The carnot efficiency of the refrigerator is simply given by Tl/(Th-Tl). Let's say we have a freezer and ambient temperature of 20 and 28 degrees celsius. I varied the ambient temperature by plus minus 1 degree and found out that the COP varied by about 4 to 5 units. I've read about refrigerators having different climate classes, but how then are refrigerators designed to handle the different ambient temperatures in climatic countries? What is the difference between a refrigerator meant to operate in let's say a tropical country compared to somewhere in UK?