Marine Air Conditioning System Maintenance
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Greetings All, 
Let’s start with the basics…
Seawater flow thru your A/C system is primary…
Without water flow….You have NO cooling !
Service people on the docks (at least the better ones) can walk down the dock during the summer and tell which boats they are likely to be getting a call from next just by the flow of water (or lack of) going overboard on each boat….Lack of seawater flow can cause other problems besides loss of cooling…
- Lack of seawater flow causes high system operating pressures
- This, in turn increases the amperage draw from the A/C unit
- Possibly leading to: Burnt up wiring at switches or shore cord ends
Many of these symptoms can stem back to the cause of low water flow. If the flow is allowed to remain restricted, compressor failure can also occur in some older systems.
Different than land based systems, Marine systems installed below decks have no fan to remove the heat from the refrigerant…They use water to carry away the heat for many reasons…
- Water is more efficient than air as a heat exchange medium
- Size of a unit with air cooling is much larger, thus making air cooling impractical on boats
- Air cooled units require a exit path for the heat so that the space they are in does not continue to heat up as they run, thus reducing their efficiency further
As you see from the picture above….It’s an example of a seawater strainer to a system that has seen little love, and this system of course did not cool.
Every boat owner should become familiar with their boats overboard flow rate when the system is clean, and become accustomed to glancing at it every chance they get…Once you have established what is normal for your boat, a simple glance may be enough to recognize a mounting problem, and thus head off a ruined trip due to the loss of A/C…
The first question a tech may/should ask when he gets a call Is…”How is the seawater flow ?”
More frequently than not…The owners answer is he thinks it ok, or Yes it’s flowing…Only for us to arrive to find not much more than a trickle….All this is ok for us as techs…but if you would like to save that expensive service call…Keeping your strainer from looking like the picture is a great start !
Seawater strainer maintenance is not hard to do…But of course every boat or installation is different. You should also know that the more the system/s run…The more frequently you will need to clean the strainer. During the winter months here in central Florida we find that due to cooler water (marine organisms seem to grow more slowly in cooler water) and obviously less usage you may not need to clean the strainer but once a month….Summer is a different story !
Depending on where your boat is moored, Tidal flow, Water Temp, and Running the system/s 24/7 can require cleaning the strainer as often as every week…I have even seen worst case situations where a boat may be moored in a pass with much tidal flow (and grass flats nearby) causing the grass to “Tumble” in the water down to where the thru hull is located, thus requiring the strainer basket to be emptied in a matter of hours…
Steve~
About the Author: Steve Pooler is a marine air conditioning specialist based on the West Coast of Florida. His marine repair background started in the 1970's at a family owned and operated boat yard in St Petersburg, Florida. Steve has a knowledge of most all specialties involved with marine and yacht repair. For the last 20 years (11 of which were for a Cruisair distributor) Steve's specialty has been yacht & boat air conditioning and refrigeration service.
Greg | Jan 21, 2009 | Reply
Steve, What a great and informative web site for marine AC. Having worked on several boats with you in the past I think its great that you share your experience and knowlege with folks looking for a little guidance.
Keep The Air Flowing Cold.
Gregory K. Davis
Bill | Jan 29, 2009 | Reply
Hi Steve, love your web site – lots of great info. ! Our company does a lot of yacht maintenance / mechanical preventive maintenance type stuff here in Wilmington, N.C. – my question is, do you have an opinion concerning back flushing the sea water lines on marine air conditioning systems ? That is, do you think there is any benefit to occasionally (2 or 3 times per season), removing the water discharge hose and connecting a dockside water hose to the unit and pumping water backwards through the system. I have talked with some individuals who believe that doing so helps to remove/reduce the amount of marine growth in the coils and hoses, eliminating the need for or reducing the frequency of acid cleaning. Any advice or opinions you can offer would be greatly appreciated.
