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Boat Refrigeration / Selecting Ice box conversion
« Last post by Richard on April 26, 2019, 05:18:07 pm »
We wish to install a refrigeration system and have settled on the "ColdMachine" units.
The CU 94 looks suitable as does the CU 100

I am told from one source that the CU 100 is made in USA and ahs better electronicsthan the 94.
also that the 94 is made in China

I have been over the Dometic web site in detail, but would appreciate advice and comments from experienced users
Is one of the above units more reliable than the other?
More corrosion resistant?
Any alternative 12 volt driven units by other manufacturers in that capacity range that you can recommend?
Is there a useful tech support number for the units (after 2 hours talking with nice polite, but technically illiterate sales people on several Dometic phone numbers, I have not found one)
I would like to discuss this with a couple of sailors who have installed one of these units in an existing refrigerated box.


When it comes to selecting an icebox conversion unit selecting what goes into the box has to come first. All companies that sell these units will not have evaporators that will produce the results you are looking for. Box lid opening size and size and shape of box interior will help to determine again Btu size of evaporator needed. Next decisions are you hopping to have a cooler or just a refrigeration section or a combination temperature box with a freezer area?

Selecting a single temperature cooler or refrigerator box evaporator most all of these conversion companies offer evaporators in sizes that will work even eutectic solution plates for single temperature coolers and non freezer refrigerators. Selecting evaporators for a freezing area within a box requires a evaporator or evaporators that surround the frozen food as much as possible. Once you determine what is required inside the box you can find a company that has the installation kit with the condensing unit you need.

Demedics  CU 94 unit probably is very limited in evaporator selection and their long condensing unit is not easy to locate in boat where it is as efficient as others would be.

Demedics Adler Barbour unit offers the Bin shaped evaporator allowing multiple temperatures and freezer temperature within the same box. Adler Barbour was the leading manufacture of air cooled Icebox conversion units until they started adding  marketing gadgets like the unnecessary poor structurally design external circuit board and offering electronic thermostats.

Nova Cold Has the least expensive conversion unit and a good selection of evaporators including a freezer bin.

Thchnautics Cool Blue is the best simple and only true proven reliable holding eutectic solution plate system but expensive.

SeaFrost and Cold Eh Marine both offer custom heavy duty evaporator plates and will help you with a custom design refrigerator freezer in the same box.

Boat Refrigeration / Engine Driven SeaFrost system.
« Last post by Richard on April 26, 2019, 05:06:45 pm »
This has been a very reliable system. a couple of years ago we were switching out the engine and replaced the dryers and the engine drive compressor with new. Also switched to a serpentine belt which has been a major plus.
I am surprised that engine drive systems don't seem to be in fashion anymore. They are powerful, rock solid reliable and generally repairable anywhere with air conditioned cars. Most days you are running the engine anyway and it stores a lot of energy quickly. In moderate climate with a well insulated box it only takes 30 minutes to an hour ( generally split into morning and evening runs ) to maintain the freezer and refer. If that was 2 DC units drawing 7 amps each with a 50% duty cycle that's 168 amps per day that would need to go back into batteries.
If you couple the engine drive with a separate AC / DC driven circuit for shore side its a redundant and robust system. If it were DC instead of AC not sure what I would do to improve it except for independent temp control in the refer and freezer sides.
Turns out the biggest change was not equipment but getting serious about insulating the box; wish I had appreciated what a massive difference it would make sooner.


Out of date
You are correct about engine driven refrigeration it is the best in the right application. They are powerful, rock solid and repairable. Few armchair sailors venture below Latitude 28 or plan on living a board. Because of the improvements in on board boat Direct Current power grids. The average boats with a limited size refrigerated box are generally satisfied with 12 volt refrigeration. The trouble with a few of the new 12 volt ice box conversion units is they are not considered repairable by most local refrigeration mechanics.
 A true eutectic holding holdover plate system like your SeaFrost unit in non tropical climates may require only 15 minutes engine running in the morning again 15 minutes at night. Your engine driven compressor I one hour, running at low Rpm, can produce 8 to 10 times the cooling capacity of a Danfoss BD running one hour.

