The APS-3C and APS-4C controllers utilize the CIT-1 aerial snow sensor, the GIT-1 gutter snow sensor and the SIT-6E pavement snow sensor to detect weather conditions. All three of the sensors work in the same way, they require a temperature below 38 °F (3.33 °C) and moisture on the moisture grid. Both the CIT and GIT have a protruding tube that contains the temperature sensor and the moisture grid is on the opposite side.

In all cases applying moisture (wet sponge/towel) to the moisture grid, and spraying freeze spray on the temperature sensor should turn on the sensor.