Lint and dirt should be cleaned from the refrigerator coils every six months to a year—and more often if there are pets in the home.

When coils are coated with lint, dust or pet hair, your refrigerator works harder than it’s designed to, which can prevent the appliance from cooling properly and efficiently. The additional work can increase the energy costs of the refrigerator by as much as 35% and shorten the life of the appliance.

Source: energy.gov