Sounds like the classic leaky evaporator and yes thats probably why the previous owner sold the car. The replacement is about $1200 and involves taking out the dash. Not a job for a rookie, if you get and inde to do it make sure his done a few before. You might want to try the Walmart leak metal/rubber leak kit, R-134 refill and pressure gauge first and see how it goes. You can fill these up yourself pretty easily (check this board for details, it talks about A/C all the time). It's a lot cheaper than the repair.