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Boat Refrigeration / The Success or Failure of Pleasure Boat Refrigeration Companies
« Last post by Richard on December 06, 2018, 10:35:36 am »

I have seen so many changes in pleasure boat refrigeration in the last thirty years, start up companies with new design ideas that could not stand the test of time are diversifying to other product lines or going out of business.. Boats of forty feet and less generally were not designed to support energy demands of mechanical refrigeration. Refrigeration is a process of moving heat from one location to another under controlled conditions. Companies that are successful in the boat refrigeration business need to be aware of the small market for their products. If a companys business plan does not satisfy each customer with; guaranteed reliability, after market support and available access to parts anywhere experience shows that these businesses will fail.

Some pleasure boat refrigeration companies appeared to have failed because of failure to recognize their units design or manufacturing flaws and did not take corrective action until it is too late. A major fault in many company business plan is in over use of creative smoke and mirrors indicating exceptional overall performance. You will always get old untruth comments in response when refrigeration is not performing as advertised from a salesman indicating; Box insulation R value is not good enough, You need water cooling, You need an expansion valve instead of a cap tube, Holding plates store energy and are more efficient than standard evaporators, What you need is an electronic thermostat. If you believe any of the above responses are correct solution maybe you would like to buy a bridge over the ICW.

As I follow boat refrigeration comments on the web it is more Dj vu phenomenon of boat refrigeration creative smoke and mirrors advertising all over again and another short term business plan in process.   Is Randys Cool Blue refrigeration unit still the exceptional breakthrough in small refrigerated icebox conversions for boats or as the new owners marketing plan says (One more year of High School for my Son and then it's back to the land of Mexico for cheap Tacos baby..)

A marketing study once claimed one satisfied costumer will increase sells by three and just one dis-satisfied customer will discourage eleven customers from buying the product.

Remember when a salesperson claims his recommended system costs more because it is more efficient it probably will not perform as well as salesperson claims in your application. It is also important to realize refrigeration means different things to different people. After it is installed is it going to be a 50 degree F drink cooler, a 33 to 36 degree F refrigerator or a combination zero degree freezer 36 degree F refrigerator. In very warm climates freezer will require a total insulation R value of at least R30 totally dry insulation or R20 in normal 70 to 80 degree climates. In spillover applications the divider must be at least insulated to R20 with some type adjustable mechanical control of refrigerator side box temperature.

It is also important to know that in warm climates 50% of the energy consumed is by product through put remember this will decrease refrigerator performance and increase energy consumed.

Increasing Insulation from 3 to 6 inches outside the box in hot climates will improve performance by 15%. Adding insulation inside a refrigerated box will greatly improve refrigeration performance mainly because box is smaller.
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Boat Refrigeration / Danfoss Compressor is running too hot.
« Last post by Richard on December 06, 2018, 09:13:55 am »


You do not need to be an engineer to know a compressor and its electronic module is running hot. If you can not keep the palm of your hand on dome top of compressor it indicates both compressor and module are running in an overloaded condition. If this overloaded condition remains for extended periods of time module and even major system failures will result.

 Danfoss BD compressors were intended to have supplemental fan cooling. When there is a lack of heat removal at compressor and condenser keel cooler the liquid high refrigerant pressure increases and generates higher compressor heat. Compressor manufacturers provide application operating limitations on each model compressor they sell. Once a non technical operator believes a BD compressor may be running too hot he can check actual refrigerator amperage draw for his system against Danfoss specifications for unit speed and BD model compressor.

Options available to reduce Frigoboat keel cooler models Danfoss BD compressor heat:
1. Reduce compressor operating speed.
3. Add Frigoboats second air cooled condenser designer to remove heat in series with present keel cooler.
4.Supplement cooling compressor with a 50 CFM fan.
5.Make sure location of compressor area space is well vented.
 
