How to Troubleshoot & Replace Whirlpool AP6010261 / WP67001036 Defrost Timer (Refrigerator)

I removed the shelves and the shelf holders, took the back panel off, loosened the evaporator. Removed the heater element and the thermostat. Re-installed the evaporator the back panel, shelve holders and shelves. Then I located the defrost timer in the refrigerator. 

Replaced defrost thermostat and timer. 

I called about possible failure of components and was advised that the issue could be the defrost heater, thermostat, or timer. I was given the information to test existing components. The timer was not required in my unit. I tested the heater coil and thermostat. The thermostat did not pass testing specifications. Replacing the thermostat rectified the problem. Most of my time (two hours) was spent defrosting the evaporator coil so I could access the components for testing. Replacement of the thermostat and replacing all protective covers only took about 30 minutes. Appliance parts pros allowed return of unused purchased components. I paid for return shipping. Seemed fair to me. 

We decided to replace both the thermostat and the timer but I believe the problem was the thermostat. The frost was not exactly obvious until we began to take the unit apart. The repair was quick and easy. It took longer than I would have liked for the fridge to turn back on after the repair so be aware of that and don't worry. Our fridge was a little different than the one in the video but everything went well and the video explained it all. 

I ordered a new Light Switch, Defrost Timer, and Crisper Pan and installed them. 

Replaced defrost timer in about an hour. Saved over $150 on a service call by doing it myself.