Well, my wife just called and informed me that the A/C repairman couldn’t find anything obviously wrong with our system other than the fact that it was low on refrigerant. Given the age of our house (just over five years old) and the lack of any obvious leaks, this means that we most likely have a slow leak somewhere in the system. They recharged it, added a dye to help localize the leak, and then handed over a bill for $192 for the service call, diagnosis, and recharging. All in all, it wasn’t the most satisfying experience in that our house is now nice and cool, but the underlying problem still hasn’t been addressed. Oh well, we’re at least partway to a solution in that the leak should be detectable on a future visit.