Any or all of your ideas will help, it largely depends on your climate and how long of a below freezing stretch you can expect. The drain outlet is supposed to be within some distance of the ground, 18" I believe, which is why it was configured that way. In areas subject to freezing, all piping carrying water should be run as far as practical inside the heated envelope, so the drop to within some distance of ground should have been done inside. If possible, rerouting the run inside, with only a very short run outside should solve the problem.
As BMitch suggests, routing the drain through trap would comply with plumbing codes and is the best solution.
Shortening the pipe could fix the problem entirely since the water may not have time to freeze. In frigid climates though, any water outside will freeze. The high outlet could damage you outside wall finish and be an annoyance to passers by.
Widening the pipe will require more build up before blockage, so if the freeze periods are not too long, this could work. In frigid climates, it will still block up eventually.
Insulating the pipe would probably be all that's needed, it has the same effect as shortening the pipe, without wall damage. Actively heating the pipe would certainly work, but is probably only needed in extreme cases. Heat tape that wraps around the pipe and is plugged in to an outlet, with a thermostat to turn off the current above freezing is a common hardware store item in cold climates.
You only have to worry about the attic if it gets below freezing in there. Attics, though ventilated with outside air, tend to stay a fair bit warmer than the outside. I would guess that unless you have good runs of outside temperatures consistently below 0F(-18C), you shouldn't have a freezing problem in your attic.
I'm not sure, but I suspect there is not an override. A blocked drain can cause significant problems if the furnace continues to run. By shutting off the heat, it is good incentive for the owner to solve the problem.
Freezers aren't really designed to freeze things, they're designed to keep things frozen. To change one pound of 32°F ice to 31°F ice, requires the removal of .5 BTUs. To change one pound of 32°F water, to 32°F ice, requires 144 BTUs. Therefore, it requires far less energy to keep an item frozen, than it does to freeze the item in the first place.
Almost all sources (including the USDA) agree that a freezer should be kept at 0°F (-18°C), to store frozen foods. Though a temperature of -5 to -10, is recommended to freeze food.
If the back panel of the freezer is popping off, you might want to investigate what is causing it to pop off. If there is ice forming that is causing the panel to pop off, it could mean that the refrigerant in the system is low, and there may be a leak. This is probably a unlikely scenario, though it is possible.
The more likely cause, is poor air flow.
If there's not good air flow through the condenser, the heat removed from the refrigerated compartments will not be removed from the refrigerant. At the same time, if the air flow through the evaporator is poor, heat will not be removed from the refrigerated compartments effectively. Maintaining good air flow within the refrigerated compartments is also important. The cooled air needs to move throughout the compartment, so heat can be taken away.
- Make sure the condenser fan is working, and there's not a lot of dust and debris obstructing the flow of air across the condenser.
- Make sure there's good air flow across the evaporator, and that the evaporator is not icing over (this may require disassembly of part of the refrigerator).
- Make sure there's good air flow within the freezer, and that items are not blocking the vents.
Best Answer
There should be a rubber drain line that goes from the bottom of the condensate tray in the back of the freezer (probably behind an access panel), out the bottom of the refig, to the drain pan that's under the refrig. That drain line can get clogged with dust/dirt or spider webs. When this happens, the water can't flow out of the freezer, backs up into the freezer, and freezes.
You need to get to that rubber drain tube and clear it out. But first you have to get rid of the ice that's blocking it.
There should be information on line as to how to do this for your particular model refrigerator. On some you can access this from the freezer comparment. But on others you need to in through the back of the refrig to get to the drain line.
Added Picture
Here is picture from https://www.applianceblog.com, that shows the condensate pan on a typical Samsung freezer, showing the ice buildup that results from a clogged drain tube. The drain tube comes out in the center (usually) of the pan that's covered in ice in that picture.