SGH520 measures the outside temperature and with the help of microcontroller heating period is applied according to the diagram shown ebow.
When ignition key is turned on, the pilot lamp lights and heating starts. Longer heating time in cold conditions and less heating time in warm conditions.
After pilot lamp is off the heating continues for 20 sec more while engine keeps on running. If the engine is started before the pilot lamp is off (not recommended) ,
pilot lamp shuts off and the heating continues for 20 sec more.
For example :
At -20°C pilot lamp on: 40-45 sec > Total heating period: 60-65 sec
At 0°C pilot lamp on: 25-30 sec > Total heating period: 45-50 sec
At +45°C pilot lamp on: 1±0.2 sec > Total heating period: 20±3 sec