Of all places you should be able to find an outfit in Phoenix that specializes in AC.
But welcome to the converted camper van world. It get's tricky with all the aftermarket stuff.
Find a reputable shop and give them the contact info for Danhard. They have service reps that can help. When mine went kaput I found a whole slew of other issues but if all you need is a basic service it's really just about topping off the refrigerant and making sure there are no leaks. And this might sound like a stupid question but you do know how to operate it? When they modify the lines there is now refridgerant running through both the OEM front as well as the Starcool on the rear so both need to be on at the same time. If you have a thermostat in the rear that actually does nothing unless you are plugged into shore power.
If the pull anything apart make sure they check for metal shavings or other debris in the orifices. That would indicate that your compressor has failed or is on it's way to doing so. An orifice takes the place of an expansion valve and controls or regulates the flow of refrigerant and there should be one at both the compressor and the Starcool side of things. There might be some useful information in this thread: http://www.sportsmobileforum.com/for...tion-7835.html