Hi -- I have a 9 yo Kenmore freezer+fridge. It's set up so that the
fridge is cooled by siphoning air off the freezer. The problem is that
the freezer is building frost, blocking the duct, and thereby warming
the fridge. I don't think this is a "frost free" device, so i don't
think it's supposed to defrost itself (although how would I know?).

Normally, perhaps this wouldn't be a big issue, except that I've now
had to defrost it twice in the space of a few weeks. I've googled
around thar intarwebs for advice... here's what I've found:

1) check the seal by closing the door in a dollar bill and seeing if
there's tension. it looked like there's tension all around.
2) Defrost for minimum 24 hours. We didn't wait that long before
because we didn't know if frost was the problem. This time, I'll wait
until tomorrow to plug it in again. But surely that doesn't explain
where all the frost is...
3) I don't open the fridge or freezer very often... so I don't believe
that's my problem. I'm in California, which is pretty dry, although it
has been humid recently. But it's hard for me to believe that's enough
to produce all this frost. I've lived here for several years now, and
none of the other freezers i've used have had this problem (although
maybe they had defrosters).
4) I don't keep a lot of food in my freezer or fridge. Is that a
problem? One fix-it guy I know mumbled something about a lower heat
capacity, but I don't see why that would mean I'd get more frost.
5) I typically keep 3 ice trays in my freezer, and I refill them
often... is it possible that the ice is subliming? Or evaporating?
Enough that is to produce perhaps 1 liter of water from frost?
6) Perhaps, sometimes, I (or a guest) isn't closing a door all the
way... but that seems unlikely since there's a bit of a magnetic
attraction.

Anyway... the point of my post is to see if anybody has any ideas for
things I can try to minimize or slow the growth of the frost... how
help me figure out what to try to fix it. That same fix-it guy from #4
told me to just buy a new one, but that's not worth it for me because
I'm going to (probably) move away this summer.