Frig Operation

[BillB800si]

Thought this may be of benefit to some RV’ers.


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RV / Absorption Type Refrigerators are Different
Thursday 05th, September 2013 / 03:50 Written by Steve Roddy

Many RV’ers find out the hard way about the differences of a Residential Refrigerator and a Recreational Vehicle Refrigerator. Every RV’er must realize how their RV Refrigerator is going to perform differently and it certainly helps if you know why.
Residential refrigerators have pumps, motors and fans to help with air flow and refrigerant flow. They are also connected to a constant 120 volt power supply. RV Refrigerators do not use pumps and are frequently disconnected from AC voltage or switched to LP gas operation. The entire cooling process is completed by gravity.
I will try to keep it as basic as possible. The refrigerant that is used is ammonia. It starts in a diluted solution of water and ammonia. Ammonia is naturally attracted to water. Then some guy named Boyle comes along and makes a law (it is a law and not just a suggestion) that says liquids under pressure will have increased boiling points. We need to separate the refrigerant (ammonia) from the water. This is done by heating the water/ammonia solution, that is under hydrogen pressure, to the boiling point of ammonia and under the boiling point of water. This is why the amount of heat produced by either the gas flame or the electric heating element must be precise. Boiling the ammonia only will give us the refrigerant needed to make the RV Refrigerator cooling process begin. Ammonia vapor must be cooled at the top to return to ammonia liquid. Here is one area that a natural air flow is important.
The outside vent system uses two vents. One mounted on the sidewall at the bottom of the refrigerator, and the other on the roof. Or if your refrigerator is in a slide room your RV will have two sidewall vents. One at the bottom of the refrigerator and one at the top of the refrigerator. We all know warm air rises so the vent system creates a natural movement of air without the use of fans. Warm air created from our heat source, gas flame or electric heating element, as well as the heat that has been removed from the interior box escapes through the top vent. As the warm air rises, cooler air is drawn in the lower vent. This is why the RV Refrigerator may perform more efficiently in cooler temperatures.
Another part of the process that we depend on natural air flow is inside the refrigerator. Once again warm air rises. If you look inside the refrigerator you will see cooling fins located at the top. This is where the heat is absorbed out of the box and transferred to the coolant. Warm air rises to the top and the cooler air falls to the bottom. Once again we have air movement without the use of a fan. It is important that the interior is not overloaded with food or large containers. Never use paper towels or anything else that will cover the wire shelves provided. All of these examples will slow the air flow process and reduce efficiency of the cooling process.
The larger refrigerators will use additional cooling fans mounted midway on the back of the exterior. Never add fans to the lower area. This is the easiest place to mount fans and access a power supply but you will be cooling the area we are trying to create heat. Fans in the center area will increase air flow without decreasing temperatures from the flame or heating element. Also an aftermarket fan can be added to the interior to increase air flow if you have the normal overloaded refrigerator. This fan normally operates with a flashlight size (D cell) battery and would be located on the bottom shelf.
There are only a couple of models that are Frost Free RV Refrigerators. Most must be defrosted manually. A tip to perform defrosting slowly without the mess would be to increase the interior box temperature at night so that the ice buildup will slowly melt. One common misconception is the temperatures are much lower because of the ice. We see ice, the refrigerator must be extremely cold. Actually it is the opposite. Ice will mean warmer temperatures in the box. With ice covering the cooling fins they can no longer transfer the heat to the coolant. The only heat being removed is between the cooling fins and the ice which only results in thicker ice.

Read more at http://www.rv123.com/blog/rv-absorption-type-refrigerators-are-different/#8bcZxoQomDO1fEsp.99


Read more at http://www.rv123.com/blog/rv-absorption-type-refrigerators-are-different/#8bcZxoQomDO1fEsp.99

[John___Angela]

Great write up. Thanks for posting. I would think within the next 10 years absorption fridges will be in a continuous decline in the RV industry as compressor technology becomes more efficient, solar panels get cheaper and LED lights become mainstream. More and more RV's are coming stock with residential fridges. I suspect absorption fridges will have a place in the market for years to come but I can't imagine getting an RV now with anything but a compressor fridge. Already replaced the big NORCOLD in the A and waiting for the Dometic to die in the C. As long as it works though we'll keep it...although Angela would love the extra room of a compressor model replacement.

[tenbear]

Thanks for the description of Absorption Type Refrigerators. I had a general idea of how they work but you have given me a better understanding.

One thing I didn't see is the question of "how level". There have been many threads on this subject with some people saying that absolute level is required, while others say the spec'd within 6 degrees front to back and 3 deg side to side is good enough. What is your take on this?