How do I replace the defrost thermostat in an Amana refrigerator?

I have an Amana top freezer refrigerator, model TJ22KW that has stopped defrosting. I have done extensive testing and determined that the defrost thermostat is defective. It heats for about 1 or 2 minutes on each cycle and then cuts off.

My question is how do I remove the evaporator cover to get to the thermostat? Does the plastic around the doors just snap out? Do I need any special tools? Do I go in through the bottom of the freezer or the top of the refrigerator?

Any help will be appreciated.

G.M. Durrence (to reply remove -nospam from address)

first, what "extensive testing" did you do? How do you know this about one to two minutes?

I really wonder about your diagnosis. I've replaced those thermostats, but would like to know how you got to that point of view.