Priming my March pump and AC

[grnoles2]

Hi, I thought I would try this. Every time I leave the slip ie I unplug from the shore and shutting off the AC, my AC/pump loses the prime and I have to go the the aft birth dig through the floor reaching my pump and re prime it when I get to a dock or go on my gen set.

Any ideas. March pump says that he problem is not their pump.

It is a new unit since Jan 2022 when I bought this 2011 Catalina 355. Lol AC worked then, but it was January and I didn’t really use it after I left the sales dock. Ever since it’s been a problem.

Any help or suggestions are welcome

[capt jgw]

Probably the location of the intake through hull and the shape of the hull are causing the water to be sucked out and replaced with air. Not much you can do about the location but a scoop shaped through hull or through hull screen, facing forward, might tend to force water in rather than sucking it out.

[misssherry]

I close the air conditioner raw water seacock when I am going sailing. This prevents air from getting to the March pump when the boat is heeled and banging into waves.

[Wolfe10]

Originally Posted by misssherry

I close the air conditioner raw water seacock when I am going sailing. This prevents air from getting to the March pump when the boat is heeled and banging into waves.

Yup--do the same.


And, if prime is lost, open thru hull, and with a hose, reach over the side of the boat and force water into the outlet. It will backfill the system and prime the water pump.

[grnoles2]

That’s a new idea. It’s a long reach but may be better than destroying my aft bunk area every time I move. Thanks I’ll try this. Actually both. I tried the sea cock once and it did not work. Thanks. Though. I’ll try again. I also added new hosing so maybe that will help.

[cr180]

I installed a self priming air conditioning pump made by Shurflo. Solved problem.

[gonesail]

any way to position the pump a little further below waterline.

[SailingHarmonie]

If your March pump will not prime, your plumbing is not correctly designed.

All piping from the thru-hull to the pump, and from the pump on the the AC NEEDS to flow uphill. If there are ANY downhill sections, a bleed valve will be required on the pump outlet. The March pump can NEVER suck water up from the ocean if it is full of air. If the air can not flow out of the pump--on its own, you are always going to have a problem. This is (or should be!) made clear on the installation diagram for every marine AC unit.

Sounds like whoever installed your AC unit didn't know this, or didn't think it was important.

[s/v Jedi]

I have a fresh water line with valve connecting between seacock and pump. I use it to flush and to prime: close seacock, open valve, start A/C, wait until sound of air bubbles is gone, open seacock, count to 5, close valve of freshwater, done.

I use the same connection for running barnaclebuster through the system, with a piece of hose looping back from the A/C unit instead of dumping overboard.

[Spindrift NH]

A little off topic here but, Jedi are you using your ac pump to circulate the barnaclebuster? I’ve always removed that pump from the system and used a cheap(er) pump to circulate the mixture for fear of ruining my ac pump. I’d rather not go through all that hassle if it’s safe just to use my ac pump.
sorry for the thread drift

[grnoles2]

Can you advise the model number. Thanks

[grnoles2]

Thank you.

[s/v Jedi]

Originally Posted by Spindrift NH

A little off topic here but, Jedi are you using your ac pump to circulate the barnaclebuster? I’ve always removed that pump from the system and used a cheap(er) pump to circulate the mixture for fear of ruining my ac pump. I’d rather not go through all that hassle if it’s safe just to use my ac pump.
sorry for the thread drift

No, I use a small bilge pump in the bucket with solution, pushing it through the pump. I would pump it, but don’t want to run the A/C, heating up the solution

I do zip-tie a sock to the return hose to catch the shells coming out. I learned to remove it when a ball of shells has formed in there because if you don’t, it all gets dissolved, neutralizing the acid.

[CaptTom]

Back to the OP's question, in my last boat I put a "T" in the hose near the pump. I ran a hose from that vertically until it was up above the waterline, and in spot which was easy to access. On the top of that I put a ball valve.

Opening the valve released the air which had been trapped in the hose around the pump, to be replaced by water flowing in from the thru-hull. Close the valve again and the pump is primed and ready to go.

I agree that, in a perfect world, the hoses all run uphill from the thru-hull, but reality has a way of intruding in these things.

[Be Free Sailor]

I replaced a Shurflo and installed a Marchpump.
Had the same problem, - resolved it by adding a oneway/checkvalve on the pump outlet.
Works great, just needs to be primed one time at start of the season.