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DIY Smart Non Destructive Refrigeration Knowledge .

I have been asked many times over the last 30 years to recommend a repair person experienced in repair of pleasure boat refrigerators. These days there are over 100 different fractional horse power 12 volt refrigeration configurations in boats under 50 feet. To find a person with experience on all small refrigeration units is not possible. There are no licenses available to qualify a person to accomplish a repair to a malfunctioning small boat refrigerator. Manufacturers specific training on each model or previous experience is necessary to repair these small 12 volt units. Each week I see where a so called HVAC trained technician or an Automobile AC mechanic screw up a good small pleasure boat refrigeration unit do to their lack of the right knowledge.

I have spent sixty of my eighty years assisting mechanics and operators of equipment in Do It Yourself troubleshooting and repair. Most of the time DIY is the only or smartest way to keep something operating.  If a boat owner understands a few simple facts he or she can save on costly repairs and in many cases avoid purchasing a new refrigeration unit. Before allowing anyone including yourself to touch a malfunctioning refrigeration system powered by a Danfoss 12/24 volt BD compressor you should know these facts:
   If This BD Compressor does not run it is because the control module sees and electrical current out of normal limits and to protect compressor from an internal failure control stops compressor. After electronic control module detects amperage loads or voltage out of predetermined limits it will stop compressor from running until problem is corrected. After stopping compressor module will attempt a restart every 40 seconds to determine if problem is corrected.
   Most important trouble shooting item to remember about Danfoss BD compressors is, If compressor will not run problem is electrical. Only if compressor runs with little or no cooling is it safe to assume refrigerant volume or its flow is the problem..
   Danfoss BD compressors manufactured after 1995 are three phase variable speed allowing balancing of system performance reducing energy consumption. These compressors are identified by model numbers BD35, BD50 and BD80 they also have ability to identify problems by an LED fault code if compressor fails to start up and run.

LED will or will not show all problems.  There are things you should know about Danfoss BD refrigeration that most repair people dont know about your Adler Barbour , Frigoboat or other type refrigeration units. This applies to Danfoss BD compressors installed after 1995. Troubleshooting the newer Danfoss variable speed BD compressors when equipped with troubleshooting LED is easy if the following information is understood:
   LED will not signal if there is no power to Danfoss Control module.
   LED will not signal if thermostat circuit is open.
   LED will not signal if compressor is running continuously with poor or no cooling.
   LED will not signal if system is low on refrigerant, compressor will run with little or no refrigerant and still no LED signal.
   LED will flash 3 times every 4 seconds if there is too much refrigerant in system or poor condenser compressor cooling.
   On Adler Barbour CU100 and CU200 LED will not flash when compressor stops do to a problem inside the add on stainless box. This seems to be caused by poor solder connections to fuse holder or cracked printed circuit board. See my TECH TIP #1 on my web site.
   If no one has tampered with refrigerant and refrigerant flow is blocked, compressor will not stop nor will LED flash on this type system. Common problem on Frigoboat keel cooler systems when refrigerant flow is restricted. Adding refrigerant will only cause additional problems. Ask Frigoboat US for help.
   If there is too much refrigerant or contaminated refrigerant compressor will not start or run signaling with Three LED flashes.
   Unlike automobile computers Danfoss electronic modules micro chip only has space for one trouble memory. Because only one memory is all that can be stored it is possible for a second problem to mask over signal covering up the first LED signal code. Say the first signal is do to a low voltage giving a one LED flash every 4 seconds, compressor will stop and try to restart in 20 to 40 seconds. If refrigerant pressure has not equalized in this short off cycle a restart attempt can cause a three LED flash signal indicating an overload. When a three LED flash is indicated always confirm it by turning refrigerator power off and while watching LED turn power back on. The first seen signal code is where the problem is.
   A faulty ground between module and main battery buss has been known to signal 3, 4, and 5 LED codes.

   Low or no refrigerant at all will not prevent this compressor from running.
   Because this compressor is silent the only way to confirm it is running is it will be warm to the touch after it has been running for 20 minutes or longer.

   Very rarely will you find a service tech who will take the time or be able to service these small units with refrigerant correctly because variations in ambient air or water temperatures as well as system design affect refrigerant charge. 
   Service technicians and helpful friends rarely practice non destructive testing when they first approach a refrigerator problem. One way to know if someone does not know what he is doing is if he wants to check refrigerant pressure. Tampering in any way with refrigerant on these small systems that my hold only from 3 to 4 ounces of refrigerant generally leads to disaster us conditions at some point in the future.
   It is important to know these that small icebox conversion units are not mass produced in a quality controlled atmosphere like standard home refrigerators. Rarely are their filter/dryers large enough to capture additional moisture over what was generated in manufacturing process. There is always a risk of moisture contamination when tampering with servicing ports. Even purging gauge sets with refrigerant before use will not eliminate all cosmoses embedded moisture from gauge set hoses.
   Danfoss BD compressor Ice box conversion refrigeration systems will not lose refrigerant if properly designed and installed correctly. The exception to this fact will be when line connector O rings are used as final refrigerant seal.

