when should fan be working
I noticed there are 2 fans on the extruder, one on the side and one of the front. The one on the side is turning all the time. The one on the front not. When should the one on the front be turning ?
That depends on your slicer settings. The one on the side is to keep the hot end heat shunt cool so it runs all the time. The one on the front is your filament cooling fan.
If you are running Prusa Slicer or SlicerPE and printing PLA then the fan will be off for the first layer and on for the second and subsequent layers. This all depends on the setting you have though. If in Slicer then look under Filament settings > Cooling.