Nine Different Ways to Improve 12 volt Refrigerator Performance with Fans

 It is difficult to design refrigeration for mobile applications like boats and RVs. What works in an RV may not work in a boat. RV’s have front door openings and exterior air vents for condenser and compressor heat disposal while boats usually have top loading hatches and no interior vents. Also freezing-chamber evaporators can not always be located above refrigerator areas. There are a number of ways to improve and expand a mobile refrigerator’s efficiency by adding circulating or heat disposal fans such as the following installation applications:

 

Index of Improvements with Fans

1. Adding an Extra Fan with a snap action thermostat that is not controlled by the compressor’s electronic module.

2. Spillover Fan and its Thermostat creating two temperature zones like refrigerator and freezer.

3. Spillover thermodynamic simple principals

4. Simple spillover fan system.

  5. Planning a Spillover System

  6. Air Tumbling Fan

  7. Condenser Cooling and process heat disposal Fan or fans.

  8. Condenser Fan CFM and Amperage

  9. Condenser Fans

 10. Electronic control module Cooling Fan

  11. Compressor cooling Fan

  

1. Adding an Extra Fan with a snap action thermostat

That is not controlled by the compressor’s electronic module

         Normal heat removal from a refrigerator’s condenser, or electronics and even the compressor itself may not be as efficient as it should be. So how can a fan be added to move this unwanted heat away?
         To control the exhaust fan or add a condenser fan I have used a snap action fan control thermostat switches available from www Granger at a cost of $12. A fan should only be operated as needed. Their p/n is 2E245 they close at 110˚F and open contacts below 90˚F. When attached to a line from the compressor or warmest spot on refrigerator’s condenser with plastic tie wraps the fan will run when the compressor heats the outlet tubing or condenser coil above 110˚F and shuts off the fan when temperature switch drops to 90˚. Power wire for this fan circuit must be fused to the correct size. This snap action switch is good for 10 amps at 12 or 110 volts. See Granger catalog
.

 2. Spillover Fan and its Thermostat creating two temperature zones like refrigerator and freezer.

For a spillover box to have two efficient temperature areas there needs to be at least a 25˚F temperature difference (Delta T) from one side of the divider to the other. A spillover divider should have at least an insulating R value of 10.

A small fan located midway up on the divider along with an equal size return hole at top of divider will provide circulation between sections. The main thermostat controls the freezer average temperature by monitoring the evaporator temperature. The divider fan controlling refrigerator temperature will be controlled by a separate thermostat with its temperature probe located in refrigerator section.

For reasons of energy efficiency small refrigeration units use a thermostat that is calibrated for evaporator temperature instead of box temperature. When selecting a thermostat for controlling a divider fan, it must have its range control from 20 to 40˚F. In some cases these zone control thermostats are identified as Cooler box thermostats or the more expensive units are called Temperature controllers and they range from -20 to +40˚ F.

Divider fans must be small for two reasons since too much air movement when the fan is running will raise freezer temperature and when the fan is not running, a large fan opening may change the Delta T between box areas. I have used a number of the one inch square ½ inch thick 12 volt Radio Shack Fans. Tey seem to last on live aboard boats 4 to 5 years even at low temperatures. Years ago I used the 3 1/8 inch muffin fans that move 25 CFM but they were too large. This is the information on divider fan I recommend now selling for $12.

12vdc (rated voltage)
10.8-13.2vdc (voltage range)
6500 rpm +/-10%
.13a max @12vdc (rated current)
1.56 watts max @ 12vdc (rated power)
7.7 cfm +/- 10%Q
29db +/- 2db

The wiring for this divider fan would require a 1 amp fuse, an Off-On switch, and zone temperature thermostat. Since the fan is operated by transistors correct wire polarity is important. Because this divider fan is a separate system from the refrigeration unit, it must operate when the refrigeration unit is cycled off so it will not be connected to the BD compressor’s fan circuit. Twin red and black wires of 20 gauge or larger is OK for a fan as long as a one amp fuse is installed at the power source. Fan power must be available anytime the refrigerator box is intended to be kept cold.

