Refrigeration is a complex balancing act. If one part of the system changes, the other parts will react accordingly as the system seeks balance. Systems can still function to some degree even if they aren’t working properly, however they may consume much more energy than they should.
Some refrigeration problems are simple, and others are more complex. We are happy to offer some basic troubleshooting to help you understand why your refrigeration system may not be working properly.
The chart below is for a conversion kit or self contained fridge that uses the very common 12V Danfoss compressor (BD-35, BD-50 or BD-80). Please feel free to use this flow chart to help narrow down what the problem may be.
Have you used the flow chart above, but found that it doesn't relate to your problem?
Here are some additional potential problems and their potential causes:
Problem: The refrigerator is running (maybe constantly), but not cooling very well and unable to maintain temps consistently. (Assuming your compressor is running and your evaporator is fully frosted).
- Bad door gaskets or seals. A badly sealing door can cause your fridge to run almost all of the time to try and remove all of the heat that is infiltrating. Use a dollar bill and close your fridge door on it. You should not be able to easily pull the dollar out. Try this all around the perimeter of the door. If it slides up and down the gasket easily and can be pulled out without the gasket grabbing it, then you may need to adjust your door catch (there is usually an adjustment screw under the door catch that allows you to slide it in or out) or the door hinges (if possible). Otherwise you may need to replace the gaskets, especially if you can see any gaps or holes in the gasket. A 1/8" gap that is 8" long is equal to a one square inch hole in your fridge.
- High ambient temperatures. Is it pushing 95-100 degrees in your galley? If so, there just may be too much heat entering the refrigerator or freezer box for the system to remove. This will be completely dependent on the amount of insulation your box has, as well as the condition of your door gaskets. At those ambient temps you should expect your fridge to run almost constantly. If your compressor is in a very hot engine room it will also cause your fridge to run longer as it is more difficult for the condenser to reject the heat that it has picked up from the fridge box.
- Restricted airflow at the condenser or poor water flow through a water condenser. If the condenser can't reject the heat it's picked up in the fridge, that heat will then be recycled back into the fridge, making it almost impossible to cool properly. Airflow could be restricted due to a number of things. Dirt and dust clogging the condenser coils and fins (either vacuum the coils or use compressed air to blow them out). A physical blockage like a bag or other cargo has been pushed against the fan, preventing air flow. The condenser fan itself may have failed. If its water cooled, check operation of the pump and the volume of water flowing out of the discharge port to make sure it's adequate.
- Evaporator is covered in a thick layer of ice. Believe it or not, ice is a great insulator. When there is a thick buildup of ice on your evaporator the heat from your fridge can't be removed very quickly. That means the heat from the ambient environment around the box is able to heat the box faster than the ice covered evaporator can remove it, causing your fridge to run constantly as your box temperature slowly rises. It is very important to keep your evaporator ice free for most efficient performance. A thin layer of frost is completely normal, but if your evaporator looks like an iceberg its time to defrost! Where does the ice come from? It comes from moisture in the ambient air that enters the fridge every time you open the door, from uncovered food items (such as produce) and from air infiltration through gaps in the gaskets and door seals. Keep in mind that the air pressure in a 35 degree box is lower than the air pressure in a 70 degree galley, so that warm moist air is actually pushing itself into your fridge. If you have a front load fridge every time you open the door all that cold air falls right out at your feet, and the warm moist air is sucked into the top of the opening as that happens. Top load freezers and fridges don't have that same problem. If you find yourself defrosting more often than every few weeks, check your door gaskets! Remember, never use metal scrapers or tools to remove ice, you could seriously damage your evaporator.
- Too much warm product added to the refrigerator or freezer. Your compressor can only remove a set number of BTU's per hour, and almost half of that capacity is needed to simply maintain the box temperature (depending on ambient temperature, box insulation, size of evaporator, etc). A BTU is the amount of energy it takes to raise or lower a pound (which is about equal to a pint) of water one degree Fahrenheit. So it takes 8.3 BTU's to lower one gallon of water one degree. For example, if you add one gallon of 80 degree water to your 35 degree fridge, that is a temperature difference of 45 degrees. 45 degrees x 8.3 BTU's = 374 BTU's that need to be removed just to cool that one gallon of water (or soda or beer) down to 35 degrees. A Danfoss BD-35 compressor (the marine refrigeration industry standard along with the larger BD-50) at high speed can remove 248 BTU's per hour (at 90 degree ambient temps and with a 0 degree evaporator temp, common in fridges). That means it would take 1.5 hours to cool that gallon of water if it didn't have to keep the box cool at the same time. Remember half of the capacity is required to keep the box cool, so in reality it would take 3 hours to maintain the box temp as well as cool your gallon of liquid to 35 degrees. That means you should expect your fridge to run constantly for about 3 hours before it shuts off after adding one gallon of 80 degree liquid. This is the reality of boat refrigeration, and all manufacturers of boat refrigerators face the same challenge. It is all about a balance of refrigeration capacity and amp draw. In a 120V household refrigerator there is an unlimited amount of electricity available, so inefficient oversized compressors that can handle occasional large cooling loads can be installed without concern. On a boat, every amp hour counts, so the refrigeration design is all about high efficiency with minimum power consumption. The best approach is to install the largest evaporator possible (ideally with a fan) to absorb the heat quickly and a large condenser (in a cool environment) to reject the heat quickly. So what's the lesson here? For best performance and efficiency, try to add precooled product to your fridge, not warm!
