The freeze sesnsor is a thermistor temperature sensor that sends signals to the control board.
One end is connected to the evaporator coil, the other to the control board. If the thermistor senses the evaporator coils are freezing over during operation, the control board will shut off the air conditioner, requiring you to manually turn the A/C off and back on from the thermostat.
Dometic A/C Units: 579, 590,591, 595, 600, and 630 series
3109409.001 Freeze Sensor