KitchenAid side by side frigde side is not cooling

Hi,
The fridge side is not cooling and I found that there is some icing on the side where the switch for vegetable/meat bins at. I read the post but did not find my model so I am not sure where the following items are at:

Defrost Timer
Defrost Heater
Defrost Thermalstat

Also, could you tell me how to remove the air diffuser up on top left corner in way in the back?

Thanks

Tai