Navigational (global Positioning System) Gps problems of the 2004 Infiniti G35

While driving, ac came on full blast and I could not control it. None of the buttons worked on the unit at all. I have read similar complaints and their fix is the controller board or aftermarket radio system. I have an aftermarket radio/gps unit installed, but it still have zero control over ac unit. No problem with radio ever. All of this is intermitteningly. Sometimes I can control it, but it want last long. Don't know what will happen this winter, since I have only owned the car for 5 months. I'll keep researching.