Boat Refrigeration / Two Questions Tampering With Refrigerant and Battery Life
« Last post by Richard on April 09, 2018, 11:36:37 am »

 The technician added "some gas" last week. I did not have any data so it was added just based on the feeling. Then 3 days ago I connected an ammeter and saw it 5.3 amps (I did not know what it was before) . I also observed ice on the return tube just after insulation. This was typical sign of overcharged gas based on your info. So yesterday I disharged "some" amount of gas. The amp went down to 4.3 and the compressor is not running non stop any more which was my problem. And after several hours, the main compartment was at 6 C.

I had an issue with my battery charger now it was fixed, maybe this was another problem independent from the fridge. Anyway it is good idea to check the batteries' capacity. Can you pls give some details about the test, what to measure how to measure and how to evaluate the results?

I find it is generally a big mistake to have anyone tamper with refrigerant or even connect gauges to one of these small compressors. Non destructive testing must be done first to confirm that refrigerant is or is not a problem. Amperage draw and where there is frost and confirmation that compressor is actually running is all that is needed to evaluate refrigerant quantity and flow.

I do not know what your original problem was or what unit you have but it sounds like a Danfoss BD compressor amperage range.  For anyone to help you we need to know who made this system and compressor model number and age.. If this is a variable speed Danfoss compressor air or water cooled? There are inherent problems with each type system and each manufacturers designs are different.  Amperage draw is always predictable within a given range if speed size of compressor are known.

As to battery capacity it varies with age, charging rates and total of amps through put over time. When purchased a battery it will have a diminishing amp-hour capacity over time. The rate of battery amp-hr capacity loss can be measured in how quickly it is recharged or how quickly it discharges with a fixed load. An inexpensive new group 27 deep cycle wet cell battery will lose 70% of its amp-hrs in use on a charter boat in 26 weeks if used as the house battery. The more expensive the battery we should expect and do get more daily discharges. If you remove less than 30% amp-hrs of a fully charged battery daily you will greatly extend its life. Abuse a battery you shorten its life. Battery age alone shortens its amp-hr life.

There are several ways to test how much capacity is lost in a battery.
1. Using a standard automobile 100 amp load tester that is available from parts stores is one way to evaluate a battery. Harbor Freight has them for around $30. If a fully charged battery will carry 100 amps for 5 to 10 seconds while needle stays in the green it is still good but this test will not confirm available remaining amp-hr capacity.
2. Battery voltage and length of time to recharge at a given amperage will tell you when batteries need to be replaced.
3. There are Invertors that have a low voltage cut out that can be used to test remaining battery life/capacity. When testing 12 volt refrigerator stress on battery life connected to shore power I used a Heart inverters test procedure and an old electric 110 volt clock and two 60 watt light bulbs. With inverter connected to a fully charged 12 volt battery and two 60 watt bulbs and analog clock set to 12:00 was their recommended test. When power was applied both lights and clock where operating. When DC voltage at inverter reached a low of 12 volts it shut down with clock showing hours. Using 120 watts consumed per hour from bulbs and inverter clock running time service life of battery can be determined.


The boot up test circuit in module works much the same as in booting up a computer. During the module boot up sequence it checks starting amperage peak, Voltage spikes high and low it also tests fan cooling amperage. When there is a fault detected in this electronic module protection circuit you will hear a beep as power transistor switch opens power circuit in module preventing compressor from starting. Fan will always start and stop running during compressor normal and false start attempts. 

A compressor identifying an electrical problem will try to start compressor every 30 to 60 seconds until problem is corrected. If you followed my troubleshooting steps correctly; Disconnected black fan wire, eliminated all boat wiring by powering module with positive and negative jumper wires direct to a fully charged battery then and only then would  the electronic module be questioned. Conditions like no Compressor start up are normally caused by a weak circuit breaker, Old boat wiring or any corroded wire connection. Be sure to also check fuse holder contacts in module for signs of dirty overheated condition.
Boat Refrigeration / Thin Plate Evaporator Versus Holding Plate Evaporator
« Last post by Richard on April 06, 2018, 03:29:05 pm »
It is true that many boaters assume that holding plates are more efficient than thin evaporator plates. Compressor manufacturers calculate the different  Coefficient Of Performance of each compressor example, Danfoss reports the BD50 compressor has its best ASHRAE  COP rating of  1.38 watt at -4 degree F temperature output.  A COP of less than 1.0 indicates watts of Btu energy coming out of compressor is less than watts of incoming power to drive compressor this then is less than desirable performance. The higher this ratio the more efficient the compressor will be.

