New user.. asking a “dumb” question.. pump cycling

Jessica Gardner

New Member
Aug 4, 2022
23
Louisville, KY
Boat Info
2000 Sea Ray 340 Sundancer
Engines
7.4 454 Mercruiser with V drives
Hello. As a new owner of a 2000 340 SD. we stayed our first night on the boat and I slept down in the lower bed under the stairs, all night long there was a loud pump or something running, it would cycle off for a short period then on again… what pump is this and is it normal? The AC was set to 68.
 
Sounds like the vacuush for your holding tank. Could also be the water pump for the air conditioner
 
Not the vacuflush. I have learned that sound. My husband also said it is the pump for the air conditioner, is it normal for it to run almost constant all night long, shutting off only a few times and for only a min or so.
Only reason it concerned me is we are also tracking down a leak in the engine compartment bilge area.
 
Mine comes on when the compressor comes on.

Yeah I saw your other thread and thought about that as well. If you were running a generator while on anchor and running the AC that could be the source. The pump probably sits directly behind your firewall but I don't know on that boat, others can chime in. Easy enough to find, when you hear it running open the engine compartment and look for the noise.

It should have its own dedicated seacock, so should both of your engines and the generator. When you're under anchor you can try closing them one by one and see if your problem goes away as well.
 
Is it a buzzing/vibrating sound or a constant hum? If it’s the buzzing sound it is your freshwater pump as those are diaphragm based and knowing the other thread and how you’re chasing the leak nearly confirms your source of water to be the freshwater system.

a common place they fail is right at the inlet to the pump, there’s a plastic saucer looking thing that holds a filter screen and they love to crack
 
Is it a buzzing/vibrating sound or a constant hum? If it’s the buzzing sound it is your freshwater pump as those are diaphragm based and knowing the other thread and how you’re chasing the leak nearly confirms your source of water to be the freshwater system.

a common place they fail is right at the inlet to the pump, there’s a plastic saucer looking thing that holds a filter screen and they love to crack

i feel like it was a humming noise very loud in that lower bed, but you could also feel a vibration as well so I could just be thinking too hard about it now. I will rule out the fresh water pump this week. Thanks for your help. I will report back just for others to reference
 
Where does your AC condensate go?

There should be a sump in the lowest part of your boat for AC and Shower drains.

Is that what you are hearing?

If that sump pump is loud it might need cleaned really good or replaced.
 
I have the same boat. The AC pump is on the other side of the wall. Fresh water pump too. My money is on the AC pump.
Thank you! So I assume if it is the AC pump running all night it is normal for it to run while the AC is running/trying to keep up with the temp it is set to.. sorry I’m not the mechanically sound one in the relationship and sometimes my husband doesn’t like to answer my “make me feel better about this questions”
 
Thank you! So I assume if it is the AC pump running all night it is normal for it to run while the AC is running/trying to keep up with the temp it is set to.. sorry I’m not the mechanically sound one in the relationship and sometimes my husband doesn’t like to answer my “make me feel better about this questions”

The A/C pump is going to cycle on and off with the A/C compressor and fan. If the A/C is running, the A/C pump is running.

If what you are hearing continued after the A/C cycled off, then it's not the A/C pump. If it's the water pump, which is located on the bulkhead between the after sitting area/bed and the engine room, you in all likelihood have a leak somewhere, which is causing the water system to lose pressure and the pump to cycle on and off. Ordinarily, the water pump should only cycle when you flush the toilet or open one of the faucets. Additionally, when the water tank is low, it will stay on because it isn't able to prime. As Bill Collector suggested, this is a pretty easy diagnosis.

Start by turning the A/C off. If no more hum or pump noise, it's the A/C. If there is the same noise, turn off the water pump on the circuit panel. If no more hum or pump noise, it's the water pump. Etc.

The two other pumps it could be is the sump, under the floor hatch next to the head. Doesn't sound like that's it, based on where you are describing the noise as coming from.

The other one is the forward bilge pump under the hatch in the middle of the aft seating area. I have the same boat (2001), and that one would go on and off due to a fault float switch.

The sump and forward bilge pumps can't be easily switched off, so you'll have to access them when you hear the noise to determine if that's it. The forward bilge pump will also light up on the engine monitor on the dash when it cycles.

Very doubtful the battery charger (i.e., the AC Converter on the breaker panel) would cause that level of noise, but again, it's easily switched off. If you switch it off and noise goes away, you found it!
 