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Boat Refrigeration / Adler Barbour Design Problem See my TECH TIP #1
« Last post by Richard on December 02, 2018, 10:44:03 am »
From time to time we find design flaws in Pleasure boat refrigeration and attempt to notify the manufacture. Adler Barbour added an unnecessary circuit board to the CU model cold machines. There are three failures occurring with this printed circuit board; crack on copper ground, 15 amp fuse mounting and telephone thermostat jack. See TECH TIP #1 on my Web Site for information on by passing this circuit board and a picture of a failed board. If a replacement board is ordered it must be a improved structurally replacement.
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Boat Refrigeration / Are new boat refrigerators better than the older ones?
« Last post by Richard on December 01, 2018, 03:04:40 pm »

Product improvements in small 12 volt refrigeration seem to be in reverse compromising reliability . Several years ago when a friend was planning an extended blue water cruise, I was asked to recommend tools and spare parts to support his old refrigeration system. Because these small air cooled systems were so reliable, I recommended only standard tool kits and two spare refrigerator parts, a condenser cooling fan and a electronic control module, for his Danfoss BD powered compressor system, . Fans back then were the only part of a system that was service life limited at 5 to 7 years of live-aboard use. Electronic control module failures were unpredictable mainly because of improper boat wiring or incorrect handling of the condenser air cooling mediums heat disposal. When installed correctly these efficient systems were so reliable that Electric-Iceman, a company in Miami 18 years ago, offered a lifetime warranty for an additional one time $25 charge. This warranty policy today, with the current generation of pleasure boat refrigeration, might bankrupt a company.
There are still several companies assembling extended life refrigeration units requiring inexpensive DIY life time maintenance. Most of the old reliable systems avoided problems associated with unnecessary water cooling and add on gadgets. Many of the old systems stood the test of time because they followed simple basic designs of refrigerant gas vapor and liquid flow with no extra electronic troublesome gadgets. There are new excellent 12/24 volt powered variable speed Danfoss compressor refrigeration systems without additional gadgets that do not leak refrigerant or have problems with refrigerant flow. In the correct applications the new variable speed compressors systems can be much more energy efficient.  In most cases, any one of the following options added to a standard Danfoss compressor system can reduce overall performance reliability:
   Fan cooled evaporators like VD14,15,16, and 15- are only recommended for drink cooler temperatures as they frequently need evaporator fin defrosting.
   Pump circulating water used as a cooling medium creates a very unfriendly and unreliable system because of pump failures, water flow restrictions, air in water intake blockages when the boat is in rough water and total failures due to electrolysis. Also a disadvantage to live-aboard boaters, is that there is no refrigeration when the boat is out of the water..
   Ice Box Conversion Refrigeration system that depends on O-rings to provide a permanent life time refrigerant seal is not a wise choice.
   Also, systems that have demonstrated more than a few serious problems, such as refrigerant flow problems are a poor choice when choosing a system.
   Electronic thermostats that are intended to control box temperature instead of a capillary tube evaporators temperature can and will unbalance a systems efficiency by overpowering the evaporator and they are more likely to fail in marine environments than manual snap action thermostats.
   Being able to adjust the compressor speed to achieve the best System Coefficient Of Performance (SCOP) is a great improvement in balancing all of a system's components. The other advantage of the BD50 and BD35 variable speed compressor is the ability to reduce the compressor speed to its best energy efficient speed, COP, for the lowest daily energy consumed, while maintaining the desired box temperature. The fact is, if your refrigeration unit, at its lowest speed, can maintain the desired thermostat set box temperature at the least daily amperage then increasing the compressor speed in small heat load boxes is not necessary. Installation of troublesome automatic speed controls is also unnecessary in small heat load boxes.
Basic boat hand tools that were adequate before creative marketing changes are not enough now with gadget loaded refrigeration systems. To cope with unfriendly gadgets such as; water-cooling problems, electrolysis, installation design flaws, refrigerant leaks, overload in electronics and contaminated refrigerant due to refrigerant line connector leaks specialized training is required. Some of these new systems are so different that there are only a few people can repair or service them. Problems of design or installation concerns or non standard parts are limited to home port system distributor. Most distributors selling the new generation of icebox conversion units will request you find on your own a qualified service engineer to repair your unit. In a remote area finding someone to work on a non standard system is generally not possible so boaters must do their own work. By ignoring problems that could be fixed or prevented by product improvements or even issuing service bulletins or typical repair instructions these organizations are forcing people to violate the intent of Federal and local clean air regulations by working on refrigeration systems without proper information.
A tooling list for repairing maintenance problems of the new generation of unfriendly systems consists of: having refrigerant 134a servicing equipment adaptable to inch serving ports and a refrigerant deep vacuum pump that is required for some system repairs . In countries where the Clean Air Act defining Montreal protocols apply, a Refrigerant recovery pump and recovery tank are also required even for 134a refrigerant repairs.
The basic assumption that a new icebox conversion refrigeration unit is better and more efficient than earlier models is generally overrated by creative advertising. When it comes to reliability and mechanical break downs, the simpler leak proof, well designed systems are more reliable. In summary; select a simple system where problems are not difficult to identify or correct yourself or the technical knowledge of a local mechanic. If one e-mail or phone to the manufacturer will not get the system back in service you may have purchased the wrong system.
     