Problem: Compressor shuts off then immediately tries to restart again. This may happen just once, or it may start and stop many times before it starts up or shuts off. This may be a constant or intermittant problem.
- Mechanical thermostat is worn out. Most standard thermostats are mechanical and after 7-10 years of service inside of a fridge or freezer it's not uncommon for corrosion to build up on the electrical contacts. The Danfoss motor controller only sends out 5 volts DC to the thermostat, which isn't a lot of electrical "push", meaning a small amount of corrosion or buildup to the electrical contacts can prevent a consistant electrical connection back to the motor controller. This results in the rapid cycling of the compressor. The solution is to replace the thermostat, Contact us for a replacement part.
Problem: Sweating on the face of the fridge, usually between the freezer and fridge doors. Sweating occurs when the surface of the fridge face is colder than the dew point of the air, the same way a glass of ice water will sweat on the outside. The dew point is dependent on the temperature and relative humidity of the air.
- Door Gaskets are leaking. This causes cold freezer air to drop across the face, lowering its temperature below the dew point of the air. Test your gasket seal using the dollar bill method outlined above.
- High humidity in the boat. As we all know, marine environments are humid. If you have high humidity in your boat, this can cause excessive sweating, as well as quick ice buildup on the evaporator. Keep a dehumidifier running on the boat when its sitting at the dock.
- Freezer temperature is too cold. If you keep your freezer super cold (0-5 degrees) that may lower the temperature of the face of the fridge below the dew point of the air. Raise the freezer temp to 10-15 degrees, which will also lower power consumption (by as much as 25%!) and improve efficiency.
Problem: Water pump is not pumping enough or any water through water cooled condenser. This can cause very high head pressure, potential compressor damage and poor refrigeration performance because the heat from the box isn't being rejected and is carried back into the box.
- Pump is airlocked. This is very common if your boat has been hauled out of the water recently, or if the through hull pump intake came out of the water momentarily and sucked in some air. Many pump styles allow the stainless screws that hold the pump face onto the body to be loosened slightly so the pump face seal can be cracked opened allowing the air to bleed out. Otherwise the pump discharge hose or connector will need to be loosened to allow the air to bleed out so the pump can prime properly. The pump needs to be installed below the water line for this to work.
- There is a restriction in the sea strainer, pump suction or discharge hose. We have seen kelp sucked up against the through hull as well as clusters of baby mussels growing inside the pump tubing. Check your sea water strainer to make sure it isn't clogged (you do have a sea strainer, right?). You should have a 1/2 gallon per minute of flow for a small evaporator type system and 1.5-2 gallons per minute for a cold plate system. If possible, collect the discharge water in a bucket for exactly one minute and see what volume you have. If it's much lower than the recommended flow rate it may be partially blocked. Visually inspect the tubing, look for any possible kinks or blockages, and run some type of small wire or snake through the lines from the pump to the through hull and then towards the discharge to clear the blockage.
- Scale buildup inside the water condenser. Minerals from the sea water can buildup inside the water condenser itself, slowing water flow, reducing heat transfer and causing the system to perform poorly. Chemical flushes with an acid solution will help dissolve the buildup and improve system performance.
Problem: Your Frigoboat keel cooled conversion kit cools at first, but then provides no cooling while the compressor runs constantly. If you shut the system down for awhile and restart it, the same situation repeats itself.
-Moisture is in the refrigeration system and is freezing into ice at the inlet of the evaporator. We have seen this situation many times, and it seems to be a problem specific to Frigoboat keel cooled systems, usually after they have been installed for 10 years or so. Even though the system is sealed and nobody has worked on it, somehow moisture has made its way into the refrigerant. It circulates inside the system with the refrigerant and refrigerant oil, however as it leaves the capillary tube and enters the low pressure of the evaporator it instantly freezes due to the low temperature of the evaporating refrigerant. This creates an ice plug which stops all refrigerant flow within the system. The way to prove that it is indeed a moisture problem and not just a piece of debris, is to use a hair dryer or heat gun on the evaporator inlet while the compressor is running but not cooling. Once it heats up enough to melt the ice plug, you will hear a whoosh sound and gurgling that let you know that the refrigerant is once again flowing. The evaporator will begin to get cold, however the problem will certainly repeat itself. The solution is to call us up at 360-303-4912 and we will temporarily remove the compressor, change the refrigerant oil (it tends to absorb moisture) and the filter dryer on the compressor sled, then reinstall it. Then we will pull a long vacuum (to remove any additional moisture and noncondensables) and recharge with refrigerant . We have done this many times and it has always solved the problem.