I believe you have hit the nail on the head. The temprature controller is not working properly. Not the one in the freezer but the one in the main compartment. It is sometimes refered to as the thermostat.
Basicly the unit has shorted itself and is locked in the coldest setting.
Changing the controller (thermostat) should solve the problem. The part should be available at your local appliance center, or If you like I can locate one for you on line.
If that is the case then that unit is what needs to be changed.
The control on the right goes to an electrical device under the cover that you will need to replace. This is what determins whether the unit cools or not.
The part is available from this web site. It retails for aproximatly $60.00. The part number is XXXXX
Yes it is one of the componants. It is the componant that the temprature control knob attaches to.