First of all, it is not necessary to place the food near the cold air inlet, since they will freeze to receive the direct cold. As for the knob that is in the freezer, what it does is send the freezer cooler or cooler to the refrigerator. If the refrigerator cools a lot, you have to reduce the amount of cold that goes to the refrigerator, moving the knob to the right, which corresponds to the minimum refrigerator. In this case, what is done is to send the freezer cooler, and consequently less cold to the refrigerator. If it is the other way around, that is, the freezer cools a lot and the refrigerator cools little, you have to run the knob to the left, minimum freezer, which corresponds to maximum refrigerator. The normal position would be the knob in the middle (optimal), but it is not always the case, since it varies greatly between summer and winter. Ideally, the temperature of the refrigerator and freezer with thermometer should be controlled. I have the freezer at -18 ºC and the refrigerator at 5 º C. Logically the refrigerators that have freezer temperature control and refrigerator on the door display, no thermometer is needed. Models A and B, have the display on the door to regulate the temperature of the refrigerator only. Model C has a mechanical knob to control the temperature of the refrigerator, but all three models have the knob in the freezer to control the temperature of the freezer and refrigerator.