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TOPIC: Preventing AC water pump forming an air lock

Preventing AC water pump forming an air lock 16 Aug 2017 15:39 #1

  • MonteVista
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As many folks have experienced it also my AC water pump becomes air locked at times. I had changed the location of the pump when I first purchased this boat (5 years ago) and that has made the situation worse, I believe. The original location for the pump was on the starboard side forward in the engine compartment and near both the water intake as well as the ac compressor. We had to move it to the sport side in order to gain more space so we could reposition the waste tank. That means long (about 3 ft) hoses for the water in take and the output side going to/from the pump. There is nothing I can do to change this. So, this year I am inserting a T-junction at the output of the water pump. The water pressure pump is very near so I am also joining the output of the water pressure pump, through a valve, to the 3rd leg (base) of the T junction being added to the AC pump. Normally, the T will be in the pass-through mode and the valve going to the water pressure pump will be set to OFF. If there is an air lock, all I need to do will be to turn the valve ON and start my water pressure pump. That will pump water into the AC water pump and should get it going. Once the pump is primed I shall turn the valve OFF to bring the system back to its normal use. Ordinarily, such a T may be better placed on the water intake side (I think). However, since the pump's propeller wings have openings among them that allows water pumped from either side to disperse to both sides. If this easier connection does not work I may need to move the T to the input (water intake) side of the AC water pump. I shall report on the results when implementation is completed, on Friday I hope.

Stay tuned and any comments welcome.

Thanks,

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Bayliner 285 Cruiser / Mercruiser QSD 4.2L 320 HP Diesel
Live in the Bay Area, CA, USA, boat in Turkey
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Preventing AC water pump forming an air lock 16 Aug 2017 15:46 #2

  • smitty477
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Our AC raw water pump would become air locked when the boat was hauled or if we ere in extremely heavy seas (rare).
The problem was that the rise after the pump caused a small head pressure that an air locked pump would not overcome.
You could just open the bleed on the output side of the pump and then it would prime but that bleed was very awkward to get to.

We added a "T" after the pump outlet with a small hose leading off the "T" to a 1/4" ball 1/4 turn ball valve located higher in a handy place.
After that when we had an air locked pump we just turned the valve 'open' for maybe 2-5 seconds and we were all set.
It would defat the head and then the pump primed immediately.

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Northport NY

Preventing AC water pump forming an air lock 20 Aug 2017 06:11 #3

  • MonteVista
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UPDATE!

I have completed the fix to prevent the AC cooling pump becoming airlocked and stop working.The attached picture shows/explains it.

Relatively simple but effective!

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Retired, computer expert / executive
Bayliner 285 Cruiser / Mercruiser QSD 4.2L 320 HP Diesel
Live in the Bay Area, CA, USA, boat in Turkey
D-Marin @ Turgutreis in Bodrum/Turkey
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