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 3. Spillover thermodynamic simple principals

 

Very few boat icebox conversion Spillover refrigerators function properly because basic thermodynamic, simple principals are ignored. A separating divider between a refrigerator and a high temperature freezer of +15 to +22˚F needs an insulating value of at least R5. Two inches of extruded polystyrene with impact resistant material on each side will provide a temperature difference between separated areas of 20˚F. To extend the flavor quality of food stored for more than three weeks the freezer temperature range should be zero to +15˚F. Then the divider will need to be insulated to R10 to R15. In assembling a spillover system or any refrigerator or freezer think about incorporating these principals so they work for you instead of against you.

In a static state, air is a bad conductor of heat. When air is trapped and can’t move, it becomes a good insulator. Heat conduction occurs when two objects at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature. For air to be a good conductor of heat, there must be movement and collision of its molecules, therefore there must be air movement inside the box at all times.

The warmer the air is the less dense it is. So it tends to rise and cooler more dense air sinks. Before home refrigerators were redesigned with fan cooled evaporators, boxes were equipped with wire shelving allowing heated air to move naturally and slowly tumbling in the box. With an evaporator at the very top of the box, air below it tends not to stratify in layers. Warm air on top and when cooled it drops.

Cooling is the process of removing heat so heat removal inside an area depends on a heat conducting medium (air) being able to surround warmer items as much as possible and then return to the evaporator where the heat is absorbed.

My recommendation for a spillover refrigerator is this. Most boat spillover boxes are side by side requiring pressurized air movement to maintain individual box temperature control. One thermostat controls freezer temperature by cycling compressor on and off. A second thermostat controls a very small refrigerator fan located in middle of divider. Return air to freezer is provided by a hole at top of the divider. Install rails across the bottom of the box and up both sides to insure that the lower product stays frozen.

The compressor must have capacity to handle planned worst case cruising climate. The Evaporator should be installed in the freezer covering as much wall space as possible and have equal maximum capacity of the compressor.

The following are Q&A’s that I have received on the above subject.

My refrigerator cabinet is divided in half. Half for the freezer side and half for the frig side. I am looking for a thermostat control that will turn on the small computer fan that pulls air in from the freezer side to cool the frig side as it is needed. Do you know where I can find one? The one I had was a simple little mechanical deal that fit right in the frig?

ANSWER: I don’t know of an inexpensive fan control thermostat. The one I sold is no longer available. Adler Barbour does sell one but he problem is that the desirable temperature range for these thermostats is 25 to 40˚ F. I have used a temperature controller for this fan although it’s a little pricey at $60. With a temp range from -25 to +40˚ it gives good control and has a differential adjustment. It can be mounted outside the box as it has a 60 inch remote bulb. These controllers are available from several manufactures Ranco's P/N is 010 1408 or equivalent.

     Question: Spillover performance: I recently bought a sailboat with the intention of a world Pacific (Bora-Bora) cruise three years from now. The boat came equipped with a Danfoss BD35 with keel, water cooled. It has an evaporator in an L shape of 30'' long that turns 90˚ and prolong 12'' more for a total length of 42''.The evaporator is 12'' high. The box is 9 cubic feet and includes a 2'' divider in the middle 2'' in height smaller so the air could flow from one compartment to the other. My question is: Does this set up act as a freezer on one side and refrigerator on the other side or is it only a large reefer? Should I modify it to have 1/3 freezer and the rest fridge by moving the separator towards the evaporator? How close should the food be from the evaporator to have a good heat transfer and stay frozen. Would it be a good idea? Is it better to change the evaporator for a square one instead of an L shape one? I have a 1200Amps battery bank, a wind generator, a 110Amps alternator and am thinking about solar panels.

Question: The box is urethane sprayed 5'' insulated factory made. I intend to add a 1'' polyurethane panel (instead of Styrofoam) wrapped in plastic and a 1'' bubble heat shield. How does it sound?