The efficiency of condenser and evaporator also need to be efficient if total System Coefficient Of Performance is to be as good as compressor COP.  If the condenser design is poor or incorrectly installed in boat the compressor COP is reduced do to higher refrigerant pressures.

To answer the question how the standard evaporator can be more efficient than a holding plate. If icebox conversion holding plate evaporators are cut open you will see why many of the plates will have a negative less than one COP. Thin plate evaporators when selected to match the Btu capacity of compressor and design application capacity can be very efficient. The efficiency of any type evaporator will also depend on the pre adjusted refrigerant flow.

Boat Refrigeration / Understanding Boat Refrigerator Plates
« Last post by Richard on April 02, 2018, 11:46:48 am »
Thermo plates, Power plates and holding plates are all evaporator plates. The evaporator in a refrigerator is where liquid refrigerant is converted to as gaseous form of vapor absorbing heat as it changes. If a compressor has available surplus energy holding plates are sometimes used to store that surplus energy for use later. Power and Thermo plates store only small amounts of energy. Of all the different types of evaporators the standard evaporator maintains the best even control over box temperature.

Power and thermo plates help to smooth out the compressor stop and start run times but store very little Btu energy.. These small 12/24 volt compressors generally do not produce surplus Btu to store in holding plates unless boat is equipped with alternative sources of power from Solar or wind generation systems.

As far as a blue-water sailor is concerned it is only on the first day when refrigerator system is turned on will you see a difference in the different evaporator types. The standard evaporator begins to collect a very thin layer of frost after 15 minutes compressor running time. Thermo and power plates will take a longer running time to develop a frost cover. Holding holdover plates designed for freezing temperatures with cap tube flow control will take from 2 to 24 hours to freeze all of the eutectic solution, for this reason large holding plate systems use Thermo Expansion Valves instead of cap tubes.

In my thirty six years experience with manufacturing testing eutectic holding plates leads me to believe only a few plate designs would  have the COP as high as a roll bond thin aluminum evaporator plate. I have opened eutectic plates to inspect them from Frigoboat, Glacier Bay, Technautics, SeaFrost and Dole. Dole has probably built more pleasure boat refrigerator holding plates than any other company in the US. Dole I believe to have the most efficient plates for these reasons; True eutectic brine corrosion resistant mix solutions, Two independent evaporator coils mechanically attached  to exterior steel cold galvanized tank for quick thermo heat conduction between steel refrigerant evaporator tube assembly and warm products inside  refrigerated box. The solution in a Dole plate does not need to be frozen solid for heat to be extracted from box.

Most companies holding plates are designed to allow solution to freeze first on evaporator coils. Ice continuing to form around and away from coil reduces the rate of heat removed from area to be refrigerated. Companies that experiment with so called Super Eutectic Solution have problems. The companies that use Glycol and water eutectic mixtures eventually find poor plate performance because over time Glycol will separate from water and settle to the bottom as a jell substance.

 Why boot up voltage protection? The answer is to prevent compressor failures do to a faulty refrigerant designs or an improperly installation in a boat. One of the modules compressor protection functions is to insure correct clean voltage to the rotation electronic that control armature rotation inside compressor. Another safety protection is to determine if compressor and condenser cooling fan is not drawing excessive amperage. The third safety boot up protection is compressor amperage draw and compressor speed at start up. The modules Boot up protection is much the same as your computer boot up by first testing to see if mouse and key board are functioning before computer can be operated. If you have Supermans eyes to read module voltage and amperage you might see the same fast short duration electrical transients out of limits reading module shuts compressor down at. I hope this explains why I suggest leaving voltmeter in tool box and bypassing all boat wiring to module before condemning or purchasing a new module.

The weak link of these brush-less lifetime compressors is the electronic control module. If the system manufacture screws up the system design or someone puts too much refrigerant in a unit or this mobile refrigerant unit is incorrectly installed control module will fail before compressor fails. Lightening Strike failures are the exception even if boat is not hit directly Danfoss engineered modules will fail.. For those cruising in South Florida or Bahamas a spare module onboard is a good idea. The number one and two reasons for module failure are module is not connected to main battery busses and compressor is operated under too heave a load. Hard start (soft slow start) modules available are just a band-aid and not a long term solution to module failures.
Boat Refrigeration / Replacement Modules Danfoss BD 4 pin compressors
« Last post by Richard on March 29, 2018, 07:38:45 pm »

I am sorry my overseas supplier went out of business so I no longer have replacement modules. Danfoss stopped making 4 pin modules for the older fixed speed BD compressors twenty years ago. Adler Barbour and Frigoboat were selling these 4 pin modules. Adler Barbour did not have much luck with their modules but I believe Frigoboat US still sell them. catalog still lists 4 pin module replacement. I got an email from someone last week who said he got a used one on EBay.

Danfoss made several different types of 4 pin 12 volt modules through the years so you do not need to buy one that looks just like yours. The newest 4 pin is much smaller than yours but it works the same as the older model like yours.

