When you HVAC fan on with AC and heat off, does it go past evaporator?

If you switch AC and heating off but put fan on, does it mean clean air gets pulled and put in cabin while staying separate from the evaporator? Or does this air pass by the evaporator then go into the cabin?

My issue is that my AC and the heater is off yet the smell comes through when you put the fan on. This make me think it has nothing to do with the evaporator as I’m assuming when only the fan is on, AC and heat is off, the air does not go past the evaporator?

Also when I first recently changed the cabin filter and put the fan on alone it was giving clean air past week. However yesterday I put heating and AC on, then after switching off, the fan alone, AC off, heat off is giving a bad smell.

Why would that have happened when the fan was giving clean air and does this suggest no problem with evaporator area but smell origin is elsewhere?