I have a ~18 month old refrigerator (a Whirlpool, french doors, similar to this model). About two months ago we found that the freezer had largely thawed (as in, all of the food in it was thawed, ice cream melting out of the tub, ice packs not solid), and the refrigerator was over temp by several degrees; at the time the fridge was ~43-44 degrees in the morning at first check (before it was opened at all), eventually it hit more like 47-48. The back of the freezer (behind the drawers) had significant amounts of visible ice, but the vents didn't seem blocked, though it seems like they must have been if there was a lot of ice along the freezer wall but nothing else frozen...
We called a repairperson, and he came and suggested that the thermistat that controled the defrost cycle was the issue. After fully defrosting the fridge/freezer (leaving it unplugged for two days), he replaced it, and it worked fine for ~2 months. I say okay, because the refrigerated section never really was as cold as we wanted; we set it to 34, and that let it get to 38 to 39, which was close (we prefer 37).
About two weeks ago, we found the freezer thawed again with ice on the back and the fridge at 41. I emptied the freezer but took no other action; after three to four days, the freezer was able to hold temperature again and the refrigerator back to 39. This held for about two weeks; yesterday it was again thawed and 41 in the refrigerator, though.
Does it sound like there are still defrost cycle issues here (and the main board needs replacing and/or another new thermostat), or is there something else going on here? Are there any steps I can take before calling for service again?
I will note that I've been a bit concerned about the placement of the fridge in terms of ability to release heat - it's nearly fully enclosed by cabinet on one side, back wall on one side, and a thin cabinet-matching wood board on the third side, plus on top more cabinet-matching trim. There's a few inches clearance in each direction but that's it. The repairman didn't have any objections to the setup and thought it was fine, but I'm wondering if we need to figure out some way to get it some more air? Or is this no longer really a problem with modern refrigerators? Does this sort of problem match this type of cause?