I have a Welbilt refrigerator, more than 17 years old, and a thermometer I placed inside it reads well into the 40s and lower 50s on really hot days. Temperatures higher than 40 degrees pose a risk of food contamination and even poisoning. I am concerned, needless to say. The temperature control is on a dial, and is graded 0 through 7. Is 7 the maximum cool or the minimum cool?