Moldy smelling A/C

My 2012 LEAF SL gets a moldy smell every fall when I turn on the Heater. It's really coming from somewhere in the air conditioning plenum as the car typically turns on the A/C along with the heater by default, (annoying). I don't notice this strong odor in the summer while running A/C only. I have replaced the cabin air filter with a carbon activated version and the smell is diminished a bit, but still strong. Has anybody got any clues where the mold is actually located, and/or a way of removing it or neutralizing it? Thanks!

Hello,
The mold gets started on the A/C evaporator. Back in the old days (@Cadillac) we would mist Listerine into the plenum with the fan running to coat the evaporator. The smell starts up when there is condensation. Check to make sure the plenum drain functions (does water drip out with the ac on in humid climate).

Don