I just tried something and it worked, so I thought I'd share. I bought a can of coil cleaner from Home Depot (for $5) and sprayed it on the coils of the air conditioner. I had to do it three times before they looked really clean (they're deeper than they look so it helps to shine a flashlight in there). It's cool in my apartment for the first time since I moved in and I could actually see the water dripping off the coils, like it's supposed to.
Also, changing the filter every week or two will make the AC work better, last longer, and use less energy. If the filter is really dirty, it can even make the AC freeze up. (If you ever take the filter out and the coils are iced over, turn it off until the ice melts, then try running it again before you give up and call the repairman)
Anyhow, I keep seeing posts where people's air conditioner has gone out...this won't fix that, but it will make it run a bit better.
good maintence tips! Reminded me to check my filter and man was it dirty again.