When looking for a replacement  it must be 12 volt and not 24 volt and have a 4pin compressor plug like your old one. There is no way to know if a used 4 pin module is really good until it is connected to your compressor.

I still will test your module free but you must pay shipping both ways. If your module is not blowing fuse on module it still may be good.  Have you followed my recommended tests?

Troubleshooting 4 pin modules consists of the following:

1. Place jumper wire across thermostat terminals, Compressor still does not run.

2. Disconnect black fan wire from electronic module, Compressor runs replace fan. Compressor still does not run after fan ground wire is disconnected. If one of the 10 transistors in this fan fail it can cause module to prevent compressor from running.

3. Run correct size and correct polarity fused jumper wires direct from a fully charged battery to module in order to bypass all boats wiring. Volt meter readings are of no value, Compressor still does not run electronic module needs to be tested on another unit.

If your shipping address is in the US I will test your module on my Danfoss compressor refrigeration test stand.  This test stand will run at max compressor load for a one hour. I will  then return your module to you for a shipping and handling charge of  $20.  Ship module with return address and a personal check for $20 to:

Richard Kollmann
670 Heather Stone
Merritt Island
FL. 32953

Unless someone has connected 12 volts direct to compressor the module is defective. There is no test for compressor. If my new module does not solve your problem you are only out shipping costs both ways. Modules are shipped insured Priority address in USA

Boat Refrigeration / Refrigeration Design Part #2
« Last post by Richard on March 04, 2018, 03:11:56 pm »
All mechanical designs of a refrigerant system must address possible excessive liquid refrigerant and oil returning to compressor. There must always be some assurance that accumulation of liquid will not reach and damage compressor pistons. Large systems have suction line accumulator containers to capture liquids and then slowly return them in vapor form to compressor. Small systems with Roll bond evaporators have circular traps near the end of refrigerant�s flow through an evaporator that serve as, liquid control accumulator traps. Most icebox conversion units incorporate longer than needed refrigerant lines between condensing unit and evaporator that allows liquid refrigerant to return to vapor eliminating need for a discharge accumulator. Not all evaporators are designed with suction line accumulators so if return line is less than 10 feet there is a possibility of liquid slugging compressor.
Control and Monitoring Additions
I have defined a reliable basic icebox conversion unit parts list Kit it will  still require a compressor control module, thermostat, compressor speed control and condenser fan.
�   Compressor Electronic Control Module:  There are several modules types available for the Danfoss variable speed 12/24 volt BD compressors.
Standard 12/24 volt electronic module:101N0210 was improved and replaced with new 101 N0212 module.
AC/DC module: design when power supply can be either or both AC/DC. This module is recommended if boat is to spend time connected to ships generator or shore electrical power.
EMI: Electro Magnetic Interference module recommended to reduce radio noise when refrigerator is running.
AEO Adaptive Energy Optimization module: AEO changes compressor speed automatically to find most energy efficient speed while maintaining preset desired box temperature. Highly recommended for boats where increased compressor speed at times is not fast enough to maintain desired box temperature.
�   Thermostat Temperature Control: There are four basic types of mechanical thermostats used in pleasure boat refrigeration: Zone or area thermostats for coolers and spillover boxes, Refrigerator, Freezer and full range temperature controller with adjustable differential. Electronic thermostats are not recommended in pleasure boat marine refrigeration applications due to their reliability.

Cooler and Spillover Thermostats:  Require a thermostat with its temperature sense tube  in free air space and not touching holding plate or evaporator. Use a +6 degrees F differential and temperature thermostat range from +27 to +50 degree F. This is also a good spillover thermostat range for controlling temperatures in refrigerator side of the spillover box.

Refrigerator Temperature Thermostat Controlling Evaporator Temperature: This Snap action standard manual thermostat control evaporator with a  temperature range from -13 F to +32 degrees F is recommended. Differential will range from 8 degrees, at dial setting, with the thermostat set to max cold

 Freezer temperature thermostat: This recommended thermostat for icebox conversions with standard evaporator temperature control. use a temperature range thermostat of  -26F to +5F with a Differential of  20 to 13 degrees F.
 In many cruising boats it is desirable to have a full range temperature box so it can be used at times as a freezer or refrigerator or even a drink cooler. The best full range mechanical thermostats are listed as Temperature controllers with an adjustable range of  -15 to +40 degrees F and an adjustable differential from 5 to 40 degrees.

