I keep losing prime on air conditioner sea water pump?

[Bob Quinn]

Just wondering if anyone has any ideas on this.

It seems that often if I go out for a cruise, I then have lost prime on the air conditioner sea water pump.

I usually don't run the air when under way.

Any thoughts on why this would keep hapening?

 

[Pascal]

What kind if thru hull covers do you have? For air con, you really want some form of scoop, either slots or better South Bay strainers.

That said, a properly installed pump should re prime easily. Two key factors: make sure it s installed below water line and make sure there are no high points in the feed hose between the strainer and the pump inlet. Sometimes going over a stringer and back down is enough to cause an airlock.

I ve had a similar issue with a watermaker feed pump, basically same as an air con pump, after running on plane. Installed a South Bay strainer at the last haul out and problem solved

One last thing, if your pump has a bronze head and impeller (oberdorfer or Scott) the impeller and head could be eroded. It will work ok when primed but be too eroded to re prime. I m done with these type of pumps.

 

[Bob Quinn]

What kind if thru hull covers do you have? For air con, you really want some form of scoop, either slots or better South Bay strainers.

That said, a properly installed pump should re prime easily. Two key factors: make sure it s installed below water line and make sure there are no high points in the feed hose between the strainer and the pump inlet. Sometimes going over a stringer and back down is enough to cause an airlock.

I ve had a similar issue with a watermaker feed pump, basically same as an air con pump, after running on plane. Installed a South Bay strainer at the last haul out and problem solved

One last thing, if your pump has a bronze head and impeller (oberdorfer or Scott) the impeller and head could be eroded. It will work ok when primed but be too eroded to re prime. I m done with these type of pumps.

I don't know what kind of scoop I have, I will look at survey pics and see if I can figure out what I have. Thank you

 

[Hat43c1981]

On our previous boat I had the same issue. I ended up closing off the seawater gate valve before we would take the boat out for a cruise which kept the water in the lines and would allow the system to hold prime. If your gate valve is easily accessed, this could be an easy fix for you.

 

[Pascal]

I can’t imagine having to shut down the air con underway…

 

[SKYCHENEY]

My 53 does the same thing. I have the OEM scoop but its right behind the stabilizer fin so I think it gets air from time to time. It always reprimes on its own but it might be a minute or two of weak flow before it picks up. So I only run the little 6K unit in the side stateroom until it primes.

I have changed pumps. Pulled the Oberdorfer and installed a March. I have replumbed the hose from the strainer to the pump to try to eliminate any high spot. Nothing has worked but I can deal with it.

After the repower, I added a pump for cooling water for the stabilizers as they were previously cooled off of the engine raw water. That pump would lose prime too. The through-hull was in exactly the same spot as the A/C pump intake but on the other side of the boat. So I had to move that one lower down below the generator to insure good flow and no loss of prime.

 

[Pascal]

Interesting. Originally the AC pick up on my 53 was aft of the ER, inboard of the shaft. I never had an issue with the Vospers disrupting flow but … well they never worked

During the repower we moved it forward of the engine as I movers the pump forward.

Yesterday on the 116 I run, the march pump that is used to cool the hydraulics when the zero speeds are used off one of the gen PTO had lost prime. No idea why. It is somewhat behind the stbd fin… I forgot about it when we hauled out in October and didn’t put a South Bay strainer like we did on the air con and watermakers. The air con was fine but for some reason the watermakers (they share a TH) were loosing prime after running on plane. Not anymore after replacing the slotted cover with the South Bay strainer.

 

[Bob Bradley]

I used to lose prime on my AC regularly on my 43C. Re-establishing it required climbing aft and outboard of my stbd engine and pulling the output hose from the pump temporarily. Real PITA, especially offshore with a hot ER. Problem was that the pickup was too far outboard and if the boat was coming out of the water running in heavy seas, or just snap rolling on the drift, it would suck air. Rather than go through the headache of relocating the pickup, I installed a TEE on the outlet side of the pump. I ran a hose from the TEE to just inboard of the stbd engine and put a ball valve at the end of the hose. Whenever I lost prime, I'd just climb down between the engines and open the ball valve, pointing the hose toward the bilge pump compartment. Usually the reduced back pressure allowed the pump to re-establish prime. From time to time I had to actually suck on the hose to get it started. Once it was flowing, I closed the ball valve and the water would flow through the system as it should. A little clunky, but way better than relocating a through hull fitting.

 

[Bob Quinn]

Thanks for all the information. Sounds like I am not alone with this issue.
I'm pulling the boat in May to get it shined up and now I know what to start looking for!

Just curious, could it be replumbed off an engine intake or would that starve too much fresh water from an engine? Just a thought.

 

[Fanfare]

While I sometimes lost prime on my AC pump my biggest problem was the strainer clogging up with seaweed and trash. It was placed where it was too shallow, getting a lot of surface stuff. Reaching all the way across the engine room to clear the strainer got to be too much. Three years ago I revamped the system by adding two larger circulating pumps and relocating the thru hull to the front of the er, just inside the forward er door where there was already an access hatch. Putting the intake deeper has been a spectacular success. I did not have to clean the new strainer (from Groco) for three months of continuous operation this year. My best idea of the year!

 

[Pascal]

Thanks for all the information. Sounds like I am not alone with this issue.
I'm pulling the boat in May to get it shined up and now I know what to start looking for!

Just curious, could it be replumbed off an engine intake or would that starve too much fresh water from an engine? Just a thought.

It would be the other way around… the engine water pump suction would overcome the air con pump and starve it

If you re hauling next month, just add a South Bay strainer on the TH.

 

[Bob Quinn]

It would be the other way around… the engine water pump suction would overcome the air con pump and starve it

If you re hauling next month, just add a South Bay strainer on the TH.

I searched thru my survey pictures and it only had pictures of two strainers. They were both the slotted type and I think they where the engine intakes. So I think its safe to assume the ac intakes would be the same type.

Am I understanding correctly that the ones with slots are not the South Bay strainers?

 

[Pascal]

Correct. The South Bay strainers have a wedge shape and the intake is a bronze mesh.