The Sourdillon control is a very unique piece of equipment. It is a combination thermostat (gas & electric), a safety valve, and a power selector, all in one. It's proven to be pretty reliable over the years. The only down side to it is if one part fails, the whole thing has to be changed.
There's no point in going over every aspect of the Sourdillon control. The basics are already covered in Electric Thermostat, Gas Thermostat, and Safety Valve.
The Selector shaft selects between electric, gas, and off positions while being rotated. When in the gas position, it also acts as the plunger for the safety valve. It is what you push in and hold when lighting the gas burner.
One thing to avoid when troubleshooting the Sourdillon control is loosening the two bolts that mount the electrical connection housing. This is where the circuitry to the heat element passes in and out of, enabling it to be controlled by the thermostat. Included in the housing is a micro switch., which is controlled by the thermostat mechanics. The micro switch. is what actually opens and closes the circuit to the heat element. The two bolts mentioned above not only mount the electrical housing, but also hold the micro switch. in just the right place. If you move the micro switch. it is very difficult to reposition properly. If you are in a situation where you have to reposition the micro switch., get the refrigerator down to operating temperature, be sure you're switched to electric, and with an amp meter clamped around one line try setting the micro switch.
Instamatic Innovator. The Instamatic Innovator series and a few Coldstar refrigerators used the Sourdillon control exclusively. The control is mounted to a plate on these models, which is then mounted to the back of the refrigerator. Also mounted on the other side of this plate (hidden) is a micro switch that provides power to the igniter. If you need to pull the Sourdillon control, disconnect 12 volt power from the refrigerator first to prevent a short. When removing the plate, it has to be shifted slightly to the right for the micro switch to clear.