The bad smell inside the cabin is caused by dirty A/C filter.
Take out the filter from its casing. The filter is dirty, black in color.
I bought a new filter. Cost me RM26. Much lower quality but i want to try it anyway since this part is not a safety part and is considered cheap enough for me. The paper material is soften than OEM. Actually, used to survey the filter at Autobacs Klang Sentral last week. Priced at RM165, branded PIAA. Must be a good quality in term of filtering a dust & material, but to me its very expensive. Can`t afford the filter. Below, photos of filter which i bought at one of my favourite spare part shop at Batu Pahat this morning.
The OEM filter (dirty) vs new filter.