Many fridge / freezer combos use an evaporator fan in the freezer that pushes the cold air into the fridge section. If that fan stops working, the freezer can be cold but the fridge portion will be warmer than normal.
The controls (manual or electric) determine how much air is diverted to the fridge from the freezer to regulate the temperature.
I had the evaporator fan fail in my Whirlpool and it behaved the same way after only one year. The freezer was fine but the cold air was not getting down to the fridge. Once I replaced the evaporator motor, it has worked fine ever since.
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