do you leave the ac on then turn off the car?! if so after a few years you can end up with a musty wet smell due to water building up in the system and reciever dryer. Most commonly what happens. They make a deorderizor for the system you can get at auto part stores. Its not super cheap but its worth it. Anyway, besides that make sure to turn off your ac and let it discharge before yuo shut your car off, that will help the system keep wetness from sitting in the lines and system.
