New to chillers

What air temps are blowing from the salon system?
Lots of air blowing?
Lots of windows and sunshine?

Ensure the servo driven water valves are working at each station correctly with it's zone thermostat.
I would not call them high maintenance but they do require an eye ball a couple of times a year. They do get stuck. The leading cause of issues.
Very often if the chilled water is not treated.

If the salon unit is the top (older) system, may (MAY) have air trapped in it's coils. There should be a bleed nut on the top of the coils.
Ensure around 15PSI water charge. Crack the nut to ensure all water and no air comes out.
Recharge the chilled water and pressure back to 15PSI or what the mfg spec states after the bleed.

Cruisair systems have servo valves to send chilled water thru the air handlers. If the air out of that handler isn't cold enough and you can feel that the evaporator isn't getting cold then chances are the valve isn't opening when ordered to by the tstat.

They also have a little metal tab you can push to open it manually.

Obviously make sure both chillers are coming on. Again it depends on the system you have Cruisair has a digital control panel installed near the chillers
Which will show status and error codes.

In cooler weather you can run on one chiller but not at this time of the year although sometimes with iffy shore power at night you can run on a single chiller.

Such a better system than the splits. I installed a Flagship Marine two chiller system on my boat and love it.

Would he really need both chillers on line for non severe (hot as heck) operation?

Assuming the system was set up with both chillers in parallel serving the whole boat in mild weather you don't need both. Or at night as I mentioned. Or if you re not using all the rooms. You can turn off some air handlers or keeping them at a high setting so the cooling power goes to the salon and whatever room is being used. The flexibility and redundancy is what make chillers a great set up

OH YES.

Let get the servo valves on the air handlers checked like we said.

You don't loose everything because you have valves to isolate various circuits. And it s a lot easier to fix a failed water hose than a leaking gas line ...

Most split system share a water pump anyway... I always carry both circulation and raw water spares.

Negative Vibes, To many Negative Vibes. *

Hoses come off the other A/C systems also. Pumps go bad also.
Good boy scouts keep spares.
I would hope the taller (more exposed) air handlers are first in the loop.

* My Donald Sutherland gig for those that remember...

One of our fall / winter treats is looking up old fav movies. Yep, gona pull Kellys Heros back up this year.
Shame they dont make entertaining movies any more.

Stack of old Bogart movies planed also.

I run straight water. In places where it can freeze in winter I think they run an anti freeze mix.