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Boat Refrigeration / Boat Refrigeration Technical Tips
« Last post by Richard on November 30, 2018, 10:31:26 am »

Technical feed back is rarely available from small Job Shop companies even on repairable equipment like boat refrigeration. Most of us understand terms like Service Bulletins, Typical Repair Information and Equipment Recalls but where are these preventive services for a boaters expensive refrigerator. Too many expensive products today like boat refrigerators are sold and treated as expendables like kitchen can openers and toasters.
Twenty nine years ago I sold my first book on Do It Yourself Boat Refrigeration and after four additional revised books. I update my library on boat refrigeration information from email and the internet. Instead of additional books I plan on using the internet to issue Technical Tips on pleasure boat refrigeration based on Email reports and other information I receive with regards to refrigeration problems.

Tech Tip #1 on my Boat Refrigeration forum plus other tips at http://www.kollmann-marine.com. If anyone sees technical problems that may be of interest to other boaters on boat refrigeration send them to me.
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Boat Refrigeration / Plan ahead and reduce boat refrigerator down time and repair Posts
« Last post by Richard on November 30, 2018, 10:21:44 am »


If you are having trouble with your boats refrigeration unit, do not call a mechanic. In most cases you can repair it yourself. The most common boat 12 or 24 volt refrigerator compressors are made by Danfoss. These compressors are used by Adler Barbour, Frigoboat, Grunert, Waeco, EZ Kold, Technautics, SeaFrost, Isotherm and several other companies. On Danfoss BD compressors manufactured before 1996 simple tests without tools can be done to isolate the trouble which will allow the boat operator or anyone onboard to correct 90% of possible problems. But if assistance is needed it is available free at http//www.kollmann-marine.com.

After 1995 only Danfoss BD 35 and BD50 energy efficient compressors were produced. One feature on all these new BD compressors is their ability to electronically advise an operator of the location of a problem. A troubleshooting micro processor similar to an automobiles computer warning light can be installed that will flash a code that will indicate what the problem is. On automobiles an expensive test meter is required to read troubleshooting information, but on BD compressors a simple LED connected to the Danfoss control unit flashes a code. By counting the number of troubleshooting LED code flashes, repeated every four seconds, the item causing the problem will be defined.

