There are several models to choose from starting with the PSK201 with simple logic and wiring (for base compressor and defrost control) to the PSK214 with multiple I/Os and evaporator fan management (for complex compressor, defrost and fan control).
A quick glance at the 3-1/2 digit display panel during operation shows the refrigerator status; which includes an alarm icon and temperature of the controlled space. Depending on the model, defrost control is handled by compressor stop or time/temperature based off of a real time clock.