Air from the freezer is blown into the fridge by a fan, some new type frigs have electronic controls that open and close a vent to frig. the older ones have two vents in the frig from the freezer and when covered with frost or ice the air will not reach the frig. check for ice or just defrost the freezer if there is ice or frost, also check for food or plastic over vents in freezer. Also check that the freezer fan is running as these sometimes become blocked or defective motor.