There are five different LED signals. They are listed below.:

1.One flash, Boat wiring or battery voltage low,
2. Two flashes fan drawing more than amp.
3. Three flashes, Units amperage too high, someone has tampered with refrigerant.
4. Four flashes, compressor under heavy starting load and can not reach 1850 rpm control speed in time.
5. Five flashes, compressor running under heavy load and module overheating.
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Boat Refrigeration / Expensive Refrigeration Design Error
« Last post by Richard on November 30, 2018, 10:10:12 am »

From several emails and comments on Rparts web forum. There is a strong indication that Danfoss BD80 compressors are possibly failing do to oil starvation caused by oil pooling in oversized holding plate coils. To prevent compressor oil starvation lines must be small enough in diameter to keep refrigerant velocities up. It seems that there is no way to predict how long it will take before these compressor locks up; one system ran for two years another one year. One system had a Grunert holding plate designed for a larger compressor having a inch return line. The first indication of a problem was a compressor overload LED signal of three or four flashes. If someone has found a solution to this problem short of replacing holding plates I would like to hear from you.
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Boat Refrigeration / Replacing 36 to 46 Foot Pleasure Boats Refrigeration
« Last post by Richard on November 29, 2018, 04:10:45 pm »



 Remembering the 70s and 80s boat refrigeration was before the transition from low speed diesel engine power to the modern high speed diesel engines. Back then the larger boats 36 to 46 ft that needed refrigeration looked to Grunert and Crosby who adapted and modified proven supermarket condensing units and eutectic holdover plate evaporators from a company building refrigeration for trucks. If a boat was equipped with a generator 110 volt compressor refrigeration units with hold over plates was the answer to  refrigerator and onboard boat freezers. Boats without a large electrical power grid used 12 volt DC belt drive motors to operate belt driven supermarket stile compressors. The alternative to large electrical driven refrigeration was a engine driven compressor with an electric clutch that allowed a refrigerator thermostat to control refrigerator box temperatures. There were advantages to the off the shelf refrigeration designs. It was not a problem to find a technician with experience on conventional refrigeration. Package units had safety switches, isolation valves and leak resistance line connections set a quality standard the still exists today.
The main disadvantages were% added weight as much as 300 pounds to boat and they all required an engine to run when refrigeration unit was running.

Simple Engine driven simple water refrigeration built by individuals for there own boats were in use as early as 1969. Cast iron automobile air conditioning compressor connected to a water cooled condenser with a variation of home made hold over evaporators becoming popular boat refrigeration systems. I new a man who built his boat with one of these basic systems and after 17 years he still had the same reliable refrigeration.

I ordered a new 32 ft sailboat in 1982 and spent time visiting most of the boat shows East of the Mississippi river looking at equipment for my new boat. Engine driven refrigeration components back them looked the same as automobile air conditioning except for the need for a water cooled condenser. I showed a picture of an engine driven system to my auto shop foreman. On Monday the foreman filled the trunk of my car with the complete AC system he removed from a  wreaked 1978 Dodge Omni car, Swash plate Sanden SD508 compressor, expansion valve, evaporator and refrigerant hoses. I had a mechanic built a  box out of 304 stainless with a removable top to put the Omni evaporator in. To complete my new boats refrigeration I only had to purchase a Seawater condenser, high and low pressure switches, New refrigerant receiver filter dryer, and a 60 minute timer to operate compressor clutch once a day. This refrigeration unit with all its original Omni car parts after 15 years was upgraded to a dual  hybrid 12 volt/ engine drive system. When I sold boat the original compressor was still operating after 30 years with only drive belt replaced a few times.

There were a number of errors made in the earlier model designs of pleasure boat refrigeration prior to the year 1995:

