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Parts for Whirlpool ER8YHMXSL01 Refrigerator - AppliancePartsPros.com

I am assuming that the compressor runs all the time except when it is in defrost.

Sounds like you are low on freon.
Be sure that the compressor has run for several hours before checking your coils. If you check them shortly after or during a defrost cycle you could come to the wrong conclusion.

Below is a good link, check out the example pictures about half way down the page.
http://www.applianceaid.com/refrigerator-not-cold-enough.php

If it is low on freon, it will be an expensive repair as you need a pro.
Also there is no use adding freon until the leak is found and fixed.

Often it makes more sense to put those dollars towards a new unit.

I would check the warranty as many units have a longer sealed system warranty.