I feel your pain! Sorry, but it's such a great ( bs ) line. But seriously, I have an "84 760 GLE w/ acc and I live in Montana. Beleve me when I say that I know what a pain the acc system is. Try making through 20 degree winters w/ that system working properly! As for fixing the ac in your ride know this:
1) If it's been open as you say,then the entire system ( hoses, condensor, etc ) are contaminated and as such will give you problems and may result in poor performance and/or failure.
2) Once a system is unused, especially in a dry area as yours, nearly every seal in the system is subject to failure becuase the lubricant is no longer present to keep them in proper condition. Hence, putting a new compressor may only be the first chapter in your education about ac ( ie, when the system is charged, it leaks everywhere and your now faced w/ an entire rebuild-you don't want to know about that! ).
I don't know how much you love your brick, but for the potential cost involved, you might want to consider a different brick.