I have made further modifications to the AHU in my Innova to significantly reduce outside air from entering the cabin. I have successfully fixed the rear A/C several months earlier (see previous posts) and this time, I focused on the front A/C.
The problem is, even with the Recirculation mode turned ON, there's still significant amount of outside air going in.
Encircled here is the ducting that brings in outside air into the cabin. (Not my picture).
This is what it looks like when looking inside from the cabin air filter hole (behind the glove box)...
Recirculation ON:
Recirculation OFF:
Even with the Recirculation mode turned ON, the recirculation flap does not provide enough snugness to close the outside air duct. Because of that, significant amount of outside air and dirt seeps through the gaps and onto the cabin air filter. When I checked my cabin filter a few days ago, it was almost black with soot. Considering that my Innova is just 10 months old and I always have the Recirculation mode turned ON.
The picture below shows just how much dirt gets through from the outside. This is also the reason I smell exhaust gases from the outside and why there's fine dust and soot everywhere inside the cabin.
So what I did was, I stuffed the intake duct with aircon filter refill material, similar to the picture below.
Doing this has helped significantly cut down the flow of outside air going in. The filter just restricts air coming in so there's no danger of suffocating. When air does enter, it will have to go through thick/folded layers of this filter. By the time it reaches the actual cabin filter, it's pretty much already clean.