Well, I emptied the freezer and took the back panel off, revealing the evaporator... it had significant chunks of ice in it, with significant space around them. It seems to me that it had been frosted over solid at one point, and had semi defrosted at some point before freezing again, but there didn't appear to be any recent build up of frost. Each time the compressor shuts off, the frost on the tubes would melt away nearly completely, the chunks remaining. I would guess that how ever much it defrosted, was not enough to fully defrost it. However, I have my suspicions that the defroster element might have given up the ghost, or the defrost thermostat is malfunctioning in some way. Really though, how many ways can a thermally controlled on/off switch malfunction? Not a lot. I cleaned more strawberry juices out of stuff, (which was surprisingly minimal at that depth) and melted away the remainder of ice with my heatgun on low. I put it back together and loaded the frozens back into it and went to bed. The next morning, it seemed to not be cycling oddly anymore, however, over the last few days, it seems to have gotten back into that routine of a few minutes off, a few minutes on. I think I'm going to have to test the defrost timer, the defrost thermostat, and the defrost element, to make sure they're all working correctly. A light across the defrost thermostat should do the trick there, a wireless thermometer would be good on the coils.. I haven't been able to find any information on what resistance the Heating element should run at, I have tested it, but my meter was reading in the MegOhms.. much higher than I expected.
It would also be nice to know what temperature the defrost thermostat is supposed to open and close at.. Elsewhere, I was able to find that the timer is 6h/21m, though every circuit diagram I've seen, makes no indication which poles of the relay are switched, only that there is a connection between two... Bad form.
What bugs me, though, is why is the cycling so short? it's like a jet of frozen air is hitting the thermostat directly, causing it to quickly cool to shutoff, then warm up quickly to start again.. time to mess with the top/bottom air mix and see what radically changing it will do.
I wonder if I have too much stuff blocking return airflow from the freezer into the evaporator.. that could possibly do the same thing, but it's never been a problem before...