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Discussion Starter · #1 ·
We have a 12000 btu Mermaid with A/C and strip heat. It has always worked fine, at least until today. It has a March Pump which is pumping very strong. The intake strainer is clean as is the air filter. The unit starts fine on heat or air setting. It will run for say 5 to 10 minutes on A/C, with the compressor putting out cold air. It then continues to run but the compressor shuts off as the switch pops out. If the switch is re engaged the compressor again will start and run for a few minutes once more. This cycle will repeat over and over again, but it will not continue to run on its own.

I have checked the condensation pan and it is working fine. There is sufficient amp power to the unit.

Any suggestions as to where to start or the probable cause?
 

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Master Mariner
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It is quite possible the inside of the water circulation lines are coated with dirt. If you are in a canal, slough or river with a muddy bottom, that is a very good possibility. If you remove the intake and exhaust lines from the thru hulls and put them in a bucket with a mild acid, like On & Off Hull and Deck cleaner (muriatic acid will also work, but that stuff is VERY DANGEROUS) you can circulate the cleaner through the lines until clean.
The other possibility is that your refrigerant has leaked out. You will need a set of gauges to check that. If that is the case, then you have a leak, which must be found and repaired before vacuuming the system and recharging. This is best done by a professional as the equipment necessary is quite expensive and rarely used by a boat owner.
 

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One of None
Hunter 34
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We need to know which is "popping" hi or low pressure. High is condenser ( heat exchgr) related: water flow as mentioned,dirty or clogged. Low, is evaporator related, but air instead of water: low volume,clogged coil, filter,bad or fan motor
 

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Yeah if it is a pressure switch that is tripping it is likely a high pressure safety . A picture of the unit and which switch is tripping would help. Feel the temperature difference between water in and water out. If the water discharge feels quite hot then you probably have insufficient water flow.
 

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Discussion Starter · #5 · (Edited)
Pictures of the small, silver, breaker type item, 2 X 2 1/2 X 1" tall are not possible without some disassembly. It is reset by feel and is well hidden, and hardly visible due to space restrictions. Will try to gain access to it today.

Flow is very strong from pump on exit. Is there some internal bypass which would allow a strong flow on exit without providing cooling to necessary parts? The pump has been the issue on two occasions in the past but at those times flow was extremely poor and pump replacement cured the problem.

Headed out to jump on this issue before heat really sets in here in South Louisiana. Dumb as dirt on A/C issues.
 

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Pictures of the small, silver, breaker type item, 2 X 2 1/2 X 1" tall are not possible without some disassembly. It is reset by feel and is well hidden, and hardly visible due to space restrictions. Will try to gain access to it today.

Flow is very strong from pump on exit. Is there some internal bypass which would allow a strong flow on exit without providing cooling to necessary parts? The pump has been the issue on two occasions in the past but at those times flow was extremely poor and pump replacement cured the problem.

Headed out to jump on this issue before heat really sets in here in South Louisiana. Dumb as dirt on A/C issues.
I have a 12K Mermaid unit as well. I sounds like the cooling water flow is good until something intermittently blocks it and trips your high pressure switch. Try using a garden hose with good pressure to blow back through the line from the strainer to the thru hull inlet to clear out any debris that may be causing intermittent blockage. I have done that after experiencing similar conditions as you have and the problem was solved.
 

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One of None
Hunter 34
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Just a few clicks lookie lookie! No mention of low pressure switch.

HP trips in Cool mode / Troubleshooting / Troubleshooting and Warranty / Home - Mermaid Manfucturing - Home of Mermaid Marine Air Conditioning & Medi-Kool Climate Controlled Drug Cabinets

High Pressure Switch Activates in COOL Mode

While your marine air conditioner is running in the COOL mode, your RESET (high pressure) switch trips off.

Only a lack of cooling water will activate the high pressure switch when the air conditioner is operated in the COOL mode. The high pressure reset switch is connected to the refrigerant line leading from the air conditioners compressor. The activation of this switch is indicative of lack of water flow. This is the ONLY thing to cause the reset button to "trip." Should this device activate, it is important to check the flow of water through the unit.

Start with the sea water pump to ensure it did not lose prime. Check for kinked water hoses or blocked lines including the sea water strainer.

Lastly, ensure the air conditioners water coil is not full of debris. Even the cleanest of strainers can still allow silt, sand, or other debris to accumulate in the air conditioners condensing coil. This will inhibit heat transfer and cause the air conditioner to lose cooling capacity and run warmer - eventually causing the pressures to exceed the high pressure reset button setting of 375psi. A fresh water coil flush may be necessary, if it is deemed necessary. Simply flush the air conditioners water coil and lines with garden hose pressure water. The pumps in the marine industry are volume pumps, not pressure pumps. The flow of water through a garden hose is substantially higher and can flush the debris that may have accumulated inside the water coil. It is recommended to do this procedure at least once or twice a year. The frequency of this will depend on the caliber of water your vessel is in.
 

