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Old 06-05-2013, 11:20 AM   #21
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...Why 2 pumps? Is air conditioning a critical system? Why add complexity and cost?
We have 2 - 16,000 BTU systems with 1 pump. After talking to AC repair guys they suggested 1 pump for simplicity. If 1, 2 or both units are on, the pump is also. We split the water to each unit after the pump.

If you are going to use the AC while under way, you should also have a sea water scoop. AC pumps are not self priming and the scoop will help keep water to the pump (s) while traveling.
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Old 06-05-2013, 11:57 AM   #22
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>>>A sweaty grumpy wife may be a relationship hazard <<<

You haven't met this sweaty grumpy wife. Actually we only use the A/C in a marina. We only ran it a couple of times while cruising to cool the boat down in the evening at anchor and a few times in the morning to get the chill off while coming down the East Coast in October.

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Old 06-05-2013, 03:32 PM   #23
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Depends upon that sweaty grumpy wife's ability to curtail the use of the boat, could be a risk of selling said boat..
Geez! Don't let your wives have that much power! My wife does exactly what I say and always walks a little behind me. (Is she reading this?)
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Old 06-05-2013, 04:01 PM   #24
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Geez! Don't let your wives have that much power! My wife does exactly what I say and always walks a little behind me. (Is she reading this?)
ROFLOL!!

You da man Walt!!!

Do me a favor and train mine for me, 26 years of trying has gotten me nowhere compared to you
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Old 06-05-2013, 04:06 PM   #25
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My wife walks behind me as well. Does it count if she's always yelling at me to slow down?
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Old 06-05-2013, 08:43 PM   #26
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Not all "sweaty grumpy wives" are bad.

My “sweaty grumpy wife” gets up in the middle of the night, goes up to the main cabin, lifts the port engine room hatch ( it’s got gas hyd lifts so it’s pretty easy), shuts the seacock, removes the strainer basket, and dumps the debris and jellyfish over the side.

Puts it back together and restarts the AC unit and crawls back into bed without once waking me.

I’m a lucky guy.

As an aside, did you know you can have too much water flow thru a AC condenser? I learned the hard way.

Mike
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Old 06-06-2013, 06:54 AM   #27
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Sceptic , did you use a choker collar with spikes , or the electric unit with a remote to do the training?

Any boat or RV work , by bride sez" BLUE WORK," and its not her problem.
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Old 06-06-2013, 03:10 PM   #28
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>>>As an aside, did you know you can have too much water flow thru a AC condenser? I learned the hard way.<<<

OK, I'll bite, tell us about it.

Bob
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Old 06-06-2013, 03:15 PM   #29
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As an aside, did you know you can have too much water flow thru a AC condenser? I learned the hard way.
Doing a $60K+ repair on a boat right now for just that reason.
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Old 06-06-2013, 08:33 PM   #30
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I’m hoping RickB will return and correct this post, subtract from it or add to it as necessary.

During the rebuild of the little DeFever I installed a 16,000 btu Aqua Air ac. I wired it up electrically, installed the electronic controls, the seacock and strainer, ducts and return grill, and then stopped working on the ac. The boat was on the hard and would not splash for at least another year.

I put the boat on a truck to go back to SC to have the Cummins installed.

I asked the yard to complete the plumbing of the ac.

2.5 years later the Aqua Air failed. I called a repairman. His conclusion was that I had water in the refrigerant.

So I started looking for a replacement. I noticed that Mermaid published min. and max flow rates for their units. I had not seen max flow rates on any other site, so I called Mermaid tech support and was given this answer - “too much water results in turbulence and if there is any grit in the water it’s like a little sand blaster. It takes a while but you end up with little holes.”

Next I called Aqua Air and got the exact same answer.

I went down into the engine room and looked at the pump name plate for the first time - 1000 gal per hour - double the recommended upper limit by both suppliers.

Like I said, I learned the hard way.

Mike
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Old 06-06-2013, 10:19 PM   #31
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I'm glad that our Mermaid A/C unit now resides in the dumpster at the marina. I've never had a unit that gave so much trouble. But I guess 1000gph is a lot of water. I didn't realize they made pumps with that capacity.

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Old 06-06-2013, 10:55 PM   #32
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A March AC-5C-MD is a common pump to use in marine air conditioning systems.
It moves close to 1000 GPH and will handle close to 50,000 BTU.

The March LC-3CP-MD would be appropriate for a 16000 BTU system. It can handle up to about 25000 BTU systems. It moves close to 500 GPH.

On my little 5000 BTU unit I use a March LC-2CP-MD. It pumps less than 300 GPH.
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Old 06-07-2013, 07:40 AM   #33
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“too much water results in turbulence and if there is any grit in the water it’s like a little sand blaster. It takes a while but you end up with little holes.”
That's it. There doesn't have to be any grit, the high velocity will erode the tubing walls all by itself. If there is any contamination like a tiny barnacle sticking to the side of the tube it will create a cavitation bubble behind it that will fairly quickly bore a hole in the tubing wall and put seawater in the refrigerant that will instantly destroy the compressor.

That is the problem we are dealing with now, the builder installed a single pump large enough to supply 3 large chilled water units and the resulting high velocity eroded the tube sheets on all 3 condensers in just a few months and destroyed the compressor on one. We are going back with 3 properly sized pumps and a head pressure controlled VFD drive for each.
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Old 06-07-2013, 07:58 AM   #34
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500 GPH is what all the documentation (pump and A/C Mfg'rs) recommend for a 15K-16K BTU reverse-cycle unit. I didn't notice the max flow rate, but it makes sense now. Anyway, I already bought the two pumps, one for each, not knowing where I'd end up putting everything.

For me it makes sense to have two separate systems. For now I have to feed them from the same through-hull. There is another unused through-hull in a convenient location for the forward unit, but it needs to be replaced. Next time the boat is out of the water, that will be one of my first jobs. Don't get me started about the idiot PO who used a ball valve from a home improvement store and an uncoated pine fairing block.
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Old 06-07-2013, 09:03 AM   #35
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I have five A/Cs that run off a single pump. Works much better then those cheap plastic A/C pumps they try to sell you for big$.
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Old 06-08-2013, 06:54 AM   #36
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NICE , centrifugal , no rubber vanes to wear out.
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Old 06-08-2013, 10:22 AM   #37
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All the A/C pumps I've ever seen have been centrifugal pumps, that's why they require a flooded inlet.

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Old 06-11-2013, 09:36 AM   #38
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Status update:

So far so good. The two pumps run fine together or separately. Initially at least, no air is back-flowing from the "off" loop through to the running loop. The A/C units work great in both heat and A/C mode. Next project, hook up the ducts and registers.
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