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Old 05-08-2016, 07:39 PM   #1
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Air Conditioners/Pump

I searched to see if this has been posted before without any luck.

I have four AC units on a split system. Meaning I have two PMA1000C raw water pumps, each feeding two A/C units.

The two A/C units on the port side are running fine, pumping good water and cooling nicely.

The two on the starboard side are not. When I hit the switch the pump does come on for between 5 and 10 seconds, but no water out the through hull. The A/C unit comes on but it also switches off. After about a minute they both try and cycle again, but again switch off.

I tried both A/C units on that side independently, same result.

I do not think it is the units themselves since it would be a coincidence to have an issue at exactly the same time on both. And the pump is running. So to my mind it can only be two things. A blockage in the RW supply. The through hull is open and the strainer is clear. Or there is an impeller in the RW pump that has gone bad.

Anyone know if these pumps have impellers?
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Old 05-08-2016, 07:46 PM   #2
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I would guess the impeller may be bad. The motor is probably permenant magnet and impeller may be slipping. Easy to check. I replaced mine since I am replacing my ac units.
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Old 05-08-2016, 07:51 PM   #3
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Depends on the pump. Some have magnetic impeller other a rubber one . Type?
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Old 05-08-2016, 07:57 PM   #4
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PMA1000C

A quick google shows "Magnetic-drive impeller means no seal to wear, leak, or repair."
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Old 05-08-2016, 08:12 PM   #5
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Start looking for blockages.
The PMA1000 is a relabeled March AC-5C-MD. The impellers rarely go bad but it's easy enough to open the pump and see what's going on.
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Old 05-08-2016, 08:13 PM   #6
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Take the hose off the outlet of the pump. You may or may not have the solution shortly. Closing the seacock before you remove the hose might not be a bad idea. After removing the hose, open the seacock to see if you have flow. If there is flow, close the seacock and energize the pump (it will be a small mess).
If the pump splashes water, there likely is a blockage after the pump.
If no splash, probably the pump.
If no water comes out when you open the seacock, there may be a blockage before the pump or the boat isn't low enough in the water.

These pumps are generally centrifugal and many are magnetically driven. Centrifugal means they must be below water level to prime. Magnetically driven means that some thing can block the impeller from turning even though the motor is running.

If water comes out with the seacock open but the pump doesn't make it splash, turn the pump off and try to spin the impeller by sticking a screwdriver in the outlet and flicking the impeller to turn it.

If you find that the blockage is after the pump, check the discharge outlets. Mud wasps love to use them to build homes.

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Old 05-08-2016, 08:34 PM   #7
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Thanks OC.

I read that his can also be caused by an air lock - especially if the boat was out of the water for a while. She was on the hard for about 3 three week in March.

We will see.
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Old 05-08-2016, 08:49 PM   #8
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Quote:
Originally Posted by menzies View Post
Thanks OC.

I read that his can also be caused by an air lock - especially if the boat was out of the water for a while. She was on the hard for about 3 three week in March.

We will see.
I had a vessel that suffered from AC pump air lock all the time when out of the water. New vessel learning curve maybe.
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Old 05-08-2016, 08:54 PM   #9
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The impeller in a March pump can go bod. So don't rule that out.

Loosen the outlet hose from the pump and make sure water squirts out to proof that the pump is primed and that there is good water flow to the pump.

Then to run a unit agsin. If there is still no flow you most likely have a pump issue. Try running it again while you can listen closely to the pump. If it only hums with out making a spinning sound the impeller is most likely hung up.
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Old 05-08-2016, 11:31 PM   #10
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If the March mag drive pump runs without prime for a while, it will melt bushings inside the pump head. Been there, done that. Check for prime, if that is ok and still no pumping, take head apart and look at the bits.
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Old 05-09-2016, 04:44 AM   #11
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pumps

Quote:
Originally Posted by menzies View Post
I searched to see if this has been posted before without any luck.

I have four AC units on a split system. Meaning I have two PMA1000C raw water pumps, each feeding two A/C units.

The two A/C units on the port side are running fine, pumping good water and cooling nicely.

The two on the starboard side are not. When I hit the switch the pump does come on for between 5 and 10 seconds, but no water out the through hull. The A/C unit comes on but it also switches off. After about a minute they both try and cycle again, but again switch off.

I tried both A/C units on that side independently, same result.

I do not think it is the units themselves since it would be a coincidence to have an issue at exactly the same time on both. And the pump is running. So to my mind it can only be two things. A blockage in the RW supply. The through hull is open and the strainer is clear. Or there is an impeller in the RW pump that has gone bad.

Anyone know if these pumps have impellers?
They should have impellers in them typical. Also you might want to check if they lost their prime. I had one do that on me. When I prime it again it worked fine.
Good luck
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Old 05-09-2016, 05:27 AM   #12
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Greetings,
Mr. IR. Welcome aboard.
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Old 05-09-2016, 07:51 PM   #13
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Well, after lengthy research here and on Google, I read a few times to try giving the plastic wet end where the impeller is a sharp smack as sometime sand and grit can jam it up. So I went down there with a small rubber mallet and gave it a smack or three.

Well lookie here - turned on the cabin A/cs and water came out the arse of the boat and she started cooling. Still running two hours later.

We will see if it keeps up!
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Old 05-09-2016, 08:21 PM   #14
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On my 16k cruisair heat pump, I use an 800 gph Attwood baitwell 12vdc pump.
I switch it on with a relay, so when heat pump calls for the motor to run, it just turns on the relay which turns on the pump. That pump is cheap, quiet and reliable.

http://www.amazon.com/attwood-Attwoo.../dp/B0036GNYVC
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