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One of None
Hunter 34
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personally I like larger water cooled equipment. (geo thermal)


Never had a chance to consult or help design this type of system.


I've see a few in the city and it's a good retrofit design for old buildings.

I'm just posting this to let you all know that watercooled equipment though small is basically the same as large to gigantic equipment.
 

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Old as Dirt!
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I just went through the same BS with the identical symptoms in our 16K BTU unit. The problem was first diagnosed, over the phone, as obstructed cooling water flow, it wasn't; it was then diagnosed as low freon and a technician dispatched to replenish the freon and search for leaks, it wasn't/there were none. In the end, the issue proved to be a problem within the compressor itself, evidently caused by incompatibility between the oil used in the device when it was manufactured and the oil in the freon used to charge the system (410A was originally erroneously written as 404) which caused the oils to, in effect, coagulate, obstructing the capillaries in the device. In our case, we were fortunate in that the manufacturer acknowledged the issue even though the machine was out of warranty and replaced the compressor at no charge to us. A $600+ part not to mention the cost of labor involved in the repair.

Good Luck...
 
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One of None
Hunter 34
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I just went through the same BS with the identical symptoms in our 16K BTU unit. The problem was first diagnosed, over the phone, as obstructed cooling water flow, it wasn't; it was then diagnosed as low freon and a technician dispatched to replenish the freon and search for leaks, it wasn't/there were none. In the end, the issue proved to be a problem within the compressor itself, evidently caused by incompatibility between the oil used in the device when it was manufactured and the oil in the freon used to charge the system (404) which caused the oils to, in effect, coagulate, obstructing the capillaries in the device. In our case, we were fortunate in that the manufacturer acknowledged the issue even though the machine was out of warranty and replaced the compressor at no charge to us. A $600+ part not to mention the cost of labor involved in the repair.

Good Luck...
404A for AC? WTF? I find that mostly in ice makers
Was it an older unit?

from Mermaid; "
AS MOST OF YOU HAVE HEARD - R-22 IS BEING PHASED OUT. NO WORRIES HERE! WE HAVE THE SOLUTION! MERMAID MFG. IS NOW A "GO GREEN" COMPANY BY UTILIZING NON-OZONE DEPLETING REFRIGERANTS LIKE R410A, R407C, R134A, AND NU-22D. QUESTION? FEEL FREE TO ASK!
 

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Old as Dirt!
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404A for AC? WTF? I find that mostly in ice makers
Was it an older unit?

from Mermaid; "
AS MOST OF YOU HAVE HEARD - R-22 IS BEING PHASED OUT. NO WORRIES HERE! WE HAVE THE SOLUTION! MERMAID MFG. IS NOW A "GO GREEN" COMPANY BY UTILIZING NON-OZONE DEPLETING REFRIGERANTS LIKE R410A, R407C, R134A, AND NU-22D. QUESTION? FEEL FREE TO ASK!
Actually Denise your are correct. I had a "brain slip" and spoke in error. (Earlier this AM I was reading another article on refrigeration, however, and evidently transposed the numbers.) The freon in our AC was 410A and our unit was just over two years old and by then, out of warranty. (Error in prior post edited and noted.)

FWIW...

PS: FWIW, our prior unit lasted 16 years.
 

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One of None
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I think some mfgs had compressors with non compatible oil on shelves when they found out R22 was not to be used in new production with 410a
 

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The other problem that show up as companies transition to R410a is that it is not nearly as forgiving of poor piping practices. With the old refrigerants they could get away with brazing pipes without running a nitrogen purge. Having nitrogen or some other inert gas flowing through the pipe as you braze prevents oxidation from forming on the inside walls of the pipe. R410a happens to be an extremely good solvent, and where R22 just leaves the deposits on the pipe walls, 410 cleans it right off and sends it down stream to collect in and plug up filter-driers, capillary tubes and tx valves. That certainly would cause head pressure issues! Technicians and assemblers have had to tighten up their habits and follow recommended piping practices much more carefully.

Denise, one of the buildings I look after is a residential tower with 160 tons of geothermal heat pumps providing heating and cooling to the building! We are seeing more and more interesting geothermal applications around here!
 

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Discussion Starter · #14 · (Edited)
Today was a pretty good day, hot in the boat but apparently productive. Went in the water and cleaned the A/C inlet, which was not too bad. It is one of those with slots, not just a hole so it took some time. Removed the hose on the seacock for the intake, opened the seacock and ran water into a container. Very little trash and a strong flow of clear water. The little box is apparently the high pressure protector.

A friend said I should check the power to the boat for bad connections, which might cause low amps or voltage, and clean the condenser fins. I found one problem with the white wire at the shore power plug and repaired it as it was causing discoloration on the shore power cord. The condenser was cleaned, a new filter installed, and all electrical connectors were removed sprayed with electronic cleaner and re-installed.

I am not sure exactly why, but the unit now works as before the problem. Thank you all so very much for your guidance and suggestions. I wish I knew which item made the difference, but suspect it was primarily, if not totally, related to the flow from the intake.
 

