A digital controller replaces the mechanical thermostat with a small electronic unit and display. It reads an air probe and often an evaporator probe, compares them with the setpoint and switches the compressor, evaporator fans and defrost heaters accordingly. Settings are stored as parameters, set by the manufacturer and adjusted by trained technicians.
The benefits are visible temperature, precise setpoints, programmable defrost, high and low temperature alarms, door-open alarms and, on many models, a record of maximum and minimum temperatures. Some controllers support data logging or connection to a monitoring system, which helps in kitchens with HACCP plans and in pharmacies with temperature-recording requirements.
Controllers need protection from voltage spikes and moisture. In Indian conditions, a good surge protector and sound earthing are wise, and the controller should be mounted where water from cleaning cannot reach it. Staff should be shown how to read the display and acknowledge alarms, but parameter menus are best locked so settings are not changed by accident.