I'm starting to get the old musty smell from the A/C unit.

I usually run the A/C system in Auto mode and change my cabin air filter each year. I don't seem to have the same problem with my TSX?

Has anyone tried the A/C flush stuff for the coils or any other remedies to kill the smell?

Does the smell change for better when the car is washed?

The reason I ask is because the air is drawn in just behind the hood. Sometimes after a storm I pick up the same smell. Try recirc mode for a while, does it go away? If not it may be in the vent plumbing.

and make sure there is not any debris inside that vent. sometimes you can get a bunch of leaves built up in there

I had a pair of panties up my vent.

The musty smell is not consistent. It seems it happens more on more humid days (humid days are rare in NM). I can check my vents and A/C drain hole.

I've seen in the past those A/C foam sprays to remove coil mold/mildew buildup from the condensation from humidity. I wasn't sure if it was worth doing or if there was a better fix.

Nah, save your money, sounds like musty water in the intake breather (not the engine) for the interior; that is nestled in behind the hood adjesent to the windsheild. Take some water and soap to that area. see if the smell dissappears. The water should not pool up, and should drain out, stop if it pools up!

At gas stations, that window cleaner that everyone uses while pumping gas, sometimes kids (retarded grownups) do some crazy things with that water. I make it a habit not to use those. Because any of that water seeps into the breather you get skunky air for a while. Station attendents usually do the minimal amount of work to get by, and neglect those, in some places(not all). In my case a simple car wash fixed it.

Good luck

Try one of the anti static sheets that you put in the clothes drier! Cut it in strips and stick a few in the cabin air filter>>>>should give a nice smell

^
that will just mix the musty smell with the fabric softner smell... it won't get rid of it.

True

I've been told that it can be caused by humidity being trapped in the condenser(?). It was recommended to turn the A/C off for the last couple of minutes of driving to pass fresh air through the ventilation system before turning the vehicle off. Hope this helps.