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One of None
Hunter 34
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Suggest you run white vinegar through the condenser: close sea valve, take hose off and fill cond from the hose with a funnel, let set a few hr's. Very possible the neutral (white) was a problem
 

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I wish I knew which item made the difference, but suspect it was primarily, if not totally, related to the flow from the intake.
That is probably what it was; insufficient water flow is by far the #1 cause of high pressure safety trips, as that is it's primary function...to protect the system in the event of lost flow.

If you can locate the water cooled condenser there will be 4 pipes connected to it; water in, water out, refrigerant in, and refrigerant out. The refrigerant pipes will be the smaller diameter ones. Feel the temperature of those pipes. The hot gas line going into the condenser should be hot to the touch, and the liquid refrigerant line coming out should be slightly warm, or even cool. If that liquid line is hot, then you are not getting enough cooling.

I teach all our apprentices to use their senses before they even touch gauges and thermometers. Feel the temperature of all the different pipes in a system when it is functioning correctly, and then when there is something wrong with it you will likely notice the difference.
 

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If your problem is/was only due to bad wiring connections and/or scale on your heat exchanger, you're a lucky guy. If so, and your system is operated very often, and particularly if you are in an area with water with much silt, the heat exchanger/coolant loop should be cleaned as a routine matter. In our case, that means annually.

To make coolant loop cleaning easier we have unions in our raw water lines that allow us to disconnect the lines from the raw water pump on the input side and the line to the through hull on the discharge side. To flush the system we connect a length of hose to the union on the input side and run that to a sink drain and a garden hose from our dock-side water supply to the discharge side of the system and pump fresh water through it in a counter flow for 5-10 minutes. The amount of junk that gets blown out can be quite amazing. Once that's done, we have a 5 gallon bucket the we fill with a mixture of RydLyme and fresh water (about two gallons) which is far more effective than vinegar (no disrespect to DeniseO30 of course). To circulate that through the system we use a small bilge pump submerged in the bucket and connected to the discharge side of the system with a short length of hose and re-direct the hose connected to the input side of the system back to the bucket. We power the pump with jumpers to our main battery bank and let it run for a few hours. One can tell it's working to eat up the mean and nasties on/in ones cooling loop by the foam in the discharge line. After several hours, we disconnect the line from the pump and reconnect the garden hose and again flush the system for 5-10 minutes or so. (All of the foregoing almost takes longer to describe than it does to actually do.) Once done, the flow rate through the system is noticeably improved as is the performance of the AC.

In the foregoing I refer to RydLyme as that is what we use. One can also use a material known as Barnacle Buster which is, roughly, equivalent and may be somewhat less costly in some areas. I am sure there are other products as well that I am not acquainted with.

FWIW...
 

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If your problem is/was only due to bad wiring connections and/or scale on your heat exchanger, you're a lucky guy. If so, and your system is operated very often, and particularly if you are in an area with water with much silt, the heat exchanger/coolant loop should be cleaned as a routine matter. In our case, that means annually.

To make coolant loop cleaning easier we have unions in our raw water lines that allow us to disconnect the lines from the raw water pump on the input side and the line to the through hull on the discharge side. To flush the system we connect a length of hose to the union on the input side and run that to a sink drain and a garden hose from our dock-side water supply to the discharge side of the system and pump fresh water through it in a counter flow for 5-10 minutes. The amount of junk that gets blown out can be quite amazing. Once that's done, we have a 5 gallon bucket the we fill with a mixture of RydLyme and fresh water (about two gallons) which is far more effective than vinegar (no disrespect to DeniseO30 of course). To circulate that through the system we use a small bilge pump submerged in the bucket and connected to the discharge side of the system with a short length of hose and re-direct the hose connected to the input side of the system back to the bucket. We power the pump with jumpers to our main battery bank and let it run for a few hours. One can tell it's working the eat up the mean and nasties on/in ones cooling loop by the foam in the discharge line. After several hours, we disconnect the line from the pump and reconnect the garden hose and again flush the system for 5-10 minutes or so. (All of the foregoing almost takes longer to describe than it does to actually do.) Once done, the flow rate through the system is noticeably improved as is the performance of the AC.

In the foregoing I refer to RydLyme as that is what we use. One can also use a material known as Barnacle Buster which is, roughly, equivalent and may be somewhat less costly in some areas. I am sure there are other products as well that I am not acquainted with.

FWIW...
Wow! If only more people went to such lengths to keep their system running at peak efficiency! Most people just run it until it stops working and then think about it! Paying attention to the temperatures I mentioned will give you a good idea when it is time for a flush.
 

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Old as Dirt!
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Wow! If only more people went to such lengths to keep their system running at peak efficiency! Most people just run it until it stops working and then think about it! Paying attention to the temperatures I mentioned will give you a good idea when it is time for a flush.
Southwest Florida in the Summer is no time to be without AC. Saturday, with the system down while I was doing some work on the electrics, the cabin temp reach 103º. One does what's necessary to keep things working reliably or does without and that WOULD NOT make/keep my (much) better half happy!
 
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