Steve Pooler | Jan 29, 2009 | Reply
Thanks for the favorable comments…They are appreciated…
As far as back flushing with fresh water is concerned…I can’t say much about marine growth in your area…
But if you were speaking about this locale…I’d say pretty much all they are doing is wasting fresh water…
Shutting a system off for a few days will starve the organisms of oxygen and stop/slow growth…(It’s why they don’t show up in engine cooling systems, or seawater supplied heads)
But some folks are either not willing, or can’t to do that…They either want it cool when they arrive, Live aboard…Or they have water cooled refrigeration that has it’s seawater supply tied into the A/C pump as well…
A running system however will not allow growth in the condenser coil itself…It’s too hot in that section of the flow path…
That’s not to say…That the condenser will not accumulate hard water scale acting as an insulating blanket preventing efficient heat transfer (like a dirty radiator in your car)
Down here we tie growth to…Pump flow rate & Run time…The two seem to walk hand in hand…
The slower the flow rate is…Allows them to attach easiest. (Faster boats that are underway most of the time, seem to get less bottom growth too)
The longer the pump runs…Just gives them a more constant flow of oxygen, and the fresh food to get bigger, thus slowing the flow more, which eventually chokes off enough flow that the unit will not run…One Compounds Another…
The newer digital controls seem to have helped for single A/C system boats because the pump only runs with the compressor when the T-Stat is calling for cooling…Thus less pump run time.
Older 3 knob controls ran the pump on the fan circuit and thus anytime the fan was running…So was the pump…You can change this by wiring the pump to the compressor circuit (after the T-Stat)
However on boats with multiple systems on one pump…
The pump runs pretty much all the time because one of the units is likely calling at any given time (If they leave more than one system running, or have water cooled refrigeration)
Some folks say when I tell them all this…OK…I’ll just run One system while I’m away…Thing about that is…One system may not be enough to satisfy the T-Stat in the summer, and thus more pump run time…
My Opinion ?…Best thing to do is either shut everything off while gone…Or to setup & utilize the Humidity program of today’s digital controls to reduce run time while away….
We do have customers adding Bromine tablets to the sea strainer basket with some success, and there is also a product out called Bio-Guard that is nothing more than a copper tube inside of a clear PVC tube with threaded PVC couplings that you can install in-line…
As the copper deteriorates, it releases into the water stream copper oxide (active ingredient in most bottom paints)
I have installed a few…End of summer should let us know how well they work.
Again Thanks for Your Interest…I hope I helped some…
Steve~
Taylor | Apr 6, 2009 | Reply
Is there a way to become a content writer for the site?
Steve Pooler | Apr 6, 2009 | Reply
Sure Taylor….and Thanks for your inquiry…
You could register to the forum section…Just click on Forum at the top left of any page…
It should then give you a link to register…Free…Then you can comment or start any topic you choose to write about…
I look forward to reading and interacting with you, plus all others…
Steve~
jsaunders | Jun 14, 2009 | Reply
Steve,
Can you simply put a piece of copper tubing in the sea strainer?
Steve Pooler | Jun 14, 2009 | Reply
Sure…And I have been doing that with reported good results…Usually I cut two or three pieces depending on the size of the strainer & and basket.
Some have asked about using pennies…Not the same though since a penny nowadays is mostly zinc with a copper coating…
Steve~
jsaunders | Jun 20, 2009 | Reply
Steve,
Thanks for the info. I will give that a try and report back in a few months. Just to let you know I base my boat in the upper end of Tampa Bay in Dana Shores. The water gets very warm and has poor movement in the summer months so this should be a great testing ground for the copper tubing to show its stuff.
John
Steve Pooler | Jun 22, 2009 | Reply
Ahh Dana Shores…Many Moons Ago…I once knew a girl who lived…Those waters are Hot !…A bit dirty & fun too (I seem to remember more movement though)…Well never mind……
Anyway I’m familiar with those waters, and grew up on Tampa Bay (Upper & Lower) in my boats as a young man…
Please do keep us up to date on how the copper tubing reacts in your system’s sea strainer…
Oh…and if you run into…Well like I said…Never mind….
Steve~