The most popular ice box conversion refrigeration in the Caribbean and West Indies charter boat industry is still engine driven with true eutectic holding holdover plate. 

Boat Refrigeration / Large Pleasure Boat Refrigeration System
« Last post by Richard on April 26, 2019, 04:56:01 pm »
Just a further bit of information.  When the refrigeration man looked at the system last year he removed the Ranco O10-1416 thermostat and fitted a locally available one with only a single control knob, no proper calibration and no hysteresis adjustment.  Id like to replace it with something like the Ranco but cant find one any more.  What can you recommend?
Thanks again for your help and I look forward to your comments.  Ill be back to you with info on the insulation as soon as I can defrost the freezer.

Now to your questions and my answers:
1.   Yes but the compressor, condenser etc are fitted in a very confined space with little or no ventilation when the boat is in the water.  When we are living aboard on the hard we open up the compartment to let the air in and out and switch off the water pump.  Refrigeration performance is much reduced but we still can freeze the plates.  Should I provide permanent ventilation?
Answer 1.  The more cooling of compressor the longer life for the compressor.
2. Unfortunately I have left my contact thermometer at home in Spain so I have had to use an IR gun type thermometer.  The results I have are 31 deg C and 40 deg C.

3. Never to my knowledge. A previous owner may have done so but based on the maintenance done during the 10 years or so prior to my ownership I would say not.
Answer 3.  The water condenser needs water tube cleaned once a year.
4.   There was when I first had the boat but one of the so-called technicians said it was a waste of time and removed it.  I still have it so it could be replaced but I have to find someone to do it!
   Answer 4. You dont have to have sight glass to determine correct refrigerant when you can read amperage and see where frost cover is present.

5.   All of the vertical plate (first after the expansion valve) is covered in frost and all of the second plate is covered with a thin film of ice.  Frost builds up quite quickly and can reach 3/4 in about a week.  I cant find a major air leak though.
   Answer 5.  inch frost in a week is caused by air infiltration normally caused lid or door seal leaks. Checking these seals with a ribbon closed in various location around seal should not be easy to pull out with lid or door closed.
6.  No accumulator is visible.  (see photos).  The suction line is cold with condensation despite being insulated.
7.  8 9 amps approx. based on reading the distribution panel meter.
8.  All of the first plate and (I think) all of the second plate is solid.
9.  Frost is on both plates and the expansion valve.  The suction line seems wet but not frosted but the insulation on it is not good and is saturated with condensation.  Time for replacement?
     Answer 9. If moisture on refrigerant return line is not a problem for you do not worry about it.

10. R12 and an R12 substitute mix.  The system was topped up with R12 last year having been vented a couple of years back and refilled with the substitute.  If the technician has no more R12 then I am not sure what can be done as he assures me no R12 substitute is now available here in Greece.  I dont have any servicing equipment but would be prepared to buy some if I had some instructions on how to use it.  I now have little faith in local technicians but would need some hand holding to undertake any alterations myself.  Also how I would obtain R12 substitute gas I am not sure but could probably talk to a local a/c man in Spain where I spend my winters.

Answer on refrigerant. Running three hours to freeze plates solid and cool box down the first day is OK, but too long a running time every day there after.
Amperage if it includes the water cooling pump is about one amp low.
All plates would normally have equal frost cover unless the two with less frost are far away from leaking air seal.
I am surprised after 3 hours running time that frost is not present on line leaving refrigerated area.
Boat Refrigeration / Fridge Option Questions?
« Last post by Richard on April 26, 2019, 04:31:43 pm »
I am working on the refrigeration options in my Gulfstar 51 Sailboat-- the current setup has two separate boxes for fridge and freezer- each has two holding plates approx 16 inches x 14 inches and 3 inches thick. The system is an older Crosby unit which is 110 volt water cooled- it still works fine but we are planning on going cruising next year in the Caribbean and think we would prefer 12 volt as we have 400 wind genny and almost a kilowatt of solar power to charge batteries. Dimensions of the two boxes are as follows
fridge- 46" length x 22" width and 28 inches deep (one holding plate on each end (22" walls)
Freezer- 21" length x 15" width and 21" deep (one holding plate on each side)

