Created a way to turn off the Ac compressor if the cooling water flow quits.

You have to detect the water flow, not power to the pump.
I have had times where pump runs but gets an airlock.
For my older unit, that means compressor his side pressure builds to 400 psi, then shuts down compressor, and when pressure falls back it turns on, so with no water flow causes endless cycling of compressor to overly high head pressures. This design instantly kills the compressor power, so wont be stressing it. If water flow resumes, power to compressor resumes.
I used an analog washer water level switch with 3 levels, PART# WH12X10065

Today a hot day, I got it all hooked up and working perfectly.
If water flow quits, the compressor turns off.
I have the water level switch set to high water level.

I have a little 12vdc computer fan for the water pump, I thought it might keep it cooler.
I used a wall-wart to power the fan.
Small red wire is the water pump on wire. It connects to the water level switch, wall-wart and the water pump.
Small blue wire is for the heat pump reversing valve.
Large purple wire is compressor hot
Large white wire is compressor neutral.

The water pump is actually a dishwasher drain pump.

The entire circuit is gfci-afci breaker protected.
For these setups, there is no ground wire back on the compressor, the copper tubing is the ground wire, on the evaporator there is a ground wire, as that is where the on -off and control switches are located. It is electrically grounded through the copper tubing. I used to wonder about that till I realized it.

I am not totally done with this. I want to put a plastic cup over the water switch just in case it leaks. Was very nice that contactor had extra connections for joining wires.
And nice that if you pry the metal edge, you can make the cover removeable on the electrical box.

The main compressor wires, its just a yellow ring terminal secured in with the big set screw.

what happens if the flow is stopped by a plugged exit thru hull ?(my last issue) wouldn't a paddle flow switch work ?

timb said:

what happens if the flow is stopped by a plugged exit thru hull ?(my last issue) wouldn't a paddle flow switch work ?

Click to expand...

Ok, yes, then the compressor would shut off on a high pressure overload, but honestly I have never had that happen, not yet. I have a strainer on the hull under there.

I went with something cheap and easy to get, and that water pressure switch wont impede the flow.

The only failures for me, has been occasionally cooling water flow stops. Newer systems trip off on over-pressure only once, then have to be manually reset.

I prefer to not stress the compressor at all, hence check for water pressure.

I was imagining, what if I left the boat with AC running and the water flow quits. Then endless over pressure shutdowns and restarts, cant be good for it.

I have had jelly fish and bags float by and get stuck over the water intake and who knows what else happens under the boat.

I was there cleaning up today for 5 hours running the AC, and the water never quit flowing.

Spent the day on the water running the AC, it all worked fine whole time for hours. When I pulled away from dock and boat rocked over, water flow quit and compressor instantly turned off. Once the pump does that, it has to be turned off otherwise the water never flows again, so it works as expected keeping the compressor from shutting down on overloaded high pressure.

Other nice thing, when the pump pumps water, when turned on, you hear an audible click of the contactor, which you then know water is flowing, you dont have to look.

I'm a few years away from owning a boat with an air conditioner, but given all the problems I read about with water condensed units, I wonder why more of us don't remove all that old school stuff, glass over the through hulls, and install modern split cycle units with the condenser side up somewhere with air flow? In addition to a big savings in power demand, eliminating the hassle of using lake/river/ocean water and all it contains to condense the AC sounds huge to me. What am I missing?

Size of units and location for outside unit on MANY style boats.


Can be done sure....but there are tradeoffs.


Plus, well installed and taken care of marine units aren't that much trouble.

it may also be noisier to have a large air cooled condenser fan running.
Although if well done, an air cooled condenser ought to be less trouble.
The size though, most boats would have to have a pretty large condenser and fan and space available.