ANSWER: Your BD35 compressor and L shaped evaporator with keel cooler will do a reasonable job in seawater temperatures of 65 to 75˚F. A nine cu ft combination spillover box is too large for the small BD35 compressor when cruising in tropical waters. Spillover icebox conversions generally provide only short term frozen food storage. The closer the frozen product is to the evaporator the longer it will maintain its quality.

Adding insulation to the outside of the box will not improve energy performance but adding extruded polystyrene (Moisture Resistant) insulation to the box’s interior will, but it also makes box smaller.

If I were you I would use the present box as a refrigerator cooler and buy a stand alone portable freezer like the ENGEL 45

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 4. Simple spillover fan system.

Electrical

Fused red power wire to single pull single through a simple Off On         switch.

Red wire from other side of switch to thermostat.

Red wire from other side of thermostat to red wire of fan.

Black wire of fan to a ground.

An area control thermostat is used instead of a refrigerator evaporator thermostat in order to control refrigerator areas air temperature in a suitable range 33 to 45˚F.

Best installation of a spillover fan is to recess it inside one inch thick or thicker divider, mounted in a one inch hole or mounted on the refrigerator side of the hole. The Fan is located midway up divider and removes air from the freezer pressurizing the refrigerator at less than 10 CFM. Return air to the freezer is by a one square inch opening at the top of the divider.

 5. Planning a Spillover System

 We are looking at replacing the current system with a new AB Cold Machine CU 100 and the 100 series evaporator plate rated for 15 cu ft. The boxes are SS. The freezer section is 3.3 cu ft, the divider is 2" thick with holes at the top and bottom for spillover. There is no fan currently installed. Fridge is 6.3 cu ft. Insulation is 3~4 inches.
The questions are?
        
Can the system described above work as a spill over system? Should the bottom hole be plugged and a duct be fabricated so the fan pulls air from the center of the freezer to pressurize the fridge side? Would it be better to use two smaller systems and run them independently?
Thanks!

ANSWER: Without knowing your planned cruising area I can not verify if capacity of BD50 or an evaporator could handle a 3.3 cu ft freezer and a 6.3 cu ft refrigerator. The BD50 compressor powered, condensing unit will be large enough for a 9.6 combination box when cruising the West coast of US or cruising in north on the East coast. You need to watch the slide show on my web site for equipment selection and a boat’s DC power grid requirements. Above Latitude 36 N the daily amp-hrs consumed would be maybe 70 daily. Cruising in the tropics daily amp-hrs may reach 150.

Adler Barbour has changed hands five times and now is lumped into Demitic’s inventory so I would need evaporator description as Series 100 does not identify your planned unit. For a freezer to function properly the evaporator needs to be in the freezer surrounding the frozen product as much as possible.

If the spillover divider plan is to be without a fan, all holes presently there should be plugged and later opened only enough to allow natural air movement to achieve the temperature separation you desire. My recommendation would be to plug all holes in the divider except for a one inch hole at the top of the divider. Then install a 1/10 amp one inch square fan mid way up from box bottom in divider. The fan should be controlled by a separate special zone thermostat (cooler type thermostat) sensing refrigerator zone temperature.

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6. Air Tumbling Fan

 

Conventional home chest freezers use wire baskets to allow natural air circulation throughout a box. Home refrigerators are designed to assist in air tumbling circulation by having some type of open shelving when the evaporator is located at the top of the box. The evaporator absorbs heat from the air then cool air descends absorbing more heat and rises back to the evaporator.

A circulating fan in a refrigerator or freezer will not produce good results in a box without open shelving unless a series of standoff rails are placed on the walls and floor to provide a space for air circulation.

Top opening refrigerators and freezers on boats have poor air flow and therefore the temperatures will vary from side to side and top to bottom. Without air movement in a refrigerator or freezer, temperatures tend to stratify in layers. Most commercial and home refrigerators are constructed to allow the natural movement of warm air rising and cold air descending across the evaporator to tumble the air. The addition of a small fan can help most refrigerated boxes. I recommend a one inch square muffin fan that runs at all times when the refrigeration is in use. I ran over two hundred tests to prove what works and what does not. Many are in my 12/24 volt manual.

