To answer the question, presumably it would be below the evaporator. You can lay eyes on the evaporator when changing the cabin filter.
Even if there isn't enough of a plug for it to back up, a restriction may eventually cause an odor. So if
@Sprinkle_Star wants to at least check it, it's a good idea.
USB-C Bore scopes that you can plug into your cell phone can be easily/cheaply had...
https://www.amazon.com/gp/product/B071HYRPND/
I'll continue to peruse the manual to see if there's more detail.
EDIT: No luck. I think it's apart of an assembly that houses the core and that assembly is removed/installed as a unit. So there's no detail on it. Not even sure it's visible in the diagrams of the unit.
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