If I remember correctly, back in the day when refrigerators were first coming online to the public, the condenser coils were on top of the unit in the pictures I saw.Modern side by side refrigerators are designed with automatic defrost systems controlled by computer processors. Unfortunately, the sensors that monitor box temperatures are usually placed immediately adjacent to the evaporation coils where they can become encased in ice in such situations as when a refrigerator door is left open. In these situations, the processors continue to receive data indicating a cold refrigerator box because the sensor is covered in ice even though the box itself becomes too warm to store food. The only refrigerators that are designed and built for reliability (such as Sub Zero) are inordinately expensive <$15K. Another design factor that would improve the efficiency of consumer grade refrigerators would be to relocate condensation coils and compressors on top of the units. This reduces the accumulation of dust on the coils and components where heat is exchanged. This would also keep warm components above refrigerator boxes so that heat can rise away from the units without passing around the cold areas. This is just my opinion and I’m sticking to it…..