both have a seperate thermostat- there is also a separate ice maker installed but i am not overly concerned with it. I believe it is a separate system with its own internal compressor etc.
In your opinion what is the best option?
1)leave the old system in place and add in a Technautics system on the blank walls of each of the boxes
2) tear out the old system completely and replace?
3) tie into the existing system by adding a 12 volt component ( not sure this is feasible)?
4) take out everything but the holding plates and reuse them?
5) something else that makes more sense to someone with more expertise than i have
Thanks in advance for informed opinions!
Usually 46 foot and larger sailboats are equipped with onboard generators and industrial type refrigeration not 12 volt refrigeration. These large sailboats almost always have on board air conditioning to prevent mildew by dehumidifying interior air and to provide creature comfort in hot weather conditions. The Gulfstar 51 regardless of the model will be equipped much the same as other boats of this size. Because these boats have accommodations for eight or more people this is why refrigerator box is so large in this boat, 16.4 cubic feet. The freezer  is 3.8 cu ft. The two refrigerator holding plates are sized for only a ten cu ft box which means compressor most run more than twice a day. The freezer plates are sized correctly for a box of five cu ft.

The main concern with refrigeration in boats especially older boats is the insulations  resistance to conduct unwanted heat. Even closed cell insulation over time can outgas the insulating gas stored in each cell allowing moist air to inter these cells. There are ways to determine if insulation is still expectable for the cooling energy available.

This boat currently has an operating refrigeration system that can answer the open question about is there enough insulation or is more refrigeration capacity requires. By reporting present compressor current draw and hours of compressor running time in a 24 hour day and adjusted for any changes in planed cruising climate temperatures, many questions can be answered.

Additional questions asked by owner:

In your opinion what is the best option?
1)leave the old system in place and add in a technautics system on the blank walls of each of the boxes?
My answer-- Yes, your boats single refrigeration system does need redundancy for a year cruising in the Caribbean. An Cold Eh Marine designed system especially designed by John without wasting space of an additional eutectic plate is a good 12 volt solution for freezer. The 16 cu ft refrigerator boxs heat load in the tropics or even in Texas is too large for any of the small 12 volt refrigeration units. Grunert refrigeration has HP 12 volt units that would solve your problem for the refrigerator cooling capacity. John at Cold Eh Marine also has a twin 12 volt Danfoss condensing unit that could supplement the old Crosby and also provide redundancy.   

2) tear out the old system completely and replace?
My answerWhen I do a worst case projection of Btu of cooling required in the tropics for both boxes you need 11,280 Btu of cooling per day. It would be difficult to remove present system and find a equal or better system that is presently designed for your application.

3) tie into the existing system by adding a 12 volt component ( not sure this is feasible)?
My answer I would need to see a picture of existing holding plates. Crosby 30 years ago used Dole eutectic plates with duel evaporator coils inside. This design of a plate makes it possible to connect another condensing unit to all plates without disturbing present system.

4) take out everything but the holding plates and reuse them?
MY answerYes it is possible but I an not in favor of it unless plates are reconditions correctly and new condensing units refrigerant flow corresponds to plates evaporator coil size insuring adequate oil return to compressor.

Boat Refrigeration / Selecting the Best
« Last post by Richard on April 26, 2019, 11:39:56 am »
My short answer to your question is describe in detail the system you have and how well it performs in various weather conditions as well as your likes and dislikes. I will then recommend more than one companies refrigeration unit.