The A/C pump is going to cycle on and off with the A/C compressor and fan. If the A/C is running, the A/C pump is running.

If what you are hearing continued after the A/C cycled off, then it's the water pump. If it's the water pump, you in all likelihood have a leak somewhere, which is causing the water system to lose pressure and the pump to cycle on and off. As Bill Collector suggested, this is a pretty easy diagnosis.

Start by turning the A/C off. If no more hum or pump noise, it's the A/C. If there is the same noise, turn off the water pump on the circuit panel. If no more hum or pump noise, it's the water pump. Etc.

The two other pumps it could be is the sump, under the floor next to the head. Doesn't sound like that's it, based on where you are describing the noise as coming from.

The other one is the forward bilge pump under the hatch in the middle of the aft seating area. I have the same boat (2001), and that one would go on and off due to a fault float switch.

The sump and forward bilge pumps can't be easily switched off, so you'll have to access them when you hear the noise to determine if that's it. The forward bilge pump will also light up on the engine monitor on the dash when it cycles.

Very doubtful the battery charger (i.e., the AC Converter on the breaker panel) would cause that level of noise, but again, it's easily switched off. If you switch it off and noise goes away, you found it!

Your comments are extremely helpful. Thank you for responding and not judging my ignorance, as I want to learn as much as I can about the boat as well
 
Your comments are extremely helpful. Thank you for responding and not judging my ignorance, as I want to learn as much as I can about the boat as well

At this point, I've been through ever square inch of my 340. Engine repower, generator rebuild, electronics redo, etc. etc. etc. etc. etc. Happy to attempt to answer any question you may have about a circa 2000 Sea Ray 340 Sundancer.
 
The A/C pump is going to cycle on and off with the A/C compressor and fan. If the A/C is running, the A/C pump is running.

If what you are hearing continued after the A/C cycled off, then it's not the A/C pump. If it's the water pump, which is located on the bulkhead between the after sitting area/bed and the engine room, you in all likelihood have a leak somewhere, which is causing the water system to lose pressure and the pump to cycle on and off. Ordinarily, the water pump should only cycle when you flush the toilet or open one of the faucets. Additionally, when the water tank is low, it will stay on because it isn't able to prime. As Bill Collector suggested, this is a pretty easy diagnosis.

Start by turning the A/C off. If no more hum or pump noise, it's the A/C. If there is the same noise, turn off the water pump on the circuit panel. If no more hum or pump noise, it's the water pump. Etc.

The two other pumps it could be is the sump, under the floor hatch next to the head. Doesn't sound like that's it, based on where you are describing the noise as coming from.

The other one is the forward bilge pump under the hatch in the middle of the aft seating area. I have the same boat (2001), and that one would go on and off due to a fault float switch.

The sump and forward bilge pumps can't be easily switched off, so you'll have to access them when you hear the noise to determine if that's it. The forward bilge pump will also light up on the engine monitor on the dash when it cycles.

Very doubtful the battery charger (i.e., the AC Converter on the breaker panel) would cause that level of noise, but again, it's easily switched off. If you switch it off and noise goes away, you found it!

Also, by "aft seating area" I'm not referring to up top in the cockpit. I'm referring to the seating area/bed in the aft, under the cockpit. There's a carpeted square hatch right in the middle of the floor with a bilge pump and float switch under it.
 
Jessica, you are in the right spot. We are CSR and we are here for each other...

I'll echo this. Just about every problem I've had, I've been able to fix myself based on prior posts on this site. It is truly an invaluable resource for Sea Ray owners.
 
Also, by "aft seating area" I'm not referring to up top in the cockpit. I'm referring to the seating area/bed in the aft, under the cockpit. There's a carpeted square hatch right in the middle of the floor with a bilge pump and float switch under it.

i have lifted this hatch before and we did see the bilge so I am aware of where you are talking.. We are anxious to get down to the boat on Friday and roll up our sleeves and start problem shooting for this as well as tracking down our slight water leak in the engine bilge area.
 
i feel like it was a humming noise very loud in that lower bed, but you could also feel a vibration as well so I could just be thinking too hard about it now. I will rule out the fresh water pump this week. Thanks for your help. I will report back just for others to reference
FWIW - I don’t even know if you have a cockpit refrigerator, but on my boat I noticed the same thing. It turned out to be the fridge compressor kicking on and off. It hums and vibrates a little.

Good luck in your investigation.
 

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