t's a 1967 model, I'm sure other forum members have also noticed the Kitchen Aid KDS-15 next to it. I'd say it's also from the same time period.
I have never owned a Frigidaire bottom freezer refrigerator made after 1965 but I know that by 1966, many of the top-freezer models switched from having the thermostatic damper that Norgeway is talking about to a manual damper that adjusts with a knob. Is there just one or two cold control knobs? I guess there are two. One of them has the "off" position, that's the main cold control. The other one just moves a damper to increase or decrease the airflow in the refrigerator section.
My guess is that the damper is linked to the one you pictured which says "freezer cold control". If you want to make a test, feel the air flow in the refrigerator section next to the air distribution register (probably behind the light shield in the center) while holding the light switch as if the door was closed and see in which direction you get the maximum airflow to the refrigerator. It should be the at the "warmer" setting if I understand correctly how your damper and thermostat work, that will get the most cold airflow to the refrigerator section and it will make the freezer less cold. Then I don't know where you set the other thermostat but you want to have it in the coldest position which should be "3". Check the temperatures simultaneously in both the freezer and refrigerator sections to see how it does before and after moving the controls.
Some refrigerators have two blowers linked to cold controls rather than a single blower and a damper. I'm not 100% sure about how yours is but that knob seems to be the kind they used for damper doors.
Does the compressor runs almost constantly or does it often cycles off? These should run constantly a few hours after the defrost period and then cycle on and off.
This fridge is probably one of the very first models that didn't have a defrost timer that defrosted it at fixed intervals. Instead, it defrosted "as necessary" like today's fridges. At least the 1968 version of your fridge does that. I wish I had the 1967 manual to help you more.
I can't say it's a highly valuable appliance (very few are!) but if it was mine, I'd certainly try to keep it working!
You won't find another one like it easily!