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Troubleshooting AC pump - won't start after clogged sea strainer

Discussion in 'HVAC' started by incoming, Jul 27, 2022.

  1. incoming

    incoming Member

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    I have a 230V Marathon pump feeding 5 AC units. The AC pump is not "on demand" - it is powered up seperately from the main panel, and runs continuously unless manually turned off, regardless if any of the AC units are turned on.

    I recently moved the boat to FL (had been keeping it on the chesapeake bay). After beeing away from the boat for 2 weeks, I started the pump and noticed water was not flowing. I checked the sea strainer and it was badly clogged with growth - very difficult to remove stuff, like weeds clinging to the strainer bowl.

    I got it cleaned out, added some chlorine tablets to the basket, powered on the pump and it still doesn't start. I can't detect any sort of humming or vibrating or any indication that it is running when powered on.

    I attempting to re-prime the system by
    1) removing the bleed screw from the top of the pump - water streams out. Pump seems to be below the water line.
    2) there is a t on the outlet where the water is diverted to a bank of 4 A/Cs on one side of the boat and another AC on the other side of the boat. I couldn't figure out a way to prime both sides at once without installing a new T and garden hose adapter, so I removed the raw water inlet hose from the AC on one side of the boat (we are above the water line at this point). I put a garden hose to it, in my mind forcing any air back through the line, through the T at the outlet of the pump, and through the line that feeds the other bank of A/C's. This should leave water in the system all the way up to the inlet of the AC's units on both sides, but not all the way through the heat exchangers to the raw water outlets on each side of the hull. I thought this would be sufficient to prime everything; perhaps not.

    I turned the power on to the pump, and it still won't turn on. I verified power at the panel/breaker; i have not checked the power on the pump side because i have no reason to suspect a power problem given the sequence of events above.

    Is the pump not starting symptomatic of a priming issue, a suction issue (e.g., not enough flow through the strainer to the pump), either, or neither?

    To prime the system, do i need to get water all the way through to the AC outlets above the water line on the boat hull, or is it sufficient to just everything filled with water from the through hull inlet through the pump and up to the AC raw water inlets?

    Is it worth dissassembling the wet end to check the impeller? I'd assume if the impeller was bad, the motor would still turn, it just wouldn't pump anything.
  2. motoryachtlover

    motoryachtlover Senior Member

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    My experience with a similiar set up is that the pump will prime by removing the bleed screw. My pump is turned on by demand from atleast one unit. Beyond this I can’t help.
    incoming likes this.
  3. incoming

    incoming Member

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    Ok interesting. Seems like the pump has always powered up as soon as i flipped the breaker. But perhaps i've usually turned on at least one unit at the same time. Now that i've re-primed it, i'll try turning on one of the units at the same time as the pump and see if there is some sort of relay that starts the pump when at least one of the AC's are on.
  4. motoryachtlover

    motoryachtlover Senior Member

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    Yes I would give that a try. I have a separate breaker for the pump with an LED light. I turn the pump on first and then flip breakers for each AC unit I want to run. I have the SMX 2 controls and it is not at all uncommon for a unit to turn on by just turning the breaker on. Not requiring me to ask for cool on the control panel.
  5. dewald

    dewald Member

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    Welcome to boating in Florida. If your sea strainer was that badly clogged, then your intake and out flow hoses are probably clogged also.
  6. incoming

    incoming Member

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    Never had this problem with my previous boat, stored at the same marina I’m at now, but that was only a few months and largely in the winter.

    does it tend to be worse when using it more often and sucking stuff in or when sitting for a week or two and not running?
  7. Pascal

    Pascal Senior Member

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    First of all, if the pump doesn’t start as in the motor doesn’t turn then it is not a priming issue. Don’t waste time trying to prime it.

    you need to know whether or not the pump runs at all time or whether it runs only when a compressor starts. First you said it was always on as long as the pump breaker is on then you said you re not sure

    trace the power from the pump back and see if it goes into a relay box aka triacs. If so, then one of the unit needs to be in cooling mode for the pump to run

    If you don’t see any relay box and the power comes straight from the breaker then check for power at the pump but it’s likely a problem with the pump.

    strainer cleaning frequency depends on location in Florida. Some places are worst than others, sometimes it varies from one end of a pier to the other. Personally I m a big fan of external South Bay strainer. No more clogged strainer, you just need to make sure your diver scrubs them every month.

    in SoFl and maybe elsewhere we re having an issue with small white mussel shells, about 1/3” that growths inside hoses and coils. They get loose and clog manifold and fittings. That’s a frequent cause of issues.
    captholli likes this.
  8. incoming

    incoming Member

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    i'm definately going to verify the starting process for the pump. I really seem to remember the pump coming on immediately as soon as I flip the breaker switch in the past, and staying on even when all A/C units are off. But now I'm second guessing myself. It would be awfully nice if this was the problem.

    In terms of growth - is it common to get growth on the impeller, locking up the pump and motor? Does dissassembling the wet side of the pump need to start becoming part of my maintenance routine? (sounds like a pain)
  9. Pascal

    Pascal Senior Member

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    No you shouldn’t have to disassemble the pump head to clean it.
  10. Capt J

    Capt J Senior Member

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    I have seen this needed on Magnetic drive pumps. But not on shaft driven pumps.
  11. incoming

    incoming Member

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    i was able to get the pump running again this weekend. it did not come on at first, even with the salon AC on, but after i turned on a couple of the AC units, it kicked on, then turned off again when the AC units tripped off due to insufficient flow ("HI PS"). I started everything up again after a few minutes, it sputtered a little, then started running smoothly and didn't give me any more problems. Seems like maybe it just takes a minute to get going after its lost prime, and sometimes the AC units shut off due to a low flow fault before the pump can get going.
  12. Pascal

    Pascal Senior Member

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    You could have a bad trigger on the salon AC which would explain why it only started when you turned on another unit

    the pump shouldn’t loose prime unless you open the strainer.
  13. motoryachtlover

    motoryachtlover Senior Member

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    I have had the exact situation that Pascal is referring to. Becomes more difficult to troubleshoot when you have multiple units running off 1 pump at the same time. Then the unit with the bad trigger will be very intermittent as the other 2 units are demanding water at the same time that the unit with the bad trigger needs water thus masking the fault.
  14. Pascal

    Pascal Senior Member

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    I have never understood why AC manufacturers don’t put a **** override switch on their relay boxes so you can just start the pump to troubleshoot it without having to trigger HPFs… duh!
  15. Capt J

    Capt J Senior Member

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    You can test the triggers with a multimeter.
  16. Pascal

    Pascal Senior Member

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    Of course but I was talking about troubleshooting the pump. Priming issue, flow issue etc
  17. Capt J

    Capt J Senior Member

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    Yeah, if the pump is 2 years old or more, it's most likely the pump. I generally only get 2-3 years out of any sea water pump unless it's a march with a magnetic end.