If you have mold that has grown on the evaporator fins inside the cabin, there's no need to take apart the whole a/c unit. Rug Doctor makes a product that is called Odor Remover that they sell where they rent machines. Put it in a spray bottle and go to town. It kills mold, mildew, and works good to get rid of smells on the floormats too. I've used it and it works great.

As far as the evaporator goes, take out the glovebox, and remove the blower motor/fan and its casing. It'll take about 30-45 minutes to do. With the blower motor out, saturate the area with the RD Odor Remover. Let it sit about 15 minutes, and spray it out with clean water from another spray bottle. It should drain out the normal a/c drain (assuming that its not blocked with mold). If the smell persists after the clean water spray, wait an hour for it to dry and respray with the Odor Remover and rinse again.

Take the car out for a drive after reassembly without running the a/c, but with the blower motor on high.

Don't use bleach, as it could ruin whatever carpeting it drips on and it isnt too good for plastic either. The Odor Remover doesn't smell too bad either.