A/C cooling will work as long as the air is dry enough. In order to condensation occur, some conditions are required.
Firstly, I would like to clarify exactly what is condensation. Air is a mixture of many gases, mainly nitrogen and oxygen. But there are other things in too, including H2O(g). And from these three gases, H2O is the one with the lowest condensation point (I'm just simplifying things here desconsiderating other components of the air). Therefore, in contact with a sufficiently cold surface, H2O will be one of the first substances to condensate. That is exactly what condensation is: H2O(g) colded into water. Visible fog is condensation too and is simply many very little liquid water spreaded in the air. Remember: gases form an homogen mixture, thus when you put two gases together you'll not be able to distinguish them.
Besides this long explanation, it's perfectly possible to have sufficiently low condensation (I mean, lower enough so you can cool you PC with it) using A/C cooling. In fact, the humidity of the air from the A/C is quite low, because in order to cold the air a bunch of water already condensates in there. However, it's not that low so we can exclude the possibility of condensation. In places where the humidity is very high (like here in Brazil), the A/C may not extract sufficient H2O from the air, thus there's still enough water to condensate and this may lead to problems with eletronic equipment. If you see condensation occur in the plastic grid of the A/C, then you may have a big problem with your computer. A test that you could do is that one Restorer said. However, it's recommendable you do it in summer, when the humidity is higher.
Another point is that we do liberate a lot of water into the air. You can see that when is a very cold day and you see fog when you breath. Thus, whatever you do to make outside air to not come without passing though the AC, the room humidity will always be higher than the air that gets out from the conditioner. Because these equipments are configured to stop at a certain temperature, there will be inevitably room air entering into the case. You must me aware of that, too. A better test in this case would be leave the metal board getting cold air from the AC from one side, and monitor the another for about 2 or 3 hours, and trying to simulate the air flow that happens in the case. Then you'll be able to see if water condensates. If it does, no way. And one more thing: condensation is obvioulsy inevitable if the airflow is zero and the surface is colder than the air. Low temps of the surface are a necessary condition - not a suficient one.
I hope that this post clarifies things to you.
Firer
