Funnybone
1. Why isn’t it a psik reisha dnicha lei?
– OF course its nicha lei, You want the compressor to turn on when the fridge gets warm, thats how fridges work. If it doesnt do that you need a new fridge.
2. If it’s lo niche lei, can you rely on it or only Al yidei akum?
– No psik reisha delo nicha lei is not automatically mutar
Meno is right on older fridges where it takes some time for compressor to go on, so not neccerarliy if you open fridge for short while would it trigger the compressor thus it wasnt a psik reisha.
Today though apparently there are all sort of monitor and sensors that are triggered ever tiem door opens, it isnt just the light/compressor.
As for keeping it in Shabbos mode all the time, the manuals all say that ruins the fridge which makes sense, these functions are there for a reason