�   Box Temperature Thermometer: With the exception of drink coolers checking temperature inside boxes with remote thermometers is desirable. Electronic temperature gauges are inexpensive but generally have a limited life on a boat. Mechanical temperature thermometers can be calibrated to perform well but are limited to where they can be installed.   
�   Condenser Cooling Fan : Condenser process heat disposal and refrigerant liquid high pressure are controlled by condenser fans efficiency. Fan amperage if monitored by compressor control module to prevent compressor overheat damage. If module detects high amperage above � amp module will prevent compressor from running. Ambient air interring compressor is normally considered to be standard day 70 degrees F so a kit manufacturer might for sound level purposes use a 35 Cfm rated 12 volt 4.68 inch muffin fan. This size fan is used to cool many types of computer electronics. They are available in ratings from 35 to 130 Cubic Feet per Minute (CFM). Air from condenser fan is also required to help remove heat from compressor. If condensing compressor unit is to be located in a warm engine compartment or when it will spend time in a tropical climate conditions a larger noisier fan is recommended. Fans that produce 80 and higher cfm can not be considered if amperage exceeds � amp due to module high amperage temperature protection. Danfoss BD variable speed compressor will run on 12 or 24 volts but the fans will always be powered by module at 12 volts.
�   Electronic Speed Control: Can be fixed by a single resistor in thermostat wire or automatically with electronic plug in circuit boards. Selecting the correct compressor speed will result in an energy efficient system.
�    Built in electronic troubleshooting LED:  A trouble analyzer Light Emitting Diode (LED) costing $2 is not included in many Danfoss refrigerator kits. It is important to install trouble LED even it may never light up. If this starts flashing a code every it is telling you why compressor is not running.

Boat Refrigeration / Design Your Own efficient Icebox Refrigeration Part #1
« Last post by Richard on March 04, 2018, 03:10:34 pm »
In most cases when you are considering refrigeration for your boat you become the design engineer and application engineer. Icebox conversion refrigeration systems are not all the same and there are no two boat installation application the same. There are a dozen brands of conversion units offering over one hundred options to select from. Boat show refrigeration displays sometimes even with operating units provide a general idea of what a system looks like. When communicating with a refrigeration brand salesman general installation information is given by someone who has not looked inside your boat and may not really understands the degree of refrigeration you are looking for.

After installation 50% of the actual refrigerator performance is a result of system design. The other 50% is how unit is installed in your boat. Advantage of visually seeing the compressor condensing unit allows you to determine if it is compatible with your boat�s design. The principle of refrigeration is to remove heat from cool area inside a box and exhaust heat to another warmer area. On most boats under 36 feet the compressor condensing unit will be installed in a cabinet or under a seat and not in a large open well ventilated area. For the compressor condenser to function efficiency it must be capable of drawing in ambient boat air temperatures and forcing warmed process air to another area. Fan cooled horizontal air flow condensers are usually recommended. Keep in mind the length of refrigerant lines between condensing unit and evaporator will vary with each manufactures conversion brand.

No longer does one icebox conversion refrigeration system work for all temperature conditions and all box sizes.  Understanding component selection when buying or building an ice box conversion refrigeration system is important. When selecting a refrigeration system knowing the size and shape of a box must come first. The average home refrigerator today is 16 to 20 cubic feet is separated into cooler, refrigerator, and freezer temperature zones. Not all foods benefit from the same stored temperatures so when considering an icebox conversion the type of evaporator and its location is important. Box insulation is also important to avoid box exterior moisture condensation while operated at the lowest box desired interior operating temperatures. Moisture on the insulation�s exterior indicates the amount of insulation is not sufficient.

 When considering 12/24 volt refrigeration for boats under 36 feet the average daily amperage and Btu per cubic ft of refrigerated space needs to be determined. Converted space of a refrigerator with insulation R value of 20 at ambient temperature of 70 degree F will require 5 amp-hrs per cubic foot a day. Increase the insulation to R30 value in tropical weather of 90+ degrees F the daily amperage will be increased to approximately 10 amp-hrs per cu ft per day. These power estimates allow for a twenty degree F freezing area using 20% of box area, If lower freezer temperatures are required additional daily amperage and Btu�s will be required.. Yes, these estimates exceed boating industry advertised figures as they represent the average blue water tropical climate cruising boater experiences.

There are four main components of an ice box conversion refrigeration system; compressor, evaporator, condenser and refrigerant flow control device. The volume of heat per hour in worst case removed from each cubic foot of refrigerated box to maintain recommended standard refrigerated box temperatures might be 600 Btu and 1200 Btu for each cubic foot of freezer volume. Worst case refrigerator designs apply to boats operating in latitudes below 25 degrees. Boats in cooler temperature climates averaging 70 degrees F can cut my figures 2% per each degree ambient day temperatures cooler than 90 degrees F. Example 70 degree average climate temp versus worst case 95 degree amperages and Btu projections are reduced by 50%.

