odd smell from AC only when compressor isn't running

[Suprnova74]

So on our first long trip, the bedroom AC compressor wasn't turning on. It was a broken red wire behind the thermostat. I noticed a not-so-pleasant smell from inside the wall when I had the thermostat off. Slightly wood-product-ish I'm guessing form the unfinished luan/fiberboard used for the walls.

Anyway, we typically leave the fan set to ON for a bit of background noise when sleeping and whenever the compressor turns off, that smell is blown out.

I know proper sealing via foil tape or otherwise can sometimes be missing but was wondering if anyone else has noticed this on their ride?