TUMBLING AIR FAN TEST:

The thermostat was locked and outside air temperature maintained between 79 to 82˚F. for these 24 hour tests. In test 119 the food product blocks the transfer of heat. In test 120 the small airflow from a one-inch muffin fan tumbling box air, lowered temperature eight degrees at the far end of the box. This fan also increased the efficiency of the evaporator and increased Btu output from the compressor.

 

Question: What about flashlight battery powered fan sold at West Marine?

ANSWER: These battery fans do work and I have tested the Fridge-Mat unit. It does run 30 days on one D cell battery. These units were designed for the open shelving RV refrigerators to assist the natural tumbling of the air in a box. I have no idea how many months they will last as the motor looks like it is out of a toy.

Boater REPLY: I had one for four years and it worked all season(six months, only on weekends) on two D cell batteries. I would still be using it but I dropped it and broke it. I thought it made a big difference, enough so that I bought another one (wal-mart less then $20) they help to avoid "warm" spots in the cooler and help to cool everything evenly.

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 7. Condenser Cooling and process heat disposal Fan or fans.

Performance and energy efficiency of any refrigeration unit depends on the condenser’s Cooling Medium temperature. Refrigerators are generally designed for optimum standard day air temperature of 68 to 70˚F. Most small 12 volt boat refrigeration units have long capillary tube, refrigerant expansion devices that control refrigerant at a specific volume of refrigerant flow. If the condenser’s cooling medium varies above or below the manufacturer’s design temperature, a system’s optimum performance will change. The reason performance changes when the cooling medium temperature changes is that the refrigerant’s high pressure increases and as temperature increases it draws more current.

Home condenser cooling medium temperature do not change much inside a home where creature comfort is maintained but when installed in a boat ambient air temperatures do change.

 The key to gaining the best performance from small 12/24 volt refrigerators or icebox conversion units is how correctly it is installed in your boat. Using cabin air directly into intake side of condenser cooling coil and using a fan to dispose of process heated air to an open area so that it can not re-circulate again is what I mean by correct installation. Some manufacturers elect not to use positive displacement fan shrouds to insure all fan air capacity flows through the condenser coil. These units should be avoided if they are to be installed in a closed space. If you want peak performance on an already installed unit, look at ways to better direct air over the condenser coil. Standard designs for condenser fan capacity on condensing units powered by Danfoss BD compressors are to use four inch muffin fans with a cfm capacity of around 60 cfm.

Twelve condenser fans are also available in 80, 100, and 130 cfm. The problems with replacing a small capacity fan with a larger capacity one is that they are noisier and higher cfm fans are 5/8 inch thicker than the original. The larger 100 and 130 cfm fans can be connected to Danfoss BD2.5 and BD 3 modules direct because they draw less than one amp. If a fan draws more than ½ amp it cannot be powered from the BD35 or BD50 compressor modules direct and a relay is required. For tropical climates, my designed units all had 80 cfm fans. The best thing about these little air cooled units is high refrigerant pressure performance can be maintained in cool climates by blocking a portion of condenser coil. Danfoss BD35 and BD50 compressor module condenser fans are always 12 volt even when module and compressor are running on 24 volts.

Seawater Temperature Affect On Boat Refrigeration

 QUESTION. In your 12/24 volt manual section on selecting a refrigeration unit you separate the units by what works in cold climates but will not work in warm climates. On the Great Lakes we have 90° days the same as they do in the tropics what’s the difference?

ANSWER: The seawater’s temperature surrounding the boat’s hull has a major effect on the ambient air temperature inside the boat and plays an important role in the performance of a refrigeration system. Cruising area seawater temperatures are not listed as part of a refrigeration sales brochure but should be. Water temperature also must be considered if the refrigeration equipment selected is to be water cooled. Failure to consider the effects of different seawater temperatures when selecting a boat refrigeration system is why many refrigerators perform poorly.

