The smell is probably from mold. Same type of smell as when carpet gets wet, wasn't dried properly and room is not aired properly. Mold grows well in hot humid environments, ie SG. It will probably be less active in temperate countries like China or Korea where weather is cool and dry most of the year. You trap so much dirt in the filter, bacteria and mold will definitely grow in moist dirty environment. The mold will emit VOCs that is the cause of the smell. It will not be in concentrations high enough to harm our health though.
I doubt it is from mold, as
1. I noted other forumers also complained about the "chinese medicine smell" fr AP. Mine is the same, and not moldy smell.
2. I don't have carpet in my rooms.
3. AP are used daily, not stored for a long period then take out and use.
4. After changing the filter, the AP operates in the same location same room. But the Dec 2015 new (original) filters has yet to give out smell, though vision inspection lately shows it is about 1/2 as dirty as those original filters what I throw away in Dec 2015, and there are many raining days in Jan 2016. Those throw away filter started to give that chinese medicine smell after 2 weeks of use, from Aug 2015 (hot month, haze, not much rain).
I must add: I did tried to "troubleshoot" the smelling issue, even wash (separated) AC layers with water first, then next tried detergent; airing & sunning the filters etc does not help too.
I am not sure if it is the particles/residuals in the air, or their reaction to the filter or the coated chemicals on the fitler, or whatever. But I am quit sure it is not the mold.
The mesh does trap a lot of the grease. If you clean it after a season of heavy cooking you will know how much grease is in there. Gotta soak in hot water plus degreaser. The AC is to reduce the cooking smell when the hood recirculates the air back into the kitchen, since we usually don't have hoods that vent to the outside, it won't really remove the smell totally.
