No, the SC-40C does not use a snow sensor, it is completely controlled by the attached APS-4C. However, the SC-40C does require the High-Temperature sensor Thermistor to be connected (or bypassed with a 470K-ohm resistor) in order for the unit to operate. The SC-40C only acts to extend the load capabilities allowing you to energize a larger heater area off a APS-4C unit.

Click here to view the APS-C series manual

SC-40C, APS-4C and snow sensor digram