Good boating weather is when the temperatures are in the 70° to 90° F. range. In this country when there are good boating temperatures the water temperatures can vary in the north from 50° to 98° F. in south Florida the Bahamas and the Caribbean. When you think of California having good boating weather we forget the Pacific ocean is cold. Example, weather Station 46025 - Santa Monica Basin in August reported a seawater temp of 69° while Station FWYF1 - Fowey Rocks, FL the same day reported 86.7° F.

Ambient air and seawater temperature along with the box’s insulation and intended use, will determine the size and type refrigeration system for a particular boat. There are formulas for calculating the Btus of heat effect on large walk-in refrigerators that some think can be scaled down and used to project a small boat refrigerators total heat load. I believe the estimated heat load should be based on worst case conditions such as: Thermostat set to maintain 33° in the coldest part of the refrigerator box, normal daily product flow in and out of the box, number of people on board, ambient temperature of 90° F. and seawater temperature of 86° F. If the box has a front opening door add infiltration heat loss. Using the method in my book for a six cu. ft. refrigerator box in worst case conditions, with three inches of good foam insulation, four people on board and a 14 inch front opening door, the heat load would equal 6440 Btu per day. If the boat were in Santa Monica CA. instead of in the tropics where the seawater was 17 ° cooler there would be a 20% to 30% reduction in the daily heat load projection. In this same comparison if the condenser were water cooled a 34% reduction in required daily Btus are possible. The problem with seawater cooled condensing units is they begin to loss efficiency when the water temperature drops. If the same water cooled unit that was designed for the tropical conditions above were operated the same day on a boat at Station 46026 - SAN FRANCISCO with a water temp of 54.5° its performance will be less than good. When selecting a refrigeration unit you want to error on the cool climate side not the hot climate side.

On pleasure boats when the refrigeration compressors are larger than 1/6 Hour power the process heat is almost always removed by seawater. Maintaining a reasonable temperature range of the condenser cooling medium, air or water is important, too low or too high a temperature will affect the system’s performance. Large commercial water cooled refrigeration units have water flow regulators to maintain the high side pressure in a system, but they are not available on the small systems. Two of the pioneers in pleasure boat water cooled engine driven refrigeration, Crosby and Grunert, used manual seawater bypass valves to keep the high pressure refrigerant in the proper range. With an adjustable water bypass the same system can operate efficiently in the Pacific or the Caribbean. It seams like refrigeration systems manufacturers located in cooler water climates tend to error more when it comes to adequate seawater cooling for use in the tropics. The small refrigeration compressors with capillary tube expansion devices are very sensitive to temperature variations in the cooling medium, therefore, water cooling is a poor choice unless operated in 55° to 75° F. waters. Small air cooled condensing units are much more suited to varying air temperatures. Adler Barbour and Technautics are two of the companies that design with adequate air cooling for the tropics and if the same units are operated in a very cold climate the airflow across the condenser can be restricted or a portion of the air recycled.

 QUESTION: Last fall I added an additional vent and muffin fan to help cool the enclosure of my 8 cu ft. marine fridge. I have the fridge out and am trying to decide if I need to change where the fan is, direction etc. The compressor and condenser are located at the lower rear of the unit in a cutout across the back and the fan on the condenser sucks air from left to right - looking at unit from the front. Air goes thru the condenser then over the compressor and then the electronic unit for the compressor.
As luck would have it all vents are on the right side of the enclosure toward therear; two near bottom ( lowest one has my added fan ) and one up high.
With the unit installed, there is about 4 inches of air space on sides and back.
I think some type of cross ventilation across the lower back of the unit would be best but that is not possible on my boat.
        
My question concerns the aux fan. Right now it blows in on the lower vent and I am wondering if that fights the airflow going in the other direction from the condenser fan. Should I reverse it to pull air from the lower vent? Or should I be pulling air with the fan on the upper vent. Not really sure what is best?

