Stupid A/C Chiller System Question

It would help if you would bother telling us what brand chillers you have ...

Depending on outside and water temp you may be able to get the boat cool enough with just one chiller running. In fact today with overcast skies and rain, I ve had just one chiller running on my personal boat. Now in summer with the typical sun we need both

chillers are never plumbed in series but in parallel

In the days I ran boats with multi chillers, One unit was used until it got real hot, then the second chiller was used.
I luved one boat. Dual chillers in the engine room.

One boat we serviced, had three, it never got that hot in this area but the captain stated, in the islands when nobody closed the doors behind them selves, it took that third unit.

I can not imagine you needing chillers up there. One should do.
But reverse cycle heat??? If it's not hot enough, put the second unit on line.

BTW, I'm a wimp in the cold... BBrrrrr

Parallel gives the condensing stations the same cool water flow. Yon can tear one unit down and still have another working chiller.
Both on line, cooling the same circulating coolant is just a super chill. An extra compressor load that may not be necessary.

The general rule of thumb for heat exchange in the air handlers is 20 degrees. So if your chiller water at the air handler is 52, your cabin temp is going to struggle to approach 70 degrees. The heat outside/UV will challenge that cooling effort and result in your mid 70's. If that's sufficient for your needs, so be it. If it's not, you'll need that second unit to kick in and get the water temp down to mid 40's, and you'll see the cabin temps drop another 5 degrees.

The beauty, to me, of chillers is that you can choose to be just fine on one unit and 52 degree water temps. You aren't harming anything by doing so, and temps will likely drop a bit lower as the sun goes down.

That’s why I m a big fan of chillers. You get more flexibility and redundancy.

I converted my old 53 to chillers 4 years ago and it was so worth it. I spent about $25k on the equipment, two 36 k chillers and 5 AH , and did the install myself. What a difference. I used flagship marine. All their stuff is solid, well designed using simple off the shelf parts like relays, tstats, etc. no proprietary boards. Drain pains are stainless steel with nice sloped bottoms unlike crap air painted alum flat bottoms... love it.

One thing about chillers is that it takes a little longer than splits to get things cooling as you have to get the water down to temp. Also cruisair AH have a valve which allows the chilled water to go in the air handler. These valves have a Tstat which only opens the valve when the chilled water is cold enough

On a bigger boat it can take a while to get the water cold enough in the furthest rooms

sometimes these cruisair valves can get stuck. They have an override lever that you can push and latch in to force it open.

usually if you have air in the system you will hear bubbling noise at the AH

If you're only running the one chiller, that 52 degrees basically means that your air discharge is never going to be colder than about 72 degrees, so that will require quite some time to blend the cabin air down to the mid 70's. Consider using both chillers to get the temps to a comfort range, and then shut one down. If you use two and get that water to the low 40's, the air will blend down much faster.

On the units giving you trouble, use your temp gun on the coils. Then bleed the air, if any and recheck. Then mechanically open the valve and recheck. This should help you understand what's going on with the air handler. Check all four corners and the center of each air handler with the temp gun. That will alert you to possible blockages.

You could use the boiler system to heat your chiller water if you set it up with a heat exchanger and a separate heating loop to drive the heat cycle of the exchanger. Keep your temps in the 90's on your glycol loop. It's doable, that project. Just needs some design work. My chillers run straight cool, and I have two inline heaters at about 12 Kw each in parallel. They're a permanent fixture in the glycol loop, and are powered separately. They're set to shut off when the loop reaches around 95 degrees. Again I can run one or both, either or. Radiant heat is a beautiful thing in the winter. The love electricity, but it's a comfortable outcome.

Alaska and 90 degree temps. Something just makes that sound funny to me.
I was 3 or 4 when my father passed thru some US Army camp up there. I just have pictures of all the snow.
Pop was from South Georgia and never thought snow was serious until then.
Then back to Hawaii.

I can't speak specifically for your boat of course, but in all the chiller-based systems I'm aware of that just doesn't happen.
Air volume only depends on the air handlers speed, which isn't driven by the number of compressors running.

Don't underestimate a few degrees difference in circulating water, though.
They definitely can make overall cooling more effective.

Another typical effect of running both compressors rather than just one is how fast circulating water reaches the operating temperature, which in turn means that the whole boat cools down faster.

That’s what I like about my Flagship AHs. No valve, water flows continuously, the blower turns off when set temp is reached. Simple.