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Old 23-09-2011, 21:43   #1
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Low Water Flow on A/C Discharge

I'm looking for advice again.

Just today I noticed the water flow has diminished on the water discharge of my air conditioner. It's a reverse cycle system about 12,000 BTU. There are no error codes and the unit is still functioning as usual.

It was installed by Anchor Marine in Tampa years ago, but they were bought out or otherwise out of business.

Weeks ago I read all the documents on board concerning the unit to learn what I could about how it works in preparation for any needed maintenance or repairs. And it seems that time is soon upon me.

The flow path is ..... thru-hull/seacock -> Groco 750 strainer -> March Pump LC-3CP-MD(mag drive) -> AC unit in/out -> above waterline discharge.

Haven't pulled the strainer out yet, but it appears to be fine looking through the clear housing. The top is stuck hard or I'd have it out right now. I can get it out, but just took one shot at it so far.

So, there is a restriction somewhere or the pump output is low. Possible restriction points could be the thru-hull/seacock, intake hose, strainer, input hose, AC unit, output hose, or discharge thru-hull.

I plan to check the intake thru-hull of course, but the boat is docked on a lay wall and I'm always concerned about getting in the water between anything and the boat. I guess I'll have to do it or move the boat to anchor. Not a problem as I have sailed daily or weekly for a more than a year now.

Also, I could to do a half-split check by disconnecting the pump output and turning it on to observe the output. If normal looking, I'll disconnect at the unit itself to observe the flow there. Maybe there is a kink along the hose path to the unit that is getting clogged. It runs from the starboard side main cabin thru the head into the vberth and across to the port side vberth storage area. The longest hose in the system.

I suppose then I'll check at the output of the unit as well. And finally the output hose to the hull will be checked. Somewhere along the way something has to be the issue.

I'm still at the physical inspection stage, but if that doesn't reveal anything I'll proceed in some manner.

So, if you're still reading, here's the questions.

Does this make sense so far?

Would I damage anything if I back flushed the entire system by putting water under pressure into the discharge opening? Specifically the unit itself. And/or maybe the water pump should be out of the loop/bi-passed for any back flushing.

Do you have any advice not related to these questions?

I think a recall one of the four fault/shutdown modes is low water flow, but I need to check that again. It hasn't presented an error code yet. And I've turned the system off pended further head scratching. I don't want to damage the system.

Thanks for your time and feedback.
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Old 23-09-2011, 23:00   #2
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Re: Low Water Flow on AC Discharge

Sounds like you've got a plan. I'd start with opening the strainer as that is the most likely place to get a blockage and it is the easiest to check. It can be hard to see crap in the basket from outside the bowl. Next pull the dischage hose off the March pump and determine if the restriction is before or after the pump. You know what to do from there. I'm not sure that back flushing is a good idea but I can't give you a good reason not to. I guess you could have a bad pump, but those March pumps are pretty reliable. They do fail eventually. Otherwise I wouldn't sell so many!
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Old 23-09-2011, 23:37   #3
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Re: Low Water Flow on AC Discharge

Thanks HopCar.

I didn't realize which way the water flowed through the strainer. I considered it went from the outside into the center, via the strainer holes.

Since it moves from the inside to the outside of the strainer surface, and considering a fine/thin layer of matter on the glass surfase is partially blocking my view into the housing, I may have misinterpreted what I was seeing. I believe the holes could be visible even with considerable amounts of crap blocking them from the inside.

This will be my first time cleaning a strainer, so I'm learning here. I'm betting that's the problem, I have neglected to clean it so far.

Thanks.


BTW, I always check the prices of any parts when I start a new repair. In five minutes of searching on the Groco 750 strainer, your price was the best out of four sources I checked. By as much as $78 in one case.
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Old 24-09-2011, 00:31   #4
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Re: Low Water Flow on AC Discharge

Because we have been in marinas with some of the worst water around the world, I have had this problem a few times. Every single time it has been some sort of obstruction before the pump. The obstructions included: plastic, Styrofoam, slime, muck, green lip muscles, barnacles, and mud or thick water (India). I have been in situations that required cleaning the strainer 3-4 times a week. Obviously places that are filthy like India are problematic, and areas in warm climates will have much more sea life that will cause you problems.

One of the "special tools" that I use is a piece of PVC with a brush attached to the business end. It is sized to go through the through-hull from the inside of the boat. I have been in places where I simply could not live without this "tool." Another "special tool" is a 1 meter long piece of rigging wire that has a swag about 1" from the business end and the wires are spread open at the business end. Connected to an electric drill, this tool has worked for me from heads to through-hulls.

Hope this helps.

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Old 24-09-2011, 05:49   #5
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Re: Low Water Flow on AC Discharge

Backflushing the A/C cooling water system is not a problem at all. I do it on a regular basis, both to prime the system, and to blow out any growth in the lines.
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Old 24-09-2011, 06:42   #6
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Re: Low Water Flow on AC Discharge

Thanks for the advice, svBeBe and captain465. very good info.

I'm going to service the strainer this morning and I'm becoming more sure that is the issue. I was misled by being able to see the holes in the strainer and not realizing the debris is on the inside of the basket. If I had known this I would have checked that out before posting this thread. But I'm not afraid to reveal my inexperience to learn something new.

I'll be servicing the engine sea water strainer as well. The Groco manuals state to clean the strainers "frequently", and I have been neglectful of this.