 ANSWER: Because I can not look at the physical configuration of your refrigerator’s heat removal system, I can not provide detailed help in improving performance. Refrigerators sold for RV applications and sometimes used in boats will have problems in warm weather disposing of their process heat. The only way to cool an area is to remove the heat in that area and send it somewhere else. The compressor pumps refrigerant through the system which picks up heat that must be disposed of by a condenser coil.

Many refrigerators have large vertical static air condenser coils mounted on rear of the cabinet to dissipate heat to outside air by natural air movement. Natural movement of air on this type unit is IN at the bottom and exiting warm air OUT at the top. If a refrigerator is to be built into a cabinet the exiting air chimney size is listed in the installation instructions, Example, Norcold lists 100 sq. inches.

On refrigerators where the condenser is cooled by forced air from a fan, air must be guided from an area containing air with low ambient air temperature into the shroud of the fan. The shroud insures that all of the fan’s air passes through the condenser coil by pressurizing the area between the fan and coil. After heated air leaves the condenser it is still under a small amount of pressure and must be guided by baffles to an exit point that prevents it from re-circulating back to the condenser fan a second time.

Additional heat removal fans are sometimes required to assist in process heat removal to another area but they are of no use if they only circulate air in the same warm compartment.

 QUESTION:  increasing condenser fan capacity

 Thanks for all the help you gave via e-mail, both BD 35 units are running well, fully frosted evap plates, with nominal temp lines to and fro the compressor.
         I have received a pair of fans with 108 CFM airflow to replace the supplied units at 89CFM, but even though the new fans are spec 50ma, neither will run more than a few seconds before shutting off. Supplied fans are spec 37ma. Perhaps start up current is exceeding allowable current.
Two flash code is displayed on one unit, but the other unit seems to have a faulty LED which I'll have to test and replace.
Kind of odd, but both units are behaving identically.
The LED gets positive from the power SW, so the Neg leg must be controlling the flash patterns when present.
         A relay is no problem, but I'm thinking that I'll direct wire the Condenser fan to the power SW, and add fans on the Current limited circuit aimed at the control unit fins.
         What do you think? This would avoid a relay and provide extra cooling.
         Also, how should an LED be wired to cycle with the Compressor? Via the Fan limited current circuit? Both Compressors mask each other noise wise, so led's to indicate cycling would be good. What resistor value would be used on these LED's?
Thanks again,
Chris

ANSWER: There are two terminals on Danfoss’s variable speed control modules designed to operate cooling fans that draw less than ½ amp, these terminals are the small + and F. Presently on your BD35 modules the red + wire from fan is connected to the modules small + terminal not large + terminal and black fan wire is connected to F ground terminal. This small + and F electrical circuit is energized when compressor is running. Should fan begin to show signs of failure by drawing more than ½ amp electronic control module will stop compressor. When brushless (muffin) fan’s load is less than 80 CFM normally it will be less than ½ amp. If your plan is to add additional load to this fan circuit then another source of 12 volt power can be provided by a relay.

Adler Barbour’s CU models already have a relay for add-on 12 volt accessories. Other manufacturers use an inexpensive Auto relay pictured on page 43 of my 12/24 volt refrigeration manual. Last time I was at Pep Boys this relay was under $3. Electrical drawing above relay on page 43 is for fixed speed compressor modules. All of these inexpensive automobile relays have two coil terminals 85 and 86 and two or three load transfer spade terminals Fused power source is connected to terminal 30 and Fan load (red wire) to terminal 87. If relay has a fifth terminal 87A it is normally closed and not used. All Danfoss BD compressor systems use this type relay on water pumping condenser systems.

Refrigerator run LED you want would also be connected to same terminals as fan. As far as 12 volt LED resistor I would recommend one already designed with resister built in like Radio Shack P/N 276-270A, but Green colored. I have used a 370 ohm resistor on plain LEDs before but wattages are not the same on all LEDs. If you use a plain LED you need to get its polarity correct. If LED is for the troubleshooting circuit its current must bi 20ma or less.