After determining Refrigerated box in worst case daily Btu requirement and maximum amperage selection of compressor�s size is easy.  When using the Danfoss 12/24 volt older fixed speed fixed Btu compressors BD2.5 and BD3 one size had to fit all sizes of refrigerated boxes. If compressor was too small or too large for a fixed speed Danfoss it was energy inefficient. The newer variable speed BD compressors can be matched to the box�s daily heat removal load requirement by selecting the most energy efficient compressor speed. All three Danfoss variable speed compressors are Btu rated at various speeds and evaporator temperatures. I believe a fair comparison of each refrigerator�s performance is when, evaporator temperatures are maintained at +12 degree F.
 Btu output and best Coefficient Of Performance (COP) of each compressor are available from Danfoss:

These hourly figures are believed to represent a good comparison with an evaporator temperature of Plus 10 degree F (- 12 degrees C) and a condensing gas temperature of 131 degrees F (55 Degrees C) 

BD35 at 2000 rpm 214 Btu and COP of 1.4 and 3.1 amps.
BD35 at 3500 rpm 349 Btu and COP of  1.28 and 5.38 amps.

BD50 at 2000 rpm 273 Btu and COP of 1,31 or 1.74 and 4.18 amps.
BD50 at 3500 rpm 535 Btu and COP of 1.23 or 1.64and  7.8 amps.

BD80 at 2500 rpm 471 Btu and COP of 1,66 and 6.9 amps.
BD80 at 4400 rpm 936 Btu and COP of 1.51 and 12 amps.

