KitchenAid KBFS22EWMS7 Not Defrosting

[TrilliumLn]

Hi everybody,

I have a KitchenAid KBFS22EWMS7 that is not defrosting. I first noticed this problem when the refrigerator wasn’t cooling but the freezer was. I did some initial research and it looked like a problem with the defrost system. I replaced the thermostat and everything was fine for a couple of months. The problem repeated so I replaced the entire wiring harness. Just like the time before it worked for a couple of month, but now I’m back to iceberg status. My initial philosophy was start with the simplest solution, but that hasn’t worked. I’m ready to repair again but don’t want to do a fourth fix, so I’m hoping I can get some more in depth diagnostic advice. 
 

It’s looking like this problem can be caused by the following:

- bad thermostat

- bad defrost heating element

- bad air diverter assembly

- bad control board

- possible other components?

Once the list of possibilities is complete I’m wondering how to test each component. I have a multimeter and some other basic tools. I wasn’t sure if the thermostat is normally open or normally closed, so I’m hoping the forum can help me with this process. I’d like to keep it running so long as the parts don’t cost me a large percentage of a new unit, which isn’t really in the budget.
 

The fridge is now empty and unplugged. Where should I start? 

[TrilliumLn]

Anybody have any advice for testing components?