12/24 Volt Boat Refrigerator’s Poor Performance Possible Causes

[Richard Kollmann]

Comparing a boat’s ice box conversion unit’s performance to a home refrigerator or even to an older boat refrigeration system is a mistake. A home refrigerator is designed around a cabinet size with each component selected to collect and dispose of a given amount of heat energy. Home refrigerators are also assembled, serviced and tested in a controlled environment your boat’s ice box conversion unit is not treated with the same quality control; this is why performance varies from one boat to another.

Small 12/24 volt ice box conversion units in the past were advertised so the consumer would believed one unit could be efficient in various size boxes. In the last 10 years when buying a 12/24 volt conversion refrigeration unit there are over one hundred options to choose from, compressor size and speed selection, evaporator size and type, and various heat removal mediums. A small conversion refrigeration unit will be efficient and perform properly only when the right unit is selected, installed correctly and the insulation is sufficient to deliver the desired box temperature in a planned geographic climate cruising area. The causes of poor refrigeration performance can usually be corrected by first identifying the deficiency and then correcting it. If a refrigeration system satisfies the desired temperature in the box its performance is good. If the daily power consumption is higher than expected, then conditions that effect short compressor run times or long run time high temperature/pressures, need to be investigated.

The most common causes of poor performance on small 12/24 volt refrigerator are:
• Poor airflow through condenser.
• Condenser fan is not shrouded.
• Heated air that passes through condenser is allowed to pass through it again. Air cooled condensing units are designed to be efficient when boat’s interior ambient air temperature is between 70 to 90 degrees F.
• On condensing units cooled by water, poor or excessive water to refrigerant heat transfer will lower overall performance.
• Compressor cycles off and on too often.
• Too much refrigerant, this is even possible on a new pre charged units.
• Small amount of refrigerant was lost on installation of line connectors or the system has a small leak.
• Thermostat incorrectly installed.
• Compressor speed too fast or too slow.
• Air or incorrect gas mixture in refrigerant.
• Very old box insulation or when insulation is wet or VIP insulation has failed. Box insulation is easily evaluated by comparing insulation exterior surface temperatures against boat interior air temperature. If insulation’s exterior surface temperature is less then five degrees cooler than boat interior air temperatures insulation is generally considered expectable.

Common misunderstandings about small 12/24 volt boat ice box conversion refrigeration units:
Most refrigeration mechanics do not know how to correctly service and make repairs do to complicated marketing design variations.
• The shorter the compressor run time the more efficient the system is, not true, on variable speed models they will run longer and are more energy efficient when running at a slower speed.
• Poor refrigeration performance is generally related to lack of insulation, not true, but high energy consumption might be linked to lack of insulation.
• A eutectic holding plate with less surface area than the recommended size of a thin plate evaporator are more efficient than thin plate evaporator is not true. Eutectic solution separation do to age is another problem with eutectic plates.
• Water cooling a small 12/24 volt unit will provide better performance than air cooling, only true in rare cases and never more reliable than air cooling.

[sailormed]

I just got my fridge back fom the fridge repair guy.
One item you did not mention:
° Wrong thermostat installed. An Italian repair shop replaced my (correctly functioning) thermostat withe a Danfoss type 3 thermostat resulting in a continuously frozen evarorator plate. Should have been a Danfoss type 1.
Is maybe not a frequent type of error

[Richard Kollmann]

Originally Posted by sailormed

I just got my fridge back fom the fridge repair guy.
One item you did not mention:
° Wrong thermostat installed. An Italian repair shop replaced my (correctly functioning) thermostat withe a Danfoss type 3 thermostat resulting in a continuously frozen evarorator plate. Should have been a Danfoss type 1.
Is maybe not a frequent type of error

Most of these small refrigerator thermostats control evaporator temperature to achieve best system energy efficiency. You may find my TECH TIP #6 helpful in selecting thermostats at:

Kollmann Marine

[OzePete]

Originally Posted by Richard Kollmann

• A eutectic holding plate with less surface area than the recommended size of a thin plate evaporator are more efficient than thin plate evaporator is not true. Eutectic solution separation do to age is another problem with eutectic plates.
• Water cooling a small 12/24 volt unit will provide better performance than air cooling, only true in rare cases and never more reliable than air cooling.

Above is wrong information..
* A correctly engineered eutectic system is considerably more efficient than a thin evaporator plate due to the eutectic system operating with a far better COP factor (Co-efficiency Of Performance.. More watts of heat removed for every watt of energy consumed) and far less inefficient start ups per day.
* We do not advocate raw water cooling of a DC refrigeration system but do promote an air cooled system with recycled fresh water back up for tropical use and / or if the unit is to be in a hot environment like the engine room etc.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[Richard Kollmann]

Right or wrong information you decide for yourself. The first law of thermodynamic energy in a refrigeration unit can be transformed from one form to another, but can be neither created or destroyed.

