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Marine Air Conditioning System Maintenance
August 13, 2009
3:15 pm
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Steve Pooler
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November 12, 2008
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You may not be able to see the data plate/stickers on the air handlers...From your description it sounds like they are the old EFB model air handlers (The data sticker will be on top of the A/H) that have a propeller style fan blade mounted in a cage on the back as opposed to a squirrel cage blower that draws air thru the coil and blows thru duct...

The total BTU of the two air handlers needs to equal 16,000 BTU (17,000 total is ok but 15,000 is not ok) for that system.

Depending on years...Those air handlers came in 4,5,6,7,8,10,12 & 16,000 sizes.

The EFB air handlers did not move near as much air, and could be the reason for the higher temp differential.

Also there really was no good way to filter the return air to them because of how the fan mounted...If you have access to the back, you may want to take a good light & inspect the coil behind the fan blade to see how clogged it/they are...It's only 4 slotted screws on each to remove the fan assy, lay it over to the side and wash out the fins with some coil cleaner (try Home Depot or Lowes for the cleaner)

If you do connect your gauges I will need to know the following:

Seawater temp.

Cabin temp.

Both Low & High pressures...All at the time you take the readings...

Also from your description of "feel" and the fact that the system will heat...It sounds like it's full of R-22.

Steve~

August 13, 2009
2:02 pm
carver3007
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Steve, it is a split air handler system, I have one evaporator located forward in a cabinet with two supply grills and a 12 x 12 return with filter,,,I am the 4th owner of the boat and yes when I pulled the filter after taking possession of the boat, it looked like a lint/dust rug,,,could not believe how bad that thing was. One vent supplies the vee berth and the other blows into the Galley and main salon area. The return pulls from the vee berth.

The other evaporator is located in a cabinet in the aft cabin and it too has two vents one blowing into the aft cabin and the other blowing into the main salon. The return is same size as the one indicated above and pulls from the aft cabin its filter was in bad condition first time I changed it. There isn't any flexiduct in the system the air blows directly thru the coil and out the supply grills. At this time, I don't know the btu ratings on the evaparators,,,,next time I go to the boat I will inspect the coils and see if I can find a rating plate on each.

The set up, as far as I can tell is factory,,,the boat is 1982 vintage. I am not sure if the compressor/condenser unit is original. I think some of the old papers that I have indicates that the compressor/condenser unit had a major overhaul around 1996.

If I set it on heat,,,,it does supply heat.

I am using a March LC 3CP MD water pump and I just replaced the old one with a new one that I had as a spare, The old one would start and stop on me,,,,I chased out the water supply from the thru hull intake to the  discharge and took the inlet filter and totally cleaned it but the old one was unreliable. Haven't had time to take the nose cone off and inspect.

The compressor housing is warm to the touch,,,,not enough to pull your hand away but it is warm.

Next time I go down to the boat, I wll take my gages and some freon 22 and check the operating pressures both high and low. I will make a trip to Sears for the wrench.

thanks Steve, I wil report my findings,,,might be a couple of weeks before I can get back to the boat.

August 13, 2009
11:17 am
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Steve Pooler
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Also...As far as getting the valve/s open....You really need to get a refrigeration service rachet....You can find them at Sears or many other tool supply houses...

Steve~

August 13, 2009
11:10 am
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Steve Pooler
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Hi again Terry,

Just to get others up to speed...Terry asked his question in an e-mail to me...I had asked that he post further questions here for others benefit...Which he is now doing...Thanks Terry...The next post is a copy of my e-mail answer to him...

We continue....

Terry...A Beer Can cold suction line is good....As long as it's not frosting, or the compressor is not sweating & Beer Can cold too...The compressor should be room temp to slightly warm...

The 20 degree differential you mention is not so good, and indicates an air flow restriction thru that air handler...Not enough air flowing across the evaporator coil...15 to 18 degrees is what we are looking for and a 20 degree exchange means the coil is not picking up enough heat...

Things to look for are clogged return filter/s...Some installations have 2...One in the return air grill, and another on the coil fins...This one was shipped installed on the coil when the unit was new...Most folks never now it's there, and I have pulled some out that look like a piece of dirty shag carpet...

Next is duct size & condition...I would need to know the size of the air handler ( you have two on one compressor ?) or did I misunderstand ?

If it's only one air handler...A 16,000 requires 7' duct and around 80 sq inches of total discharge grill area...

Return Air...A 16,000 needs around 120 to 140 square inches (12X12" grill is good) and the path for that much air to flow to the coil.

Leaks in the discharge duct that might recirculate cold air into the return can be another reason...

Both High & Low side pressure reading would help...But the above are the things you can check easily...

Steve~

August 13, 2009
10:28 am
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Steve Pooler
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Hi Terry,

When running is the suction line (low side) beer can cold & sweating, frosty, or warm ?

Reason I ask is...You may have trouble with that valve and twist the stem top right off...Also never use vise grips, or channel locks...They just bugger it up.

Yes there are a few tricks to open it that I will explain, but there are also a few reasons to not get into the system...

First is the valve and the obvious problem that may result from forcing it...
Second is the possibility of inducing air or moisture into the system if you are not familiar with how to do it properly...

You can run the system in heat mode, and that will heat up that valve so that it might break loose but be sure to shut the unit back off before trying to open it.
In the heat mode that valve is now the high side and you will ruin your low side gauge with the normal High side pressure that should be present...

Another trick is while attempting to turn the valve with steady clockwise pressure....Take a hammer and smack down directly on top of the stem (and wrench)

If the unit will not heat but runs in heat mode...It's likely low on freon...If it won't run in heat I can tell you how to make it do so, but that will require moving a wire temporarily...

Let me know what the suction line feels like, and the high side pressure is just as important as checking the low side alone if you are going to go ahead...

Most times getting to know what your unit should feel like at a few key spots is better than opening her up to contamination...

Steve~

August 13, 2009
10:08 am
carver3007
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Steve, I was wanting to put my gages on my older 16,000btu 110v split Crusair unit on my boat just to see where the high and low side pressures were operating. I could not get the back-seat valve to open on the low/suction side, I was using a box end wrench as that is all that I had that would fit the stem. I was attempting to open by turning the stem CCW but read on the Dometic site that I should have been turning the stem CW. Anyway I did not apply much pressure on the wrench as I did not want to break anything. Just wondering if there are some tricks of the trade to get a stubborn valve to open. I know the first rule is to turn the stem in the correct direction,,,at least now I know.

My suction line is beer-can cold and sweating,,,,not icey at the compressor and my thermometer at aft supply grill was reading 60 Deg with temp inside the cabin around 80 Deg. On a 95 Deg day on the Florida panhandle in an old 30ft aft cabin style not sure it would get any better than 80 Deg inside.

March 23, 2009
8:38 am
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Steve Pooler
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** you don't have permission to see this link **
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

** you don't have permission to see this link **

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~