Very tired here, so bear with me if I ramble, I should have been in bed ten hours ago...
What, specifically, is your problem... By which, and not at all in a condescending fashion, do I mean the following...
Does the fan blow, but the air is not cold?
Does the fan sometimes not blow, but starts up when you hit a pothole, get to about 45 MPH, or slam the passenger side door?
Does the fan only work on HIGH?
The reason I ask is to ascertain which scenario this might be. As I do not know, I will give you what little insight I have, as I'm nowhere near an automotive guru...
Fan blowing, but air not cold... Agree with both the previous posters... The charge might have seeped out, and/or, the damper might be sticking... I have not personally had experience with the damper sticking on my Jeep, but I have had the charge go flat... I put a can in. And another. And another... With the leak sealer... And just when I was about to give up hope, for kicks and giggles, since I had an extra twenty in my pocket, I did another one. It did the trick. Seems that the leak sealer finally set over the winter, and when I charged it again this summer, it held, and now works like the day I got it.
Fan sometimes not working... I'm dealing with this problem right now. There is a bad connection, I surmise it's dirt in the plug, where the power connection meets the fan. It's a little wire harness that goes into the fan on the passenger side firewall in the engine compartment. I cannot, for the life of me, figure out how to get it off. If I wiggle it, this is after the door-slamming fails to work, the fan comes back on, and usually works for a week or so...
Fan only works on high... This is the, and forgive me if I'm recalling the wrong term, but I believe it's the ballast resistor pack. This is the creature that makes speeds 1-3 on a 4 speed system. Basically, the power travels through silly coils of wire, depending on the speed you've selected, to resist, and slow down the current, thus slowing down the fan. Electrical resistance creates heat, heat fatigues metal, and eventually, the silly coils break, resulting in only the high speed. This is located in the ductwork behind the glovebox.
I hope that this info helps, or at least, can do no harm. Best of luck to you. My bro's down in school in Ohio... Not that that's at all relevant to the situation, but thought I'd mention, you're not a student at the UNOH, are you?