The Hotel San Juan de Dios was almost perfect for me. The air conditioning worked perfectly, and the wifi was strong most of the time. Very colonial with high vaulted ceilings, and it looks like it was there when the pirates used to invade the port of Havana. Very rustic in a very good way. Convenient to everything else in Old Havana. The owner spoke excellent English and was very friendly and accommodating.
The only negative thing I experienced was the little "Igor-like" assistant, who was very rude and didn't like Americans. This little bald-headed guy kept stalking me for money which I didn't owe him (which was later rectified on his part) - but his mafia-like tactics were unnecessary). Then he kept bugging me for the room key when it was only 6:15 in the morning. And finally, when I left later that morning, I said 'adios" and he said nothing at all. Very unfriendly.
But aside from that little man, everything else was perfect - the rest of the staff, the owner, the view outside my window, everything.