Two air conditioner pumps off a single through hull and strainer.

[GreenWave]

Originally Posted by OS2Dude

You could also share the pump if you don't want another hole. When I was thinking about adding a second A/C for our v-berth, the manufacture said it was OK to have a single pump and strainer (Again, if sized correctly for simultaneous usage) but you will have to use a set of relays so either/both A/Cs can turn the pump on. Not sure why, but have had other people confirm that.

With my shared setup my pump has a separate panel switch. Simpler but one does have to remember to turn it on regardless of which AC unit is being used.

[mvmojo]

Originally Posted by OS2Dude

You could also share the pump if you don't want another hole. When I was thinking about adding a second A/C for our v-berth, the manufacture said it was OK to have a single pump and strainer (Again, if sized correctly for simultaneous usage) but you will have to use a set of relays so either/both A/Cs can turn the pump on. Not sure why, but have had other people confirm that.

You need a relay for each unit that you want to be able to control the pump. Us an a/c relay and wire the coil (pick) to the wiring going to the air conditioner compressor. [I like solid state relays but mechanical is fine too.]
Anytime your thermostat calls for air it turns on the compressor which will also turn on your sea water cooling pump. When the compressor goes off, the relay loses power and the pump also turns off. Each unit needs to be able to individually control the pump otherwise the pump either must run continuously or it will only run when the unit it is wired to calls for it. If both units call for water simultaneously, both relays close to run the pump but that's OK since the pump is running on it's on a/c circuit and just using the relays to tell it when to run.

[Coolerking]

https://www.marine-j.com/pdf/222000650.pdf

Again....please...just read the manual.
This is not complicated.

[thinwater]

Two pumps is done all the time in chemical plants etc. That is not the problem.


You need check valves so that the one pump cannot dry the other system. Suction sounds large enough.


There could be other plumbing problems. The flooded suction and constant rise requirements are often violated. Also, no 90s within ~ 6 inches of either pump inlet (turbulence).

[Turtle Blues]

Work on a lot of boats with single pump to a chiller setup. The math to make it work is straight forward as stated above. The downside is one pump goes down so does the ac, so does the cruise.
My own setup from the department of redundancy department is 3 AC units, 3 complete piping systems, through hulls, strainers and pumps. Often strainers within 3 feet of each other have very different buildup when cleaning. One system has an issue I have the capacity to continue until serviced.
I don't share the fear of multiple through hulls, I buy the best and inspect on haul out just like everything else.

[Turtle Blues]

Sorry, Dropped a paragraph.
To answer the question you asked I would second the single pump with a relay system. Because the cooling coils and piping runs are different sizes the resistance will not be equal. To achieve branch equalization in this instance the installation of a ball valve to throttle the higher flow is easiest. You can try this setup with your existing pump to see if you get sufficient flow before stepping up in pump size. The march website for example has pump curves for comparison. The drawback to stacking units in series is the the temperature differential to the downstream unit, it will never achieve the same efficiency as the primary.