86 Mariner 3697 AC water pump

[MrMojoRisin]

New owner here... boat was already out of the water by the time we completed the purchase. Seller told me the AC water pump was bad and needed replaced. I want to pull the pump out to confirm it is defective. So couple of questions. What is the best way to test the pump now that we're in winter storage?

Also, how do i confirm that this pump is the original pump that came on the boat? Reson for the qustion is a buddy of mine has a 34' Silverton with a single AC unit and the pump he just replaced on his was 500gph. The one in my boat currently is only 300gph and, if i'm not mistaken, is supplying water to two AC units.

I'll try to attach a picture of my existing pump.

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Is that enough volume for two AC units?


Boat is approx 2 hours from home, in storage, but they are winterizing tomorrow so i'm going up this weekend to grab the batteries and take some additional pics and measurements. White there I was going to pull the pump and check the strainer while i'm at it.

[g36]

If that is a 300 gph pump then no imo its not enough for 2 ac units. I couldn't find info if that exact P300 model so if it's truly a 300 gallon pump it would really be not recommended for anything but a very small ac if any because you also gave to figure how much lift it has to overcome and all the bends etc that will affect and reduce total water flow. I still have one marine air systems unit in service. I reviewed my marine air vector manual it didn't really mention a particular size but Rule of thumb: marine ac Systems require approximately 1.5 GPM per 12,000 BTU (1 ton) of cooling capacity. Taking it out and testing it at home won't do a lot other than telling you it's moving water. I really would look into sizing a new pump for your 2 new ac units. My 405 has a 2 ac units on one MARCH PUMP, AC-5C-MD 1020 GPH pump and it does fine so imo at least sizing up from your 300 gph is necessary.

[waybomb]

Sounds a if the po installed a smaller pump based on the above calcs. But a word of caution - double check wire sizes and the relay box to make sure it's all sized for the new bigger pump.

[waybomb]

I believe the main cabin is a 16000 btu and the one under the bed is 9000. 25000 btu/24000 btu x 1.5 x 60=187.5 gph. So 300 gpm should be correct.

[MrMojoRisin]

That's what i was wondering when I saw a 300gph pump... Of course, without being able to find any specs on the existing pump, I was just assuming that the "300" on the pump was the gph. I'm not sure if that is the original pump in there or not, but it doesn't appear to be newer, at least it doesn't jump out at you that it's obviously not 40 years old.

I only see one breaker for the A/C water pump, but do have 2 breakers for A/C units. So i'm assuming one pump feeds both. Since i'm going to be there anyway this weekend, i may just try to pull the pump to take home and see if it works at all. This might be a project better pushed off till the boat is in the water and i can go through a full startup to troubleshoot. But if i take the pump off now, and it doesn't work at all, i can go ahead and get the replacement ordered.

Source of the post I believe the main cabin is a 16000 btu and the one under the bed is 9000. 25000 btu/24000 btu x 1.5 x 60=187.5 gph. So 300 gpm should be correct.

MarinAire makes a 500 gph and a 600gph in the same size pump housing/configuration. It has a 3/4" inlet vs a 1/2" on the 300. I'll check this weekend if the inlet on my existing pump has a 3/4" inlet. Too hard to tell from my pics. Would it be harmful to the system if i were to upgrade the pump to the 500gph as long as my circuitry can handle the requirements?>

Thanks again for the input.

[km1125]

In a northern climate you'd be OK with 300GPH in that situation. If you were down south with a lot warmer water temps then having more GPH would be advisable.

Disassemble the impeller section of the pump. There could just be debris in there preventing the impeller from turning. They are frequently just magnetically-coupled to the motor, so it doesn't take a lot to stop it from turning.

Any larger pump would be fine, but if you go too big you're just going to be restricting the flow anyways with the smaller hose sizes.

[waybomb]

The ac pump switching is in a box in the cabinet under the galley sink on the aft wall of that cabinet. A joy to get to.
When either ac unit is on, the pump is switched on with the relays in that box.
Easiest way to get to it is pull the door off the cabinet and lay down on the floor. In fact, the only way. Unless you had the sink out like I did. I also installed a larger sink so I had a bigger sink hole!
You don't need a bigger pump.
You can buy just a new head if the magnetic part is shot.