The evaporator is not frozen. Unless it was able to thaw out over a few days. In fact, I can't imagine that it could possibly get cold enough to freeze. It was about as cool as the outside of a glass of iced tea, and produced about as much condensation (per unit of surface area).

The only filters are the ones in the return vents, and we change those regularly. At least I couldn't find any in the furnace/AC unit in the attic.

The ductwork is not exactly well sealed. It looks like there was some sort of dope used to seal the seams, but it's not doing the job, not to mention the sizable holes where the refrigerant pipes go in. But I can't imagine that that would have a huge impact.

There was an odd sound coming from the evaporator. It may well be normal, but it sounded like a leak. It was kind of halfway between a whistle and a hiss. It wasn't constant. It seemed to do it for about 30 seconds, then pause for about a minute, then repeat.

There were two refrigerant tubes running into the ductwork, one insulated and the other bare. I assume that the insulated one should be the cool one. It was moderately cool. Enough to generate some condensation inside the ductwork where it was uninsulated. Inside the unit, it split into two or three smaller tubes that fed the evaporators. On the other end of the evaporators, the return tubes were more and smaller. They were pretty cool. Where they passed out of the ductwork, they were somehow joined into a single return tube, which was sometimes room temperature, and sometimes somewhat warm.