I just bought it a few days ago, and the compressor has been working since it was hot to 4-5. Why? How to adjust the temperature controller value in summer?

The compressor has to work continuously for more than 8 hours after the refrigerator that has just been bought for a few days is opened to the 4-5 gear. If you work continuously for several days, it means that the refrigerator is out of order. In summer, set the thermostat value at 3-4 according to personal requirements. The mechanical thermostat has a normally open contact. If connected to the normally open contact, the electric compressor will always work. I suggest you ask customer service to check whether there is something wrong with your refrigerator.