides shut down the unit, possibly forever, and temperatures rise.
Until you know from
actual testing that the drain is running free and from
careful observation that there is nothing present that could clog it, the possibility of the same-old same-old can't be ruled out and the probability remains high.
—paraphrasing the sainted Steve Brennan, of Brennan's Appliance Repair and late of CBC's Radio Noon as best I can recall. He often went on to describe exposing innards and ice-floes to hair-dryers as you have, for the purpose of achieving and verifying those two Necessary Conditions.
