first: follow pahonda's post it is the least evasive, cheapest and may work to your satisfaction. since your car is garaged it probably isn't real dirty
a question :"I havent used the A/C since last fall"
does this mean fan and/or heater too?
i've driven cars with the faint smell of something not right, as long as the drain hose is not plugged (water flowing freely under car on a humid day) I just turn it on high and let the condensation flush old water out.
of course it depends on your sensitivity to smells,
second: download shop manual remove blower and clean evap from blower's side,
third: since your a/c is working and you don't have the tools you don't want to go there, about $300-400 or more in tools. plus the chance of breaking little plastic parts or worse
happy 4th!

I hope that you are not advising him to leave the evap in the car,, if so ,,that is not a very good advise at all .

..if you want to clean the evap properly YOU HAVE TO REMOVE IT ,,, that is the only and proper way to clean it ,,( and not just clean it while still on the car by just removing the blower assembly ,,,,,,, and also you need to replace both insulators ..
when evap is off the car, you need to separate the 2 cases,( this will remove all the junk that might be at bottom case that plugs the drain hole ) clean the evap core, ( plug the pipes )clean the 2 cases ( soap and water,) replace insulators, spray fridgy-fresh ,, reassemble ...
Now if the core ( fins ) is badly plugs, enough to restrict air flow and you cannot clean it ,then you might have to buy a new evap core

of course to do so, you need to evac and recharge a/c system ,, but this is the only way that will last ,, unless you just by a complete evap assembly and replace it

no need to buy expensive tools, have a shop evac the a/c system , keep track of how much freon in the system , you can remove and clean the evap, when done, have the shop recharge the a/c system ,, it should only cost you around 40-50 dollars, assuming you got some hand tools and don't have to buy them

It is against the law to purposely vent refrigerant that is in a system, but people do it all the time, I have not done cleaned the evaporator yet on my car but am gonna do it soon. Any thing that has to do with a/c can be difficult and to do it u need some special tool also. When u get the eva changed out u will need to vacuum the system, to remove all the moisture and any non-condensables which is very important for the system to work properly. Not sure if ya can just gain access to the evap and clean it w/out removing it . As far as a shop doing it, it will cost a lot of money,period. Shops charge even more cuz of the laws and standards set by the E.P.A, and they wont go around the regulations.bla bla bla. Maybe you can find out if ya can clean it w/out removing it. good luck...

Make sure to replace the 2 pieces of Foam and maybe the grommets.
 

I also had a moldy smell in the AC of my 2005 honda accord.

I tried frigi-fresh several times and it helped temporarily. But I ended up having a mechanic change out the evaporator core for a new one. He showed me the old core and the metal was free of mold. It was the foam insulation around the unit that had mold on it, just like deserthonda mentioned.
Wierd mold, like hair; but black in color. Not what I want to breathe in to my lungs.

They replaced one piece of foam, but only cleaned the other one because the supplier did'nt send the correct part. They claimed to have bleached it.

But now it is back, but more faint. I could have it re-done with all new foam. But there may be another thing to watch for. After calling the Airsept people, the tech mentioned that there are rubber grommets that also have to be replaced.

I am now looking for a new car since it also has a some other problems. But I wish that some one had told me to make sure the mechanic gets all new foam insulation, both pieces, and replace any grommets that could be affected.