Try pouring some watered down lysol(or something along those lines) into the fresh air intake right in front of the windsheild while you have the a/c,fan or watever you choose. it should kill some of the musty and mold in there.
Or indirectly spray some air sanitizer stuff below the dash where the recirculating air intake is, while you have the blower on recirculate.
To prevent the mold/musty smell, i try to turn off my a/c, defrost,fan about 5 mins before i get home, so that it has enough time to clear the moisture out of the system. B/c the mositure staying inthere is causing the bad smell