This article from Mother Earth News is actually from the mid-80s, but it still makes some points that, if anything, are more valid today. Remember, Mother knows best... Some comments after the jump...
Triple Your Refrigerator's Life Span
Perform these quick, once-a-year home-maintenance tasks to add life to your cooling kitchen appliance.
According to Leroy Richter, former director of THE MOTHER EARTH NEWS Eco-Village and refrigeration and heating instructor at a local technical school, proper maintenance of a modern refrigerator can extend its life from barely longer than the 5 year warranty period to 15 or even 20 years. But wait. You say you have an old one out in the garage that's gone 30 years without a bit of attention? Why shouldn't your new fridge—the convenient side-by-side with ice maker—last at least that long?
Read more:
In Ted's opinion:
Modern appliances generally have a useful design life of 5 - 8 years. In addition to some of the issues raised in the article, modern designs emphasize energy efficiency and useful interior capacity. When I was growing up, my parents had a refrigerator with evaporator coils on the to and a compressor motor about the size of the motor in a Prius. Modern compressor motors are about the size of 3 hockey pucks stacked and use about 30% of the electricity. They also have a 1 year warranty instead of a 5 year warranty.
In addition to keeping the compressor coils clean, it is important to make sure that the door seals are flexible and flat. You should be able to feel the suction when you open a refrigerator or freezer door. Compressors aren't designed for continuous operation. In fact, they should run no more than 5 - 15% of the time, depending on usage. If it is cycling on and off frequently, you probably have a leak. If it stays on for long periods, your coils are clogged or you have lost refrigerant, hopefully the former.
If you service your reefer regularly (especially if you have pets) you should be able to double this. Tripling it seems optimistic to me...