1998 BMW 328 failure

The a/c controller will just turn on and off at random intervals. There doesn't seem to be any real pattern. Sometimes it comes on for a little while when I first start the car but then goes dark. Other times it won't come on at first but will flicker in and out as I am driving around. Once it comes on, the button lights will stay on even when it shuts off, but the screen goes dark. When it comes on everything, a/c, heat, rear defogger all work fine. Sometimes cold air even comes through when it's off, but only when I'm moving. I've been told it could be that the controller unit has just gone bad and needs to be replaced, but it's also been suggested that it could be a ground wire issue. Any suggestions?