Hello,

I had some experience repairing both "no-frost" and "simple" fridge-freezers (I'm no professional, but have general knowledge and some tools).

If it is "no-frost" system, then checking fans, air valves, defrosting system is the way to go first.

If it is simple "top_fridge/bottom_freezer", all experience I had was simply fridge not cool enough, and freezer working OK.
This is due to evaporator lines going first through freezer section, and then in less dense manner going through fridge section. If there is a leakage, lack of refrigerant evaporates in freezer section first and only little evaporation happens in fridge section.

But what about the other way around? This does not look like lack of refrigerant?

In this fridge thermostat looks OK:
*if I set it on mid (3), fridge is ~+8degC, but freezer is ~+2degC;
*if I set it on max(7), fridge is ~+1degC, but freezer is ~0degC; Some food freezes inside fridge section.
*Condenser is clean and only slightly warm. System works on 40g of R600a.

Any suggestions on what to look first?