Note These are ASHRAE  Engineering Charts

The higher the ratio of COP energy consumed by compressor the more efficient it will be. To realize the total Systems Coefficient of Performance (SCOP) the other three major components must be in close equilibrium balance to compressor�s output. Size of all refrigerant piping (copper tubing) through out the refrigeration system will be  established by the size of the suction refrigerant return line fitting at the compressor. Danfoss BD compressor return gas fitting can be either Metric or Standard for � inch outside diameter copper tubing. Some systems may use 3/16 OD tubing for high pressure side of a BD compressor system. A Filter Dryer is required in the liquid high pressure line prior to refrigerant flow control device to collect any lose materials and absorb existing moisture left after assembling of complete system. Over size filter dryers are recommended for DIY systems.
There are other 12/24 volt refrigeration similar capacity compressors to the Danfoss, Cubigel, Sikelan,Colku, Boyard, Sanheng and Retelc, although they are only used by one or two boat refrigeration companies. Should on site maintenance support  or parts be required in other world ports the Danfoss compressor is a good choice.
There are five types of refrigerant condensers in pleasure boat refrigeration when compressor size is less than 1000 Btu:
�   Static air: Older and small refrigerators use open air natural convection air over vertical wire and tube condensers. One manufacturer of an icebox conversion unit recommends that the compartment where this condensing unit is located should be at least 100 cubic feet in order to dispose of process heat efficiently. Adding a convection air fan or blower to force air to circulate over condenser coils will greatly improve condenser efficiency. For more information on performance improvements see FAN section on my web site.
�   Convection fan: For refrigeration units with capacity of less than 1000 Btu the most efficient and reliable condenser for all climate conditions is a forced air shrouded fan with a cooling fin condenser. The secrets to fan cooled condensers is their design efficiency and size. Correct installing of condenser in boat must be to insure that warmed exiting heated air is not allowed to pass through condenser again.   
�   Circulating water: Any type of a water cooling system on a small refrigeration system will compromise refrigerator reliability for a number of possible reasons. High risk exposures due to unfriendly refrigerator down time with water as a condenser cooling medium are; short life of water circulating pumps, regular water filter maintenance , marine growth build up in water piping, water flow restricted due to air bubbles entering condenser water loop. The most severe risk is catastrophic failure to refrigeration system due to low voltage discharge corrosion that occurs in water cooled condensers.
�   Submerged condenser outside hull in water:  Keel coolers or refrigerant lines in seawater outside boat where seawater medium�s temperature cannot be controlled is only going to be efficient in mild seawater temperatures. The disadvantages of these systems are problems of electrolysis corrosion and regular exterior cleaning requirements. When operated in warm seawater, compressor overheating can cause very expensive refrigerant flow problems and eventually total system failure.
�   Use of fresh water tank to dispose of process heat: Two marine refrigeration companies using small BD compressors have recommended an additional water cooled condenser circulating water by pump from fresh water tank to reduce some of the very troublesome water cooling problems. Using fresh water tank water to when air cooled condenser design fall short can result in a new set of problems.
The advantages of correctly installed air cooled condensing units are generally more reliable than any type of water cooling. Correctly installed air cooled condensing units draw air from one area and exhaust warm heated process air to another open area. If the unit you are considering is not designed to dump heated air to another area it is not going to perform well in warm climates.
There are two major disadvantages of using BD compressor, condenser, water cooled, refrigeration systems currently in use; lack of compressor metal mass cooling from normal condenser fan and loss of control module�s compressor overheat protection safety circuit. Preventing hermetic compressor overheating has always been a problem for refrigeration designs on pleasure boats. BD size compressors are fully hermetic where electric rotation field coils and armature are covered with oil making heat removal important. Most air cooled designs must rely on refrigerant flow to dispose of all process heat. It is also assumed that compressor�s external heat can be removed by moving air across it with the existing condenser fan. Attaching a small fan to compressor was tried by one system manufacturer of boat systems. Another company used a water tank attached to a � horse power water cooled system�s compressor in an attempt to reduce process heat.
The basic design practice for refrigeration system designs is to protect compressor from failure by limiting high liquid pressure and high compressor temperature. There is usually a high refrigerant pressure switch or temperature amperage overload device mounted in or on this compressor to protect it. The BD compressors rely on the electronics in control module to protect compressor from damage. If a BD variable speed compressor cooling fan amperage exceeds � amp module believes the condenser is overheating and signals the safety circuit in module to stop compressor from running. Water cooled BD compressor systems do not use the module safety circuits connected to terminals Small + and F.  This fan circuit is designed to protect against damaging high pressure/temperature by fan compressor mass metal heat reduced.
If a compressor manufacturer wanted their compressor�s to be water cooled there would be an application engineering data sheet produced by Danfoss defining water cooled operating limits.
Maintenance costs of water cooled BD compressor systems can cost as much as five times the cost of a well designed air cooled unit. Actual in service life of water cooled units is unpredictable. Maintenance of an air cooled BD compressor refrigeration unit is much the same as a home refrigerator such as cleaning dust and hair out of condenser coil inlet frequently and replacing the cooling fan in 5 to 10 years.
The evaporator in a system is where refrigerant is sprayed into a gaseous form of vapor. As the saturated mist converts to vapor it absorbs heat from evaporator plate and refrigerated space. Size, type and shape of evaporator depend on the box size that is intended to be refrigerated. Each system manufacturer provides more than one size evaporator to match each compressor�s rated Btu capacity.
�   Bare Tube Evaporator: Bare tube evaporators are not normally found in icebox conversion kits but can be used on do it yourself systems. Bare tube evaporators are sometimes used to replace a failed evaporator plate that can not be removed like one installed behind box�s liner.
�   Plate type evaporators: By attaching at least 25 feet of copper tubing coils on a metal plate is  one method used to fabricate an evaporator. As long as an  evaporator coil is in full contact with plate�s surface thermo heat transfer is more efficient than just a copper coil by itself.                             
�   Roll Bond Evaporators: Laminated metal evaporators are the most efficient and very popular with all small refrigeration companies. The roll bonding process of two or more layers of metal squeezed together under high pressure acts as a cold welding permute process. Before heavy roll bonding a special material is used on plates where refrigerant flow channels in the evaporator plate are to be formed. After bonding is complete high controlled nitrogen pressure forced between plate layers will expand refrigerant passage channels. 
�   Finned  Evaporators: are tube evaporator coils with metal fins spaced along the tubing. The surface area volume of each fin increases heat transfer from the box moving heated air closer to refrigerant. If fin type evaporators are used in a refrigerator, fin temperatures during compressor off cycles must remain above freezing. If fin coil evaporators are used at refrigerator temperature below 33 degrees F they will develop sufficient air blocking frost and become very inefficient as they are not self defrosting.
�   Eutectic Evaporators:  A eutectic evaporator plate is different from conventional plates in that by freezing a eutectic solution inside or other phase change material large amounts of energy can be stored. The larger the volume of eutectic solution the more Btu of energy can be stored inside eutectic plates. By mixing water and a type of antifreeze to establish a freeze point phase change will occur at that temperature. Different percentages of solutions can be mixed for refrigerator and freezer plates.  The ratio of frozen water to antifreeze determines the cooling effect as it melts.  When comparing different frozen solution mixes in the same volume plates Btu energy stored there is the same. A freezer plate melts twice as fast as a refrigerator plate so it needs to be twice the size of refrigerator plate. I believe that the only way to justify a holding plate on a small BD compressor refrigeration system is if there is alternative surplus energy available from solar or wind.                                 
Refrigerant Flow Control Devices
Refrigerant control devices meter flow of refrigerant between the high pressure and low pressure sides of a system. They also maintain a pressure difference to allow the high pressure fluid to flow into the low pressure evaporator where it vaporizes and absorbs unwanted heat. There are three types of flow control devices used with these small refrigerator compressors, Capillary Tube, Thermostatic Expansion Valves and Low Pressure Regulating Valves.
�   Capillary Tube Refrigerant Flow Control: With small refrigeration units having standard evaporators the capillary tube metering device with its carefully sized flow tube restriction will extend compressor life. Capillary tube refrigerant flow control prevents high pressure Btu overloads and also extreme low velocity cooling air and lubricating oil return to compressor. The length of capillary tube and its correct inside diameter will drop refrigerant pressure to maintain desired Btu cooling capacity range. The control strategy for small boat refrigeration is to keep it simple and efficient. Capillary Tube refrigerant controls are maintenance free unlike the valve controls with moving parts. For any of the refrigerant flow devices to be reliable there must be a filter or screen just prior to fluid intering the flow device orifice.  With a warm evaporator, there is fluctuating liquid and gas vapor interring Cap tube that changes mass flow as it passes through the long tube. With the variation of flow as evaporator cools refrigerant lines can vibrate and the hissing sound heard in the evaporator will change as final gas condensing to liquid occurs. The main disadvantage of a capillary tube flow control is in mobile marine refrigeration where ambient air temperatures are subject to changes that affect volume of refrigerant charge. Example correct refrigerant charge in New York�s ambient air temperatures can result in an over charge in a tropical climate like Miami. Manufacturers of ice box conversion kits service condensing unit and evaporator separately with correct refrigerant charge by weight in grams.
�   Thermostatic Expansion Valve  (TXV):  The thermostatic valve maintains a constant flow of high pressure liquid into evaporator�s much lower pressure where the refrigerant mist changes to a gas vapor absorbing heat. The TEV Flow control metering inside evaporator is regulated by a temperature sense bulb mounted outside evaporator on return refrigerant gas vapor line going to compressor.  The temperature sense bulb when warm reduces spring pressure inside TXV opening flow through evaporator. As the temp bulb cools TXV closes slowly keeping the heat absorbing process ( Super Heat) inside evaporator as much as possible. The disadvantage with TXV flow control on very small system is modification expense over a basic system without an appreciable performance improvement. The main concern with TXV used on a small compressor system is finding a valve that matches compressor Btu output without exceeding design limits of compressor. It is true that TXV valves with small refrigerant storage tank receivers used on Danfoss BD compressor eutectic holding plate systems can reduce daily energy use.
�   Low Pressure Regulating Vales: Low pressure Evaporator Pressure Regulator (EPR) controls refrigerant flow and has been used by SeaFrost for at least twenty five years successfully on small Btu compressors. The EPR valve used on SeaFrost units is installed in the high pressure line with an external evaporator pressure adjustment knob. Unlike other flow control devices that continue to lower evaporator temperature/pressures as long as compressor runs the EPR once adjusted maintains a fixed evaporator temperature/pressure. The normal design purpose for EPR valves is to control different evaporator temperatures in the same refrigerator system. A 134a refrigerator evaporator operates its best with a low pressure of 6 to 10 psi and a freezer evaporator from 3 to 6 psi. When the compressor is large enough a TXV control would be used on freezer evaporator and a EPR control used for refrigerator plate, unfortunately Danfoss BD compressors are too small for two evaporators in parallel. My dislike of using EPR valves on ice box conversion units is the refrigerant low side pressure drop in each installation is different so adjusting EPR valve sometimes takes several days to find the correct valve setting.
Suction Line Accumulator
Boat Refrigeration / Danfoss 12/24 volt control module service life
« Last post by Richard on March 04, 2018, 02:59:57 pm »
Short Module Serviceable Life can be caused by how refrigerator was installed.

