Well, the A/C thing went rather well, if $500US is rather well.
The issue was traced back to two small leaks in two lines. The repair guy (same guy they always send, he's a champ) was able to patch those, then recharge the completely depleted refrigerant.
Had that not worked, then it would have been replacing the whole system, around $12-$15K.
I love the repair guy. In the 16 years he's been coming here, I think he may have spoken 30 words at most. He's almost emotionless, but I think he's just a no-nonsense guy.
He almost made a joke today. He pointed out the two leaks and said:
"Two ways to go on this. Braze these. Some risk. If I do it wrong, it can get in the line. Plug it. New system."
"What's the other way?"
"Forget that. Get a new system."
So I asked him to try fixing it, and he exhaled meaningfully, said ok, then added:
"Don't worry. Been doing this 35 years."
And that was that. Fixed it up a treat. House is ice cold now.