No defrost timer is cited anywhere for this unit, just a thermostat, heater element, low voltage board and high voltage board. I take it that the timer is probably incorporated into the low voltage board's circuitry. Anyway, soon I will embark on trying to figure out why I have to rip it open and heat-gun the coils every two or so weeks, as they become a block of frost-like ice. I noticed pointers on testing the thermostat and heater, but can anyone with some expertise make any other recommedations? It's a 1993 side-by-side with the electronic front panel (SXDE27NE). Is there a typical failure point? Is there a simpler way to test the operation of the power boards rather than spending about $100/each and replacing them (yes, that would be AFTER testing the thermostat and heater...). Anything at all - my back is tired of unloading the freezer...

It wasn't clear to me whether you tested the coils or not. That is certainly the place to start. Determine if they can work, given the opportunity. Then the thermostat, make sure it is allows a circuit to be made.

I don't have an easy way to test electronics. Most repairmen just swap in new panels after they rule out mechanical and eletrical problems.

The other question is do you think it is defrosting at all? If so, then the problem might be a clogged drain tube which results in water building up in the freezer and then encasing the heater which then results in frost build-up. See our article about clearing the drain tube.
http://acmehowto.com/howto/applianc...k/draintube.php

I guess because I've had my head in that fridge so many times not all my brain cells are intact. She is draining, for every time I take the heat gun to it I am able to leave a puddle of water underneath the unit like when my dogs were puppies (but they couldn't get under the thing) - I have to melt that much ice as the entire coil unit becomes a pretty solid block, even extending up over some of the wiring, though under the coils and above the drain pan remain clear and dry. I remove the inside back panel and the coils will have had a block of frost appearing ice built up on them causing no chance of air circulation. Because of this the bottom of the freezer is cold, the top area warmer and the regular refrigerator area starts to stink (what was my first clue?).

If you have tested your coils for continuity and the proper resistance and you have tested the thermostat and they check out then either you are not getting current for some electrical related problem, the boards are faulty or there is a defrost timer you have not discovered.

If you've looked at the schematic and know there is no defrost timer and you have ruled out an electrical problem then I think you are left with replacing the electronic control boards.

Do you think that the heater "coil" being corroded all the way through might stand as a good clue as to what is going wrong?... :-)

By George, I think you've got it.