Danfoss has always experienced problems with electronic control modules on BD compressors. After ten to fifteen different Danfoss module models still randomly failures occur with no warning. If we exclude lightening strikes and corrosion due to water module failures seem to be caused by voltage spikes or heat.

Voltage spikes at module are not always visible with a meter and can be present on any boat. Unstable voltage is why the module must receive power direct from battery buss using correct size wiring, fuses, circuit breaker and switches that allow no voltage drop. When compressor is correctly wired to battery buss battery will absorb voltage surges like a very large electrical capacitor reducing module electronics failures. When refrigerator is powered from a branch circuit breaker panel any item in that panel can cause a damaging voltage spike when that item is powered up or powered down. Any relay when power is turned off sends a voltage spike back towards the source. Windless, power wench, generator start relays and even cabin light relays can damage refrigerator control modules if refrigerator is wired through a circuit breaker panel instead of main buss.

Module overheating maybe the primary reason for so many electronic control module failures. Through the years Danfoss has designed static air heat sinks on modules to conduct and radiate heat away from transistors and other components inside module. Module heat increases as compressor load (amperage) increases. Danfoss�s installation application data sheets have always assumed system designers and installers would insure compressor design power amperage limits were not exceeded. What you will find in the marine industry is the elimination of module and compressor cooling air along with higher than design compressor heat loads. Only Danfoss�s AEO modules have built in module cooling fans. Danfoss�s variable speed specifications for BD50 require an additional fan for cooling control module if compressor is to be operated at maximum capacity (3500 rpm). All of the following conditions can cause module overheat failures; High condenser cooling temperatures, Repeated attempts to start do to an overloaded compressor, First box temperature pull down in a hot climate, System ambient temperatures above 105 degrees F, and too large or poorly designed holding plate evaporator coils. Failure to maintain good cool flow of condenser air, a normal maintenance item, should not be overlooked as cause of module failure.
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