I just got an older model Whirlpool refrigerator which works somewhat. It's not cooling well enough to get things as cold as they are supposed to be. I've checked some help sites and so far removed the cover panel inside the top freezer cover. There was a small amount of frost build up but not like photos in the help sites. It was cold but not freezing cold inside. The fresh food area is cool but not cold. Where should I check from here?