Long answer, I know of no Icebox conversion refrigeration unit that is not suitable for some application. With over one hundred pleasure boat refrigeration options to select from choosing the correct unit requires a number of questions answered:
1. What is size of box to be refrigerated?
2. Is this a single box to be used a 40 to 50 degree F cooler, or a 33  to 36 degree refrigerator?
3. Is this box required to also have a freezing section?
4. What size 12 volt electrical power grid is on boat for generating and storing electrical power?
5. Normal persons onboard?
6. Planed cruising areas?
7. Describe planed use of boat Blue water or Live aboard?
8. I always leave insulation as the last question as it is the least important, but must be evaluated especially if it is 30 years old. I assume the present refrigeration unit is still running. Now today with old unit running can you detect any box exterior cool spots or condensation after cycling for over 24 hours? How much insulation in inches do you believe surrounds the box?

From the above answers I can project your daily conceptual energy needs.

Boat Refrigeration / Selecting and Installing Refrigeration.
« Last post by Richard on April 26, 2019, 11:36:53 am »
Attention to Correct Thermodynamics for Best Refrigeration Performance.

When you purchase and install an icebox conversion refrigeration you are responsible for its future performance not the manufacturer of the system. Only you know what temperature levels inside the box you will be satisfied with and what cruising climate temperatures refrigeration will need to operate at. Manufacturers of these systems generally list performance of their systems based on standard day 70 degree F temperatures. If you plan on operating this refrigeration in warmer climates than 70 degrees add 4% for each degree warmer to sales persons energy estimate.

There are a few basic thermodynamic rules a boater needs to understand about boat refrigeration:
1.   Cooling a refrigerated box is the process of removing box heat and process mechanical heat then disposing it as far away as possible. Some of these icebox conversion system designs ignore the fact that compressor heat must also be disposed of leaving this up to the person installing or owning unit.
2.    The first law of conservation of energy in a refrigeration system states that energy can not be created or destroyed in an isolated refrigeration system like a ice box conversion 12 volt compressor system. The source of energy for a12 volt system comes from an onboard alternator, generator or alternative electrical power, wind, solar, or shore power electric. Only the compressor converts electrical power to energy for this refrigeration system. Regardless of what the sale person may say other components of this mechanical refrigeration system can not create energy, this includes eutectic holding plate evaporators.
3.     Thermodynamics of air within a refrigerator normally air is not considered a conductor of heat but under the right density it rises or descends. The reason for this hotter air is less thinner so it rises cold air is more dense so it descends. All refrigeration systems use the rise and falling air principle inside refrigerators to create a natural tumbling convection air flow to cool refrigerator box temperature evenly. Efficient refrigerators have evaporators mounted high in the box to create natural air movement from top to bottom of refrigerated area.

Selecting and Installing Icebox Conversion Refrigeration for Best Performance.

The condensing unit that includes compressor and electronic controller is where the process and electromotive heat of refrigeration is collected for disposal. When purchasing the systems condensing unit it should be designed to remove heat to another area of the boat. In other words air that has passed through condenser and absorbed heat should not pass through condenser with the added heat a second time. Most condensing units have a fan that forces fresh air through condenser refrigerant coils and over compressor and electronic module to help cool them.
A visual check of the condensing unit will let you know if it is suitable for heat disposal where you plan to locate it. Many condensing units are equipped with air duct adaptor flanges like SeaFrost, Frigoboats Capre 50, Isotherm has one model with hose adapter. AdlerBarbour sells a adapter hose kit with adapter for better heat disposal. Most all condensing units for boxes larger than 3 cubic feet will have fan cooled condensing units although they may be with open un-shrouded forced air fans. On systems where condensing unit is located in a compartment under 100 cubic feet in warm climates without adequate air exhausting an extra compartment fan to ventilate condenser warm air somewhere else is recommended.  Water cooled hermetically sealed compressors without cooling fans need a compressor and module fan to keep compressor under 130 degrees F.
Many condensing units on these 12 volt systems have condenser coils open on one side and can be mounted against an open area. Best solution when a new system is installed a lover vent with condenser unit air intake pushed and sealed against open
lover allowing ambient cabin air to be drawn through condenser. The warm air pressurized by fan in compartment is allowed to be removed by any opening in cabinet area. Selecting a condensing unit without the ability to move heat  away to another area may only be 50% energy efficient, the first law of refrigerator thermodynamics. Attempts to increase condenser fan Cfm will not move to another area. Adding additional water cooling band aids as several companies have attempted only compromises future system reliability.
The heat absorbing evaporator is the other half of a icebox conversion unit, it is located inside the insulated box to be refrigerated.  Other than selecting a compressor with matching capacity condensing unit selecting the correct evaporator is the key to converting a useable insulated box into a full functioning refrigerator. Box size and shape will determine evaporator size before selecting condensing/compressor unit.
Manufacturers of thin plate roll bond evaporators like Alcoa Aluminum of Canada defines Btu ratings for their evaporators based on operating evaporator temperature range. Once evaporator capacity is established and controlled by capillary tube a compressor/ condensing unit can be selected to balance output of compressor to match evaporator capacity.

