Refrigerator not freezing

fridge and freezer stay about 50 degrees. Compressor runs all the time. There is frost on the upper portion of the condensor but not on all of it. All fans are working. Can I quickly test the components to determine which one is bad to order? I have test equipment and some electrical knowledge. Any suggestions?

Sounds like you may be low on freon.

Here is a link, see the Example pictures part way down the page.