A mechanical thermostat has a thin capillary tube filled with a gas or liquid that expands and contracts with temperature. As the cabinet warms, pressure in the tube rises, pushing on bellows that close a switch and start the compressor. When the cabinet cools enough, the switch opens and the compressor stops. The dial usually shows numbers such as 1 to 7 rather than actual degrees.
Mechanical thermostats are cheap, robust and tolerant of voltage fluctuations, which is why they remain common on chest freezers and basic cabinets. Their weakness is precision. The dial does not show the actual temperature, the switching band is fixed or only roughly adjustable, and the sensing tube can be knocked or kinked during cleaning.
If you have a cabinet with a numbered dial, use a separate thermometer to find the dial position that gives the right temperature, and mark it. Staff turning the dial to maximum on a hot day, then forgetting it, is a common reason for frozen lettuce and wasted electricity.