So Sportsmbile designed or owned the rights to the Starcool air conditioning system. To my knowledge, Danhard provided all the parts for the system. The starcool system is integrated with factory air conditioning system. The factory system will not run without the starcool turned on (blower switch). When the engine is running the 120 volt compressor will not be turned on, the freon will be directed through both system.
When not running, you will need shore power, this is where the thermostat comes into play, it is not used when the engine is running. The system will not use parts of the factory system when running on shore power. I can't remember the actual numbers, but when never perform as good as the system when the engine is running.
My manuals link has the combine operating and maintenance manual for Starcool III, as also inserted a picture of the fluid levels that was on my van. As others have said, if they just fill to the manf standards it will not be full. I just would give the manual to the mech working on the van. It is important, while testing for them to turn on the unit when testing. You can't really leave it on as the fan will always run.
My experience was the system was like an icebox when driving, performance while driving not nearly as good. It is important to note that while plugged in the unit still uses a good amount of 12 volt power, so you will need to have enough to power both your charger and the Starcool compressor for long runs. The other thing to note is while the compressor will cycle on and of with the thermostat, the blowers will not.
I believe around ( 2008 maybe) Sportsmobile came out with a replacement they called the Danhard System. This system would operate independently of the factory AC. It was a more efficient compressor that could be used with a 2000 watt inverter. I never owned one, so don't know much about it other than that. I have provided a Danhard manual in the manuals link also. There was some discrepancy over the rights to the Danhard system. I was at one time looking at converting from Startcool to Danhard. When I originally talked to Danhard, sounded like it was very possible. I put it on the back burner for a year, and when I reconnected I was met with some pushback, they said Sportsmobile owned the rights, when I talked to Sporsmobile they said Danhard did. I finally got Sportsmobile to provide a letter to Danhard that I could purchase one. Between the cost, and they also wanted me to be a licenesed HVAC installer I did not go forward.
As far as parts for Startcool, when I went to Danhard for a Rotolok valve, they didn't have one (found on Ebay), so there is no guarantee they have parts for Starcool.
The pictures you show are kind of where they attach the rear system. The manuals show the hose paths and flow for both operational modes. I suspect there would not be an off the shelve hose for the rear system, and you need a custom hose made.
Also, on the manual link you will a Starcool flow diagram. I provided this to aid in going through the relay panel and following the different operational modes.
I hope this helps.