The SC3D is a micro-processor based solar controller used to heat a pool or spa from a solar collector. The controller senses the temperature on the roof and the temperature of the pool.
If the roof temperature rises 7 degrees above the pool temperature and the pool temperature is below the set point then the controller will switch power to the solar pump which then cycles the pool water through the collector to heat and return it to the pool.
If the pool temperature rises to the set point or the roof temperature falls to within 2 degrees of the pool water the controller will switch power off to the solar pump.