I'm not exactly sure I understand what you are saying, but let me try to say it back to you to see if I do. You have different temperatures on the top and bottom shelves of the fridge. You put in 2 computer fans--1 on the top and 1 on the bottom, to mix the air to get a more even temperature. Now the temperatures are even, but the fridge runs for 4 ours and only stops for 10-15 minutes before starting up again? Is that right?
If you are doing this with the fridge empty, putting some things in the fridge will help (water bottles is the normal thing to do). The fans do a few things that affect how the fridge functions.: First, they increase the heat transfer from the outside of the fridge to the inside (moving air feels colder or hotter to our bodies than it actually is because of how quickly it removes or adds heat to us). Second, they increase the response time of the sensor (the sensor "knows" what temperature is in the fridge faster). Third, they actually add some heat to the fridge (probably not much, but some) because all the energy they use to move the air around eventually shows up as heat. By adding some thermal mass (bottles of water or cheese), the fridge will run longer to get down to the right temperature, but then it should stay off for longer, too, because the thermal mass will help keep things cold longer.
What's the temperature in your home? If it's too hot, that could cause problems too. I had a friend who told me about "Russian heat" that was just on all the time and he had to open windows when it got too hot in the winter. If that's the case in your home, it could be overworking the fridge.