For a Carrier air conditioning convention last year, LEGO artist extraordinaire Nathan Sawaya built a functioning air conditioner out of LEGO bricks!
... when I was asked to build an air conditioner, I thought "Nathan, let's not just make a replica of an air conditioner. No, Nathan, here's a golden opportunity to make something cool. Let's make a functioning air conditioner. Now that would be cool!" Please note that by 'functioning' I just meant a spinning fan. And by 'cool' I meant someone who would not address themselves by their own name.
Working feverishly at the 2006 Carrier Convention I built a functioning replica of Carrier's newest air conditioner, complete with the compressor, valves and working fan. It took every hour of both days of the convention, but in the end I was happy with the result. And with that spinning fan, wow, what a breeze!
http://www.brickartist.com/carrier_convention.html (Nathan did it again this time for Bryant air conditioner) - via Make (who has a neat post with a run-down of all sorts of DIY air conditioners)