If the refrigerator is arranged in the modern way using a "remote" cooling element with a fan circulating the air within the cabinet past that element then, even if the cooling circuit works properly, you may have a fan problem. As you open the cabinet you should hear a fan stop turning, it will then start up again as you close the door. Even if you hear a motor stop and restart, it is important that the impeller turns with it - you need to hear the "air hum" as well as just the fainter motor hum. I once suffered a impeller detachment so that even though the motor still turned the impeller did nothing much - I had to buy a new impeller that gripped the motor axle properly. You need to check both: Cooling circuit actually cooling adequately, and that the air circulation within the cabinet works correctly. The model and age of your fridge is important information for people to be able to advise you more precisely.