Wait till it smells like piss, then you'll be complaining
My 406 was pleasingly odour free in this respect but interior house keeping (hoover/dust) helps a *lot* as does regular Polen Filter changes.
Basically in cars with climate control the air conditioning is turned on/off automatically rather than being 'on' all the time.
Unfortunately when the a/c is in one of it's 'off' periods then the moisture in the heater matrix box, ducting and grilles is allowed to rise to a temperature that propagates bacterial fungi and gives this 'musty' smell

it can be gotton rid of by a proper anti-fungal treatment at an a/c specialist (who put a chemical wash across/through the evaporator) it costs about £45.00 and they will guarantee it for 12 months or so.
There is also a Wynnes treatment which is basically and open-ended deoderant canister which you 'let off' in the floor well and get the hell outta there but when I tried one it didn't really work too well.
One top tip my a/c guy told me was to run the
heating at MAX for 20 mins or so and this will kill at least 60% of the bacteria