The energy for these small 12/24 volt refrigeration units on a boat originates from ether an engine alternator or generator or alternative electric power from wind and solar. This onboard energy produced is passed through or stored in batteries. The 12/24 volt refrigerator compressor converts electrical energy from battery into gas high mechanical pressure. The refrigeration compressor based on its design can increase input energy to a slightly higher output energy known as improving Coefficient Of Performance (COP). Entire System COP will never be greater than compressors COP. Evaporators whether thin roll bond or eutectic plates can not create more energy than the compressor produces. The best evaporator or eutectic plate’s COP that an engineer could hope for is a neutral COP energy exchange inside evaporator. Aluminum thin plate evaporators are as close to neutral COP as possible. The eutectic plates especially those with Glycol and water mixture will result in a negative System COP reduction.
Only true eutectic solution plates with brine or other corrosive solutions can match the performance of the correct size thin plate evaporator. It is true that efficiency of eutectic plates are not all the same. Plates that are designed to conduct heat directly through plate skin into refrigerant evaporator coil will react much the same as thin plate evaporators and still store energy the same as batteries. The main disadvantage of eutectic plates is there is a lack of excessive surplus energy that is not available from these small compressors without alternative electrical power from wind or solar.

[sailingunity]

Richard can you point me to which one of your books to buy? If one just wanted a manual for troubleshooting their refrigeration?

[Richard Kollmann]

Originally Posted by sailingunity

Richard can you point me to which one of your books to buy? If one just wanted a manual for troubleshooting their refrigeration?

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

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

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

[CapnSparky]

Speaking from only my experience, one of the major differences between a home refrigeration and boat system is the lack of positive air circulation throughout the box in a boat. I found a small D-cell battery operated fan that circulates the air and keeps the inside of my box all the same temperature...and I've got a BIG area to cool! It also seems to help with the overall efficiency of the system.

[Richard Kollmann]

Originally Posted by CapnSparky

Speaking from only my experience, one of the major differences between a home refrigeration and boat system is the lack of positive air circulation throughout the box in a boat. I found a small D-cell battery operated fan that circulates the air and keeps the inside of my box all the same temperature...and I've got a BIG area to cool! It also seems to help with the overall efficiency of the system.

Kollmann Marine

[sailingunity]

Thanks Richard. Yes I've found mountains of info on your website however I like to have paper references when possible, in case I can't get online for some reason. I've got a small leak in my system and while topping it up left the gauge set on (I have holding plates) to watch the pressure, well obviously I have a leak in my gauge set as well as when I came back it was pulling a vacuum. I added some freon back in to the appropriate pressure, however it went into cycling mode so often it couldn't keep the box warm. Did the LED trick, 3 flashes. So I borrowed a nice gauge set and vacuum pump from a friend and vacuumed it down and refilled it. I kept adding freon until both plates were frosted over. Things working great, shut the system down, came back months later, and it was so overcharged the compressor wouldn't start. After reducing the charge some I can get it to come on and stay on but it will only frost over 1 plate, the other gets cool to the touch but never frosts over, adding more freon only seems to reduce performance (the box starts to warm up). Its an EZ Cold system from 2008 which has had the water cooling portion removed (PO had major issues and removed it).

Contemplating just taking the whole thing out and replacing with a evaporator plate system, but reading your comments on how durable the danfoss compressors are I really want to try to make this work.

[Richard Kollmann]

Originally Posted by sailingunity

Thanks Richard. Yes I've found mountains of info on your website however I like to have paper references when possible, in case I can't get online for some reason. I've got a small leak in my system and while topping it up left the gauge set on (I have holding plates) to watch the pressure, well obviously I have a leak in my gauge set as well as when I came back it was pulling a vacuum. I added some freon back in to the appropriate pressure, however it went into cycling mode so often it couldn't keep the box warm. Did the LED trick, 3 flashes. So I borrowed a nice gauge set and vacuum pump from a friend and vacuumed it down and refilled it. I kept adding freon until both plates were frosted over. Things working great, shut the system down, came back months later, and it was so overcharged the compressor wouldn't start. After reducing the charge some I can get it to come on and stay on but it will only frost over 1 plate, the other gets cool to the touch but never frosts over, adding more freon only seems to reduce performance (the box starts to warm up). Its an EZ Cold system from 2008 which has had the water cooling portion removed (PO had major issues and removed it).

Contemplating just taking the whole thing out and replacing with a evaporator plate system, but reading your comments on how durable the danfoss compressors are I really want to try to make this work.

Adding refrigerant will overload compressor on that two plate system. The solution is to extend refrigerant > normally supper heat into second plate without increasing compressor amperage. I normally suggest this simple test first before making an adjustment to the expansion valve. Remove clamp holding valves temp sensing bulb to return refrigerant line. Now rap electrical tape around refrigerant tube so bulb will be insulted away from line somewhat. and reinstall clamp. Run compressor for several hours and email me. Important stop this test if frost extends beyond second plate towards compressor.

[sailingunity]

And what happens if frost extends beyond the second plate? I only ask because the very first time I added refrigerant (before it started cycling so much) I did get that condition, didn't realize at the time it was bad.

[getyourbone]

The reason for my fridge/freezer not cooling effectively on the boat was too light duty of wiring installed when run from the battery. Even though it was within amperage specs for 12 V, as soon as I increased the gauge it worked perfect.

[Richard Kollmann]

Originally Posted by sailingunity

And what happens if frost extends beyond the second plate? I only ask because the very first time I added refrigerant (before it started cycling so much) I did get that condition, didn't realize at the time it was bad.

Adding too much refrigerant will always increase load on compressor. If too much refrigerant is added the high amperage load on compressor will stop compressor.
The EZKoll two plate system's refrigerant flow are normally controlled by an expansion valve. Did you locate this valve? If you can not find this valve your problem is going to be a little more difficult to solve.

[ayates]

FYI... The attached images show some real life performance data from a refrigerator/freezer. The unit was a well insulated (except for the door) Nova Kool RFU-9000.




Allan.