I tinkered with the air conditioner a little, and managed to get the fan to come on. No compressor though.
Vic had been freaking out about the guinea pigs overheating, so Gwen and Walter came over with a block of ice and a fan to cool the guinea pig room. Apparently Tilly and I can just suck it up.
I took the capacitors out of the AC, and went to ye olde capacitor shoppe. The guy there tested both capacitors, and we saw the big (compressor) one wasn't working, while the little (fan) one was OK, as I'd thought. I put the new big one, and the old little one back in, and the air conditioner came on eventually, and cooled the house down.