 Condenser Fan AC/DC 101N500 Module

QUESTION: The compressor and fan would run fine on 120VAC but on 12VDC the compressor would bump during which time it almost sounded like an old style analog modem with sound coming from the control board. The fan would turn on and then both would shut off. The LED I had installed would present a 2 flash code, fan over current. We rechecked the 12VDC wiring and all was in good shape (less then 10 ft run of #6AWG to fully charged 440ah house bank battery's) I removed the control module and cleaned all the terminals with no luck. I then replaced the fan with a lower amp draw fan and it seems to have fixed the issue. Do you know if the fan is a common problem with these units? This is an Nova Kool RFU8220 model.
Sean

 ANSWER: Module, small Plus + and F terminals, for fans are limited to 1/2 amp and 12 volts. When an electrical load on these terminals exceeds 1/2 amp, the module will assume the compressor may be over heated and will stop the compressor. If the fan motor bearings are dry and about to fail or any one of its many internal transistors is week, amperage will exceed 1/2 amp and willstop the compressor. Life expectancy of Muffin brushless fans with ball-bearings instead of bushings in a live aboard boat last from five to seven years.

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 8. Condenser Fan CFM and Amperage

 Replacement 12 volt 4.68 inch muffin fans are available in several CFM ratings from 35 to 100 CFM. And draw from .35 to .50 amps. If cruising in the tropics, the 80 to 100 CFM fans are the most efficient but as the CFM is increased the noise level is also increased. These are very common fans and can be found at most electronic stores. Www.mouser.com phone 800 346-6873 has the ball bearing replacement fan for $13. WWW.Rparts.com also sells replacement fans rated at 60 cfm and 95 cfm their cost is $40.

A condenser fan is replaced by removing the four sheet metal screws on the fan corners. Then disconnect the small red and black wires from the unit’s electronic control panel or terminal strip on some models. Be sure to remember which terminals are red and black. If you purchase the higher output fan it may be one inch thicker so longer number 8 screws will be needed for the replacement. It is also possible on some manufacturer’s fans that the mounting holes may need to be drilled to accommodate the number 8 screws. The most difficult condenser fan to remove is on Adler Barbour CU 100 and CU200 condensing units as the fan is located inside the shroud. On CU units remove the pop rivets holding the shroud to coil. Next disconnect fan wires and remove screws inside shroud to get fan out. Because the space on Adler Barbour’s CU models is so tight only the one inch thick fans with lower cfm will fit as a replacement.

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 9. Condenser Fans

QUESTION What about a fan to improve evaporator capacity when evaporator is too small for compressor’s Btu Output?

ANSWER: It does not make any difference whether the refrigerant flow is provided by 12 volt or 110 volt energy if the output energy is greater than the capacity of the evaporator or holding plate. Repeated compressor cycling before desired box temperature is achieved can indicate surface area heat conduction of evaporator or plate is insufficient and adding a fan that causes convection heat transfer can improve overall system efficiency.

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10. Electronic control module Cooling Fan

 Module overheating may be 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 the 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 the control module if the compressor is to be operated at maximum capacity (3500 rpm). This fan is in addition to the condenser fan air. All of the following conditions can cause module overheat failures; High condenser cooling temperatures; Repeated attempts to start due to an overloaded compressor; First box temperature pull down in a hot climate; System ambient temperatures above 105˚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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11. Compressor cooling Fan

All electric hermetically sealed compressors rely on cool return refrigerant gas for cooling of the compressor. When the compressor is exposed to maximum heat loading, the condensing unit’s fan airflow provides additional cooling for the compressor. On water cooled refrigeration, the manufacturers have added water cooling jackets clamped to the compressor or fined heat sinks in an attempt to cool compressors. On unfriendly water cooled systems like the ones using 12/24 volt Danfoss BD compressors I have always recommended adding a compressor cooling fan. If BD compressor is allowed to run hot so will its control module run hot causing it to fail.

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