Also many newer high efficiency units do not last as long as older units and the Energy Rating does not include the energy used to make and then scrap a unit. "
Scrapping a unit is a tiny amount of its environmental footprint. The reason for this is the cost to recycle is small and most of the materials are reusable save for the insulation and maybe plastic interior parts. Yes it's true there are many units that do not last as long. However, that's a luck of the draw either because of poor engineering choices or some other issues. Meanwhile, I have purchased/picked up used refrigerators off craigslist that are over 10 years old and they're obviously still working. Any device that saves enough energy to pay for itself is a green solution both for wallet and environment.
If a refrigerator uses so much energy that I could literally purchase a new refrigerator to replace it every single year and break even, then that old unit IMO should be recycled. If the payback is over 10 years, I would definitely NOT replace the unit as that's the general life expectancy with anything after a bonus. I generally don't like buying new appliances because of the uncertainty of its longevity. Getting used ones means saving money and knowing whether or not the unit you got was a dud/had a bunch of known failures or not. Replacing a defrost timer would save far more energy than changing the lightbulbs in a refrigerator. The defrost mechanism isn't nearly as advanced as the whirlpool stuff with the adaptive defrost control so I figured at the very least, I'd increase the defrost interval. One frustration I had with a Subzero refrigerator is that they shipped with a 24 hour defrost interval but their replacement parts in their guide show only 6 hour interval. I'd like a 24 hour interval because in my area, air is very dry so having a frequent defrost interval is unnecessary and wasteful.