   Automotive AC compressors came in several shapes and sizes and many failed the test of time when used as boat refrigerator compressors. The Tecumseh cast iron H1000 and 500 two cylinder compressors used a large ford vehicles were heavy and the aluminum small capacity two cylinder York all developed a pulse vibration do to longer belts as they were not mounted on engines. These two cylinder compressors had another design problem with drive shaft seal leakage. The clutch and compressor drive shaft was supported by an internal large wet bearing inside compressor caused shaft seal failures. Also the two cylinder shaft seal requires high crankcase refrigerant pressure to prevent leakage.  When these first generation two cylinder AC compressors were used in low back pressure refrigeration they were installed on large heavy Low Rpm diesel engines where compressor Rpm normally operated a less than 1600 Rpm.  In the 1970 and 1980s  it was believed by many that if an AC compressor operated OK at 6000 rpm it could also operate at the same speed for refrigeration this proved to be a big mistake. After limiting compressor speed to less than 1600 Rpm earlier failures were eliminated.
   Aluminum Swash Plate actual flow five cylinder compressors belt driven by high Rpm diesels boat engines became the reliable standard for reliable boat refrigeration. On a Yanmar 3600 Rpm engine a four inch engine drive pulley will keep compressor functioning for many years. Swash plate shaft seals do not rely on only refrigerant pressure to prevent seal leaks and the load on belt drive is transmitted from clutch bearing direct to compressor aluminum case and not to bearing inside compressor as was the problem with first generation compressors.
   Air cooled condensers are not recommended for engine driven refrigeration due to their high Btu refrigeration capacity, ten to twenty times more Btu per hour than small 12 volt systems. Engine driven refrigeration requires sea water cooled efficient cupro nickel condensers capable in tropical waters of disposing of from 6000 to 12000 btu per hour depending on compressor output. Boat engine driven refrigeration companies have been known to sell water cooled condensers that in warm seawater cause poor refrigeration performance. Source for condenser water is best provided by existing engine seawater cooling pump flow avoiding an extra electric pump.
   Expansion valve flow control valve size is important to prevent liquid slugging of compressor. For engine drive compressors that have capacities from 12000 to 24000 Btu capacity as AC units but now are  used to control refrigerant limited flow in holding plate compressor start up situations flow must be restricted. Refrigerants are condensable and in a refrigeration system will change to a liquid in a cold enough area of the system like a partially frozen holding plate. Engine is almost always running when refrigeration compressor clutch is in gauged this fast clutch action will move liquid refrigerant from holding plate quickly possibly damaging compressor that only pumps gas vapor. Design mistakes of oversize flow control devices in the past have resulted in compressor failures. Suction line accumulators help resolve liquid slugging of compressor as well as long oversize suction tubing. I still recommend small tonnage expansion valve with max orifice of  to One ton for engine driven systems.
   Large boat refrigeration systems where sufficient energy is not available 24 hours a day generally use holdover evaporators containing large amounts of a eutectic solution to store surplus energy in the form of ice. All of these holding plates are not designed the same, besides size, shape the thermo energy efficiency designed inside plates is very important. The volume of eutectic solution will determine how long plate will continue to absorb heat. The preset phase change temperature of eutectic material will determine plate exterior temperatures where heat is collected. The lower the phase change temperature the shorter the holdover period. The exterior skin material of holdover plates varies from carbon steel coated with cold galvanizes to cast aluminum and stainless steel. Cold galvanized plates are not as attractive as stainless steel. The problem with welded stainless steel is the carbon added to weld areas by Tig welding can over time allow plate solution to leak out. Food stainless steel serving trays have been used by a few manufactures as holdover tanks with backs welded or bolted with gaskets to seal liquid in. Cast aluminum box plates also had bolt on plates with gasket material. The eutectic material inside plate needs to be non corrosive and food grade non toxic should material leak into refrigerated area. Inside all these holdover plates there is a refrigerant evaporator coil to collect the refrigerator heat. These special evaporator coils are not all as efficient as you might thank.
   Refrigerant hoses instead of metal tubing was a major mistake because of  refrigerant leaks and moisture migration through flexible hoses. Moisture osmoses penetration into a hose when refrigerant did not leak through hose is hard to believe but it is true according to the hose manufacturer. Prior to 1995 boat refrigeration systems with rubber hoses were plagued with moisture freezing in expansion valves. Systems with all metal tubing did not experience moisture problems. Another trouble with hoses was their aluminum hose fittings would leak and even break into dumping all refrigerant.
   Copper nitrogen filled tubing is used throughout a system except near compressor where short vibration dampening copper line or very short section of hose is needed to prevent work hardening copper line failures.
   Refrigerant copper line connections on most of the older large pleasure boat refrigerator kits were hard silver brazed or soldered permanent connection. With the exception of evaporator plates and thermostat, all refrigerant components were mounted on one or two base plate assembles. When these major components were connected together Refrigeration grade flared brass connecters were  used as they will remain leak proof under thermo expansion better than any other mechanical connection. Systems that used other light weight mechanical connections eventually had refrigerant leaks.


