Like a lot of people, my freezer is working fine (food is frozen), but my refrigerator is slightly cool, but not cold. There was a ton of dust underneath and in the back on and around the condenser fan. I cleaned all of that off. Today, i took the back panel off of the freezer, and I saw that the coils (?) inside were covered in frost. I'm assuming that's not normal. I'm going to unplug and defrost entirely. Is there anything else I should be doing?