A/C freshwater pump prime problem

[Jim Wharton]

I'm having problems getting my freshwater pump to stay primed aftersailing. When I'm at the dock the pump seems to stay primed, but if Itake it out for a sail almost every time I have problems getting thepump to prime. In the install manual it did note this could be aproblem. However, being an engineer I got to figure out why and fix it..We installed a 12K reverse cycle unit in a 1991 Hunter 30 (under frontVberth). The boat had a 1.5in seacock at the aft end of the boat (headdischarge not being used) which is about 2ft aft and to port 1.5ft theprop shaft log (as close to bottom of the boat as you can get). Wereduced the output to the seacock from 1.5in to .75in and installed astrainer. From the strainer we ran a short hose red striped to the pumpprovide in the kit. All the equipment to this point is below the waterline. From the pump output we ran hose to the A/C unit under frontVberth approx. 25ft. Then setup the water discharge approx. 7in abovethe water line.Once the pump is primed at dock the unit can be turned off and on andworks fine (even leaving the boat idle for a week (use boat onweekends). However, every time we take the boat out, we have to turn theunit on and off several times to get the pump to prime. Looking at thehoses at the pump there is air in the line (not a lot). I'm trying todetermine if the line is getting a suction (back flow) on the line, orair is being brought in due to the prop, or what?I'm open to any ideas you guys might have.Thanks Jim jim.wharton@fnc.fujitsu.com

 

[Clyde Lichtenwalner]

Suction

My guess is that the long line to the AC unit is just below the waterline. The boat's motion (wavew action, heeling, and forward) reduces the static pressure in the line allowing the system to drain slightly and introduces air to the pump from the water discharge. There is only only one easy solution. Close the seacock before you go leave the dock. This is not a bad idea anyway. It eliminates one place where you can take on water due to leaky hose fittings or failed AC components. It is always good practice to have unused seacocks closed.

 

[Bryce Grefe]

pump prime

I had a similiar problem with my fridge pump. Installed a back flow preventer between the strainer and the sea cock. haven't had any problems since then. But it is always a good idea to close the seacock.BryceS/V Spellbinder

 

[Bill Bell]

Close Thru Hull

I have the same problem with my A/C if I don't close the Thru Hull. I only have 4 ft of hose between the thru hull and the pump, but I lose prime when sailing with the thru hull open.Bill

 

[Bill Ihlenfeldt]

AC prime

I had a similar problem on my 410. You need to make sure that the intake is below the waterline and that everything flows "uphill" from there to the pump. The dealer had installed mine and there was a short section where the water line dipped a bit (It was hard to find). Once I eliminated that dip, the problem was solved. I never close the seacock and have sailed in all kinds of weather at many angles of heel.Your owners manual emphasizes this and even shows some diagrams (Marine Air).