Americal fridge freezer service manual Whirlpool G RBB 2V 20/0

Hi, can anyone help with a service manual? replaced defrost heater which was down to earth. Now freezer will not defrost. Bi metallic switch (defrost stat) works. Live to the defrost stat comes from the pcb, question is how/when does the pcb determine defrost output?
is there a way to force a defrost on the control panel?
freezer is 15 years old and has served me well, the problem is its 901mm wide and all the newer models are at least 10mm wider.... i just don't have the room or the energy for her doors nagging about the mess if i have to chase the wall back 20mm!!