Began having problems with 15+ yr old Kenmore side by side 2-1/2 yrs ago. It started with ice maker which i replaced, but it probably was related to later symptoms of not keeping it cold enough, causing ice and frozen food to melt and temps to rise in fridge up towards room temp.

Each time,(many) we would take / move everything out before it spoiled to another fridge and freezer. Dumping ice drawer, emptying drip pan, wiping the wet out then turning off for an hour allowed it to come back on and work fine for a week or longer. The condenser coils were cleaned of dust / crap multiple times as was fan blades and area.

Thermostat was replaced (several times) because of either an off brand part or I kinked capillary tube on install. It worked for a while, only to repeat the same drill.

Next, the defrost timer was replaced, then the freezer coil heater and thermister. It still failed off and on with weeks, sometimes months in between before we had to do yet another food transfer to secondary refrigerator in the basement. Although the old girl is 36 yrs old, it has never so much as burped, but it is an ugly color.

In May this year, I finally determined the freezer coils were only getting frosty on the bottom two inches or so, indicating low freon. I put a vampire tap on the low refrigerant side and added a R-134 until the pressure was correct. While it was opened up, I removed the thin, metal partition in the back of the freezer covering the coils. I cut a 8" x 12" section out and replaced using double sticky tape to hold a piece of plexiglass in the opening. This allowed me to "see" coils and kept watch to insure they were uniformly frosty over the whole area. Checking every now and then, they remain frosty.

It's been almost 3 months. Every time we take something out of freezer or fridge we regularly check thermometer temps in both freezer and fridge.
They are consistently near 0 and slightly under 40 respectively. The exception is when the door is open for a to load new groceries on a warm day. A temperature recorder also verified temps holding, except for the the defrost cycle which show spike for a couple minutes in the defrost cycle.

As seems to be the case, it picks the worst time to warm up. I had just loaded a cooler with picnic stuff for a church picnic and had the door open for a bit. Both freezer and fridge were also stocked up from shopping trip yesterday. I was heading out the door, running late and my wife said, "hold it, ice is melting and temp in the freezer was 45 and climbing". This meant carrying everything downstairs to the standby refrigerator and I was late to church picnic.

The unit was turned off for an hour or so and back on. Now, an hour or so sine turned on, coils are uniformly frosty (visible through my plexiglass "window"). Temp in the freezer is zero and fridge is 37. Although these are just cheap thermometers, swapping them yields the same temps

Given I've eliminated just about every common fail point, can anyone give me a fresh, new idea? Does this point to the thermostat and possibly the capillary not installed perfectly? If so, why would it work for months and then crap out?

Have we reached the point where I can't breath life into this old horse anymore?