Turn the dial a few notches in either direction and monitor the temp. 0F is the temperature you're shooting for.
This looks like a General Motors product before they sold out their appliance division in 1979. If the name plate on the door states "Product of General Motors USA" it's a pre 1980 model, which is what you want. If you can find the placard with the serial and model number, one of the Frigidaire aficionados here will be able to decode the date for you.