There are boats in the 36 to 50 ft range that still have these twenty to forty year old supermarket style refrigeration and Engine driven units in there boats.  The trend seems to be to remove highly effective large refrigeration and replace them with very small 12 volt DC units. Experience has proven that without an onboard generator BD size 12/24 volt compressors in warm or hot climates are not adequate in Freezer boxes larger than four cubic feet or refrigerator boxes over six cubic feet.  The real question in this post is how large a box can be refrigerated by a 12 volt DC hermetically sealed compressor?  There are always comments suggesting the answer is to add insulation and not Btu capacity.   Insulation has never been a solution if boat is to be a live aboard in the tropics unless adding insulation is to reduce size of area to be refrigerated.
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Boat Refrigeration / Adler Barbour CU100 with a five LED Flash Code
« Last post by Richard on November 29, 2018, 03:48:42 pm »
QUESTION:
Im getting 5 blinks on my cold machine. I have plenty of ventilation and have powered the system down and then up and the 5 blinks occur immediately. How much for a new module if this is what is needed. Thanks much.

ANSWER
Five flash LED code is generally not a sign of module failure. Adler Barbour  CU100 and CU200 models have an additional unnecessary poorly designed printed electrical board. These electrical boards have three troublesome problems the board itself is not structurally strong enough, and the 15 amp fuse holder overheats and its contacts burn. The third problem is with the thermostats connection to board using a phone jack instead of a hard connection. The First place I would recommend be checked on a CU unit with a trouble code of 3,4,5, or 6 LED flashes every four seconds is to visually look at back of circuit board inside add on stainless steel box for heat damage. See picture on  TECH TIP #1 at my web site front page.  Also check for lose or corroded connection at both ends of refrigerator ground wire. If there is some problem with printed circuit board read complete TECH TIP #1 for corrective action options.

My standard troubleshooting steps for Danfoss BD compressors are:

Three and Four pin Danfoss BD troubleshooting
 
If your refrigeration unit is over 10 years old and has a Danfoss BD 2 or BD2.5 or BD3 compressor then it has the older discontinued electronic 4 pin module.
Troubleshooting Danfoss compressors with 4 pin modules will consists of the following steps:

1. All of these compressors have a 4 pin module connector and their modules contain an external fuse. If this fuse is blown there are two reasons why either power wires to module are reversed or module has an internal failure.

2. Check to see that there is actually power at the refrigerator control module.

3. Place jumper wire across thermostat terminals on electronic module, Compressor still does not run go next step.

4. Disconnect black fan wire from electronic module, Compressor runs, replace fan. Compressor still does not run after fan ground wire is disconnected, go to next step.

5. Run correct size and correct polarity jumper wires direct from a fully charged battery in order to bypass all boats wiring. Volt meter readings are of no value when looking for voltage spikes. Compressor still does not run electronic module needs to be removed and tested on another unit. If there are no other units available to test your module on I will test all 12 volt Danfoss control modules free except for BD80 compressor modules. Small 12/24 volt boat refrigeration using Danfoss compressors manufactured after 1996 will have a BD 35 or BD 50 variable speed compressor with a troubleshooting computer chip built into their control module. Trouble shooting LED will only flash if electronic module sees a voltage or amperage problem. In each case problems of compressors failures to run are identified by Counting number of flashes of LED:
   No LED flashes would indicate either thermostat is open or no power to module.
   One LED flash and a 4 second pause indicates a boat wiring electrical resistance problem or low batteries. Because of modules sensitive to milliseconds of a voltage spick they cannot be detected by a voltmeter. Solution is to bypass boats wiring till problem is located. To isolate trouble follow instructions above in item number 5.
Two LED flashes indicates fan over current cutout. If fan circuit on these variable speed compressors exceeds amp compressor start up will be aborted. This condition can be confirmed by disconnecting Black fan wire at module if fan runs replace fan.
   Three LED flashes indicate excessive torque is required to start compressor. This is commonly caused by turning compressor off and back on too quickly or too much refrigerant or poor condenser cooling. Most people jump to the conclusion that there is a mechanical rotor lock up inside compressor and this is a mistake on Danfoss BD compressors.
   Four LED flashes indicate compressor motor not reaching sustained controlling speed above 1,850 rpm quick enough.
   Five and six LED flashes indicate a weak power or ground wire connection. On Adler Barbour CU models 3,4.5. and 6 LED flashes can indicate bad circuit board in stainless add on box.
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Boat Refrigeration / RV Cabinet Refrigerator performance installed in Boat
« Last post by Richard on November 28, 2018, 12:20:36 pm »