A full function refrigerators temperatures are more than just a drink cooler if possible it should be capable of making ice and keeping ice cream frozen solid. Other eatable materials not in freezing area will need a slightly higher temperature area. The problem with ice box refrigeration conversions is they generally have lid openings on the top making it difficult to have separate temperature zones in most converted boxes. There are many types of evaporators available to separate multiple temperature zones in refrigerator. If converted box is to have a freezer section the evaporator needs to surround frozen product. A straight thin plate evaporator or a single eutectic plate may perform well in drink coolers but not in a true refrigerator with a freezing section. Square boxes under six cubic feet normally use bin shaped evaporators to provide a freezer and refrigerator section. Large or rectangular shaped boxes are mandates for a short term storage spillover freezer.

To select the right icebox conversion hardware I recommend watching my slide show at:

Boat Refrigeration / Danfoss Module failure Causes
« Last post by Richard on April 26, 2019, 11:27:33 am »
Module failures excluding lightning strikes are generally a result of system designer pushing the compressor design envelope to far or installation of electrical wiring does not comply to compressor manufacturers good practice recommendation. Low amperage devices like these controllers require clean power direct from battery. Cheap switches, circuit breaker wire terminals and improper wire for refrigerator power can also contribute to module failures.
Boat Refrigeration / Are Eutectic plates Justified
« Last post by Richard on April 26, 2019, 11:21:18 am »
Electrical energy delivered to refrigerator is converted to Btu energy more efficiently in some compressors than others defined as higher Coefficient Of  Performance  COP.  To believe that inside any type evaporator eutectic or thin plate additional energy is created is against the laws of creating or destroying energy. You can store energy in a battery or eutectic plate but you can not create it there as some would like you believe. Pete has confirmed in his own test that his eutectic cycling plate over a thin plate evaporator will save some boaters 1/3 of an amp per hour.

If by now you are not sure which evaporator will result in the refrigerator box temperatures you are looking for either a true eutectic holding plate where compressor runs only once or twice a day, or a cycling compressor eutectic plate, or the many standard sizes of thin plate evaporators you will never have your answer.

Remember the first refrigerator component selected when considering an Icebox conversion refrigeration system is the evaporator as it establishes the various box temperature zones and what type refrigerator you will end up with. Drink cooler evaporator coolers are easy to design while refrigerator two and three temperature zone boxes are more challenging.

Other major component you must select for an icebox conversion refrigerator are the size and configuration of condensing unit which includes the compressor. One of these air cooled small system manufactures recommends their condensing unit should be installed in a large area of at least 100 cu feet. Large compartments avoid heated refrigeration process air from reducing condensing units efficiency. Most popular brands of marine refrigeration condensing units are designed to draw cooler ambient air from one large area and through differential pressure deposit warm process air to another area. Adler Barbour and Isotherm offer duct adapters for condensing units.

