AC not priming

A

ALKA2710

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Mar 5, 2007
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25407
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New problem just started. AC works fine at the dock but when I take the boat for a ride and anchor and turn the generator on the AC pump looses its prime. I have to take the hose off the pump after the impeller. Once I hook it back up the pump works fine. Than I get back to the dock and no water pumping. I have to stick the dock water hose in the outlet and it primes and than works fine at the dock for days as long as I don't go for a ride. Anyone have any ideas. Only thing I can think of is pump is shot or air is getting in the system at the pump.

Al
 
The pump has to be flooded (full of water to work) it is mounted too high, or the hose that feeds it goes too high. The hose and the pump has to be below the water line of the boat.
 
My only problem is system is on a 2002 boat and never had this problem before. Can I just lower the pump a few inches and see if that solves the problem.
Al
 
Yes but the hose from the thru hull can't be above it either.
 
If the pump was mounted too high, why did it take 13 years for the problem to surface?
 
Originally posted by Gregory S

If the pump was mounted too high, why did it take 13 years for the problem to surface?
[are you sure you don't have an air leak at the strainer or something stuck in the water intake?
Click to expand...
 
Yes check strainer. Hose could have moved up a bit.
Keep in mind that the pump has no suction
 
What's kind of pump is it? On March pump I have seen one or more of the plastic vanes crack. Easy to check as you can just pump the screws on the cover and check the impeller. They re available from March,

Now the question is what has changed to cause this to surface after so long? If thre was an air leak under suction at the strainer or a hose, you d see a drip when the pump is off.

I would check two things... First, make sure the intake hose between the TH, strainer and pump is clear. You could have dead shells or debris trap in there causing all kind of issues. Second, when is the last time the coils have been flushed? Again loose debris in there may cause all kind of issue including preventing priming.

That's on reason why I am not crazy about using a hose to back flush and prime with pressure... You can easily dislodge debris, push them back further in only to have them move back downstream but not necessarily getting out. Here in Florida we ve been having more and more little mussel like shells growing in AC systems. They're about 1/4" but I ve seen manifold completely filled and clogged up with them.
 
Will check all the hoses today. As said something changed as boat is older. Also have to check and see what model pump it is I don't know off hand. Thanks for all the advice.
Al
 
If ...it has a rubber-impeller type pump , slightly scored blade tips or pump housing wear-surfaces can prevent initial prime when the blades contact the surface. In that case the dock-hose priming would bypass normal initial suction-prime and allow the pump to work in centrifugal mode to keep water moving.

But, as the above replies suggest, any upstream restriction would require more initial suction , possibly more than the small pump can normally provide.

Suction air leak may be another possibility but less likely since it works Ok when dock primed.
 
A short term fix...close your thru hull each time you go out in the boat.
I have to do it on my boat, but it has been like that ever since we installed the AC unit.
 
Al,
Eel grass is really bad this year. I lost flow on generator and my engines and ac are picking it up too.
My theory is you have a few strands of eel grass that is caught in the tube from bottom of boat to strainer.
They probably relax and spread when at dock and when underway they flap and block the hole.
I would do this Clean and remove strainer. With strainer out, open seacock. If water gushes, great, if not then I have the adapters, you can put them on, hook up a hose and let water run out the seacock at the bottom, that should clear them.
If water does gush when opening, they may flow thru with basket out.
 
Thanks again everyone. Went and played around with the AC pump today. Could not find a name on the pump so would assume it is an original pump. Took out the strainer and was clean. Opened up the seacock to strainer and had water coming in so put that all back together and tightened up. Took the hose off after the pump and put a fitting on it and flushed the system with high pressure from garden hose. I also took the 90 degree fitting off of pump and had water flowing out of pump but only after I took the fitting off, no water coming out with fitting on. Put everything back together and AC was working at the dock. Too windy to go for a ride so will have to wait and see. Will also try and back wash thru strainer this week.
Al
 
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