I have found a new home port and I'm temporarily on the lay wall. The wake boards trap floating debris beside my boat on the AC intake side. I'm exposed to the ICW and east winds as well, so at times I'm pitching and rolling in this debris. I'm thinking there is more stuff entering the thru-hull than in the past.

Hoping to have the cool air flowing before the day heats up.

It's so "way cool" and "awesome" to get feedback from next door and half way around the world when I'm faced with new issues on the boat. Thanks.
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Old 24-09-2011, 06:53   #7
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Re: Low Water Flow on AC Discharge

If the system has been running for years without cleaning, it will serve you well to do it now. You might try cleaning the strainer, then close the intake thru-hull. Drain all water out of the intake line. With a small funnel at the highest point, pour in some CLR and let it set for several hours. Then start up the system and let it run. You should see all kinds of stuff come out the discharge. You will be good to go for some time. Chuck
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Old 24-09-2011, 06:56   #8
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Re: Low Water Flow on AC Discharge

You need a spanner wrench to remove the top of the Groco strainer. They're cheap. Checking the strainer is normally simple.
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Old 24-09-2011, 07:10   #9
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Re: Low Water Flow on AC Discharge

I have a wrench somewhere, I need to find it. This old boat was full of spares and special tools when purchased last year. But I'm not as organized as many folks.

The manual says "hand tight" is all that is needed for proper safe operation. But also says if one wishes to "snug" it down more a wrench is needed and available. Also states a non-petroleum based grease on the threads is a good idea.

I plan to try the hand tight approach at first to help facilitate routine cleaning. But I'll keep an eye out for leakage.
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Old 24-09-2011, 07:19   #10
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Re: Low Water Flow on AC Discharge

Chuck, thanks for that advice. The strainers haven't been serviced for the year and a few months I've owned the boat. Not sure about before that. I have just been keeping a good lookout on the discharges.

I also happen to have some CLR on board so I can do this as well today.

Sure makes life on board better to have this forum as a resource.

I'm loving it so much I'm considering putting that stupid "salt life" decal on the back window of my Chevy truck. And I've never done anything like that or wore t-shirts with anything written on them, ever.

Might even have to consider a forum burgee for the spreader halyard, when I have more than "grocery money" in the checking account. Things are tight right now.
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Old 24-09-2011, 07:27   #11
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Re: Low Water Flow on AC Discharge

You might find the following Thread of interest:

Growth in Saltwater A/C Cooling System

The following is something I posted on another thread that might be useful:

Quote:
We just used Rydlyme (Marine version) to clear the coils in the heat exchanger of our 16,000 BTU air conditioner. For this exercise I used a cheap (at WM $19.95 USD) submersible 360 GPH bilge pump in a bucket with a gallon of Rydlym and fresh water (50/50) that pumped the solution into the discharge side of the system and a return hose connected to the (normal) input side of the system and led back to the bucket. I circulated this for about two hours and then reconnected the normal discharge side of the system and pumped the solution through the input side to fill the dicharge line back to the transom. This sat over night before we pumped fresh water through the systerm for some while and then reconnected the raw water. Afterward the difference in the flow rate through the A/C was quite noticable and our "Condensator", which had earlier quite working, resumed operation with a vengence (no-zero-nada condensate making its way to the bilge).

The RydLyme certainly seems to live up to its advertising although the material is not inexpensive--in our case $39.00 a gallon.

FWIW...
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Old 24-09-2011, 11:55   #12
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Re: Low Water Flow on AC Discharge

That's a good read svHyLyte, thanks.


I have succeeded in restoring flow, the cool air is blowing.

It was full of debris, including a small crab. After cleaning the strainer however, flow rate was only marginally better. Maybe only subjectively better in fact. Next, I back flushed the intake hose and thru-hull, with no noticeable change, at first.

I was watching the discharge, feeling unsuccessful, when suddenly it spat out some blockage from further downstream in the path. In hindsight I suspect the pressure in the system was increased after cleaning the strainer and that allowed the downstream restriction to be forced out after a few minutes of running.

It's now shooting out like never before since I bought the boat, and I'm feeling relief. I was concerned about not having heat when the weather cools off soon unless I spent money I don't have on something.

I'm still going to do a CLR or other treatment sometime soon, just for good measure.

Here's a pic of the strainer. It will be good for a laugh at least.

The engine strainer came off by hand and had very little debris in the basket.

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Old 24-09-2011, 12:38   #13
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Re: Low Water Flow on AC Discharge

Nicely done! I think I'll go down to my boat and check the strainers. Do as I say not as I do! I'm supposed to know better than let them go this long.
We've got good prices on the replacement baskets when you need it. Yours looks ok for now.
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Old 24-09-2011, 15:55   #14
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Re: Low Water Flow on AC Discharge

Nice full basket, in fact I have never seen one so full and overloaded. Your instincts were right on when you started at the sea strainer. One test I do is to remove the basket and then open the seacock, this allows me to check the rate of flow as it shoots out the top. Good heavy flow over the rim is what we are looking for. Back flushing the heat exchanger coils with dockside water, don't let it get to the pump, works for me.
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Old 24-09-2011, 16:53   #15
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Re: Low Water Flow on AC Discharge

Yep, I just busted out laughing when I saw what was in there.

Once HopCar clued me in on the flow direction inside the strainer I felt sure that was the problem. Apparently one can't check the strainer well without pulling the basket, regardless of the clear housing. I thought the any debris would be outside the basket, not inside.

Now that I know, mine won't look like that picture again.
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