E Mail recieved
I hope you can help me with some advice.
I've recently bought a boat with a Novakool RFU6200 installed (2 door upright).
In hot weather it runs constantly and has problems keeping things cold.
Part of the reason is that there is not much venting so I'm going to cut a few more holes and install a fan to push cold air over the back of the fridge.
Just now when I pulled the fridge out of the cabinet I noticed that the pipe which comes out the top of the DB35F compressor and runs to the evaporator plates in the fridge and freezer has ice on it. The rubber which goes around the section of pipe (1' out of the compressor) has ice build up on it, which then melt when the fridge cycles off and then re-freezes. Do I need to cut the insulation off and reinsulate this section of pipe? or does it indicate another problem?

Also I thought of a few other potential improvements but am not sure of there value.
1 - install a digital thermostat to give more precise control
2 - there are air voids in the cabinet on the sides and top of the fridge. Would filling these voids with foam insulation help ie reduce chance of warm air pockets + improve insulation of fridge?
3 - replace the power module with one of the Danfoss AEO units?

Any advise is appreciated.
Thanks


ANSWER
If you put a refrigerator designed for the RV industry in a marine environment its performance may be compromised. You did not say where boat is cruising but if the ambient air temperature is much above 75 degrees F a two door six cu ft refrigerator with a BD35 compressor is not going to demonstrate great performance. 

The only information you provided that indicates a correction is needed is it has problems keeping things cold. If compressor never cycles off and box isnt getting cold enough has nothing to do with thermostat. Knowing what compressors preset speed is would help. You can contact the factory and find out compressors current Speed or check resistance of thermostats wiring circuit. With no resistance in thermostats circuit compressor would run at 2000 rpm if there is 1500 ohms compressor is running at max 3500 rpm.

Compressors that run continuously under load would indicate poor condenser cooling producing high side pressure. High liquid line pressure on these small capillary tube systems tends to decrease evaporator efficiency by moving refrigerant heat absorption beyond evaporator forming frost on line returning to compressor.
Q&A
1 - install a digital thermostat to give more precise control?

Your unit is designed to operate correctly with the thermostat it has. A digital thermostat would be a mistake.

2 - there are air voids in the cabinet on the sides and top of the fridge. Would filling these voids with foam insulation help ie reduce chance of warm air pockets + improve insulation of fridge?

Most of the cabinet refrigerators have poor control of condensers cooling medium. Some of these units use static airs natural movement up back of cabinet to remove process heat others use metal of cabinet to dispose of heat.  I am guessing your unit has a fan cooled condenser and either it is full of dust or its air deflecting shroud is not designed to properly dispose of condensers heat.  The best way to improve your units performance is to fid a way to better control waste heat disposal.

Added insulation is required only when boxs exterior temperature is more than 4 degrees colder than ambient air surrounding refrigerator.


3 - replace the power module with one of the Danfoss AEO units?

Investigate current compressor speed first and with energy already being wasted as indicated by frost outside refrigerated area I would spend my time on improving condenser cooling and Door Seal contact.. Also See section on Nine Ways To Use Fans.
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