The last component that generally is chosen by the system manufacture is the refrigerant flow control device, Capillary tube or TXV or suction pressure regulator. All holdover type eutectic holding plates use the TXV unit with a liquid refrigerant receiver tank to more efficiently control evaporator superheat so that refrigerant completes its heat absorption inside evaporator. Capillary tube designs have always worked well for refrigeration designed to operate at normal standard day temperatures. Cap tube controls  do not react to the diminishing or expanding changes of liquid refrigerant volume when temperatures change in mobile refrigeration. Fortunately almost all refrigeration technicians around the world understand maintenance of cap tube and TXV refrigerator system. Low pressure regulator control is not as forgiving as Cap tube or TXV at controlling refrigerant flow.



Glycol and water are not a true Eutectic Solution as the specific gravity of each is different allowing them to separate over time. As long as the plate is frozen water and glycol remain as a solution. It has always been believed by those of us in the eutectic plate business that the dynamic motion of a boat will keep the solution in a balanced specific equal gravity state. Glacier Bay Marine refrigeration experimented with the so called Super Eutectic Solutions and that may have contributed to their getting out of the refrigeration business.

The refrigerated trucking industries are the ones who introduced Eutectic plates to the mobile refrigeration industry and the marine refrigeration groups. Dole a company in Tennessee built the holding holdover plates for Crosby and Grunert  as well as many private boat owners. These true brine solution eutectic plates were constructed from carbon steel using evaporator coils attached to plate inside surfaces. Doles designs eliminated inside corrosion failures by adding additional neutralizing solution chemicals. Removal of air from ice expansion space replacing it with nitrogen then permanently sealing the solution tank is why 35 year old plates are still in service today.  These Dole plate are easy to identify as they were cold galvanized gray or white with liquid fill plug welded shut.

If you freeze water inside metal tank you have stored 144 Btu of energy per pound of ice. As long as there is some ice left in tank the liquid left will be held at 32 degrees F.
If a zero degree F mixed eutectic solution is frozen in the same tank there will also be near 144 Btu of energy stores per pond of ice. The difference water ice and eutectic solution ice is in a tank is the length of time the desired refrigerator temperature is controlled..

If eutectic Glycol solution stays premixed so all of it has a zero degree F eutectic freeze point and then exposed to a temperature of 20 degrees F solid ice. This is what temperatures will actually be inside plate if compressor is not allowed to cycle normally. At minus 20 degrees ice temperature only of a Btu per pound per degree is stored so within a very short time plate temperature will reach the zero eutectic freeze point. Once at the eutectic temperature point the eutectic solution starts melting at a much faster rate than water ice alone. With loss of ice volume temperature of plate will continue to rise until ice volume is low. When ice can no longer produce needed Btu heat absorbing temperatures will rises rapidly consuming only one Btu of energy per pound per degree of cold liquid solution.
When eutectic plate on small less than 1000 btu compressors can not maintain desired refrigerated box temperatures the unit becomes a cycling eutectic plate system and no more efficient than a standard evaporator.

Energy to be stored in eutectic plates is not created by the eutectic plate as some believe. Only the compressor can produce surplus energy to store in holdover or even compressor cycling eutectic plates. The only way to justify eutectic plate refrigeration when compressor is too small is to have alternative energy wind or solar.

Boat Refrigeration / About your Boat refrigeration books
« Last post by Richard on April 25, 2019, 04:47:14 pm »
Richard can you point me to which one of your books to buy? If one just wanted a manual for troubleshooting their refrigeration?

Thirty four years ago when I wrote my first text on boat refrigeration I planed on revising the books every four years instead of offering revision updates. Over the years my books were revised five times. After 35 years in aviation engineering and maintenance and another 25 years in the eutectic holding plate business I have finally retired. 

Four year old technical books are out of date and the only a major industry like automobiles can produce currant technical printed support. The boat refrigeration business has changed from selling repairable refrigeration to marketing expendable units.

 I stopped printer from printing any more books and am trying to point out on my web site updated information on typical problems with major pleasure boat refrigeration systems. I still answer help requested emails and provide repair guidance. Of the thousands of books out there should be one you can barrow. I have a few copies left so if you truly need one email me.

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