Another update:

Just now caught the fridge going into a defrost cycle. I had opened up the freezer to check the temp gauge, and hear this hissing and popping (almost like wires shorting). Then I realized it was the heater coil was on and some bits of water were dropping on them.

I checked the pan under/back, and it barely had water in it, and the coils barely had any ice at all on them... so I have NO IDEA why it decided to go into a defrost cycle when it was reading 35 inside!

I guess I should just buy the motherboard and 'see what happens', and if it doesnt fix it, then I'm out more money guh.

At wits end figuring this one out. Read so many issues on the net trying to find anyone with the same odd behavior, so I can know whats wrong.

Issue:

Freezer is about 35°F, but door reads 0°F
Fridge is around 41°F, door reads 38°F
0°/38° is what I normally keep it set at.
Compressor kicks into high gear more often now.

Details:

Almost 2 weeks ago now, the fridge was being louder than normal, like the compressor was kicking into 'Power Freeze' mode (heavier compressor drone than standard light humm). I figured it was due to a bunch of high humidity days, and it was just burning away condensate (not the case apparently).

Last friday (5 days ago), I went into the freezer, and boxed food was soft. It was clearly all of a sudden 'not freezing'. This is when I began my debugging.

After fridge reset (pulling power for 5 minutes), door will read matching temps to my own thermometers... but then after a half hour, door reads the inner temps are matching what I have the control set too. Obviously NOT TRUE.

Compressor still running heavy even though the door says the inner temps match my set temps. So why is it running. Eventually the compressor will idle down, and then shut off. But when it does, the inner temps still are not right.

NO over-ice build up on either side. Just a light frosting on the top 1/4th of each side's coils inside.

Fans seem to run when they run.

Manual-diagnostics reveals no warnings.

Pba Inv Comp light is a steady 'on' which according to the diagram, means all is ok there.

Fix attempts:

I bought (from here) new coil sensors for both fridge and freezer side (sensor from here was too short to install on fridge side though: https://dl.dropboxusercontent.co...fridge-sensor-length.jpg). It didnt solve the issue.

I had also bought one of the top sensors freezer side to replace just in case that one was reading off. Nope.

All sensors (new and old) read about 5.100k Ohms at room temp (75°F).

Going forward:

I don't know what to do. Should I just buy a new Pba (Samsung DA41-00524A Pba Main - AppliancePartsPros.com) and see if that fixes it?

Is this an indicative symptom of some other known problem?

Things for me to test/try?