Tuesday, October 3, 2023


Ask Dave: Do absorption refrigerator coils get cold spots as they age?

Dear Dave,
As our absorption refrigerator coils age, do they build up cold spots in them? If so, is there a way to restore them to complete function? —Donald

Dear Donald,
The tubing in the cooling unit of your absorption refrigerator will not build up “cold spots” with age. Rather, it can develop blockage if it is run in an unlevel condition.

How an absorption refrigerator works

The typical absorption refrigerator has a boiler vessel that contains a mixture of hydrogen, ammonia, water, and sodium chromate. The heat source, a flame when in LP mode and a heating element when in 120-volt mode, heats the mixture to a boil, which sends it up to the evaporator fins.

Click/tap to enlarge.

As you can see in this Dometic diagram, there is a chemical reaction and the components separate and travel back to the boiler vessel in a zigzag pattern by gravity only. Both Dometic and Norcold recommend the unit be level with a reference of 3 degrees side to side, 6 degrees front to back. This will allow the solution to flow and not “pool” at one of the bends in the tubing. Sometimes it’s hard to tell what is 3 degrees and 6 degrees, so they provide a bubble level that should be placed on the base of the freezer section.

If the bubble is halfway in the circle, it is good to use. Otherwise, the solution gets stuck or pools at the corner and will get hotter and eventually flake and cause a blockage. This prevents the solution from flowing and sometimes you will hear a gurgling sound as it hits the blockage and flows back the opposite direction.

Don’t park on a slanted driveway and run absorption fridge

This is a common issue with absorption refrigerators as owners bring their rig home and park in a driveway to plug it in and get ready for a trip. Most driveways are slanted for rain runoff. Since they are not sleeping in it, they may not realize it is out of level. Then they run the refrigerator for a couple of days to cool it down before leaving.

It is hard to determine how fast the flaking will start and how severe it will get. It depends on the temperature and how often the cooling unit cycles and the severity of the angle. However, the more you bring the unit to the house and run it while parked on the driveway, the more often you create the situation until it gets blocked and does not run efficiently.

Signs an absorption refrigerator may be experiencing blockage

We have done extensive work on a 1992 Norcold in an Itasca Suncruiser for The RV Repair Club, and that unit looks like it is brand-new. A telltale sign of a cooling unit that is experiencing a partial blockage is discoloration of the tubing or rusting. This is due to the extreme heat generated in an area and the powder coated paint peeling off.

Another sign is extreme heat, as the cooling unit typically will run at 250-300 degrees. When there is a blockage it can reach 800 degrees or even more. This unit had no discoloration and no extreme temperatures as it has always been stored and prepped for a trip inside a level building. The photo above shows the unit as we pulled it out to test.

So the best thing you can do to prolong the life of your absorption refrigerator is to make sure it is in a level position any time you run it.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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Dave Solberg
Dave Solberghttp://www.rv-seminars.com/
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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1 year ago

6 degrees front to back !!! Good luck sleeping !! We use the measure app…it works great…

Ian Anderson
1 year ago

Many of us have both gas and electric refridgerators. If you run on electric do you still get the same problems as you would running on gas?

1 year ago
Reply to  Ian Anderson

Yes you would. The only difference is how the solution is heated.

Donald Schneider
1 year ago

Thank you so much for the clarification and explanation on how the fridge works. Is there any fix if the spots have already started.
Thanks again

David Solberg
1 year ago

I have talked with some dealers and service centers that claim to be able to cut out the blocked part of the tube and weld in a new one but have not gotten any data of the cost or longevity? I have also talked with an Amish group that have been vendors at shows that have developed a different cooling unit. Maybe someone has tried them, however the cost was pretty high?

Tommy Molnar
1 year ago
Reply to  David Solberg

They convert your regular RV fridge to a compressor unit. I know someone who drove up to IN to get it done. They love it. But, you still have the small cu in inside space. And it runs on 12v all the time so you have to make sure you have enough battery power to keep it running. If you really want a compressor fridge you’re better off buying a 120v unit from Home Depot or Lowes. Or one of the fancier Furrion units. Even MORE money.

Bob M
1 year ago

They never provided me a bubble level. It’s also difficult to decide what surface is ok to level in the fridge or even the RV. Everything is a little out of kilter.

1 year ago
Reply to  Bob M

Same here. Never received a bubble level with any of my refrigerators. I used a torpedo level in the fridge. Get it level and then check other places that give the same reading. My counter top next to the refrigerator is the same. Now I use the app on my phone. It has a circle that turns green when level. Also shows how far from level it is.

1 year ago
Reply to  Bob

Hi Guys, a cool app I learned about from this RV news letter is called “Army Knife for Android” for android phones. This app contains a “flashlight, Unit Converter, Timer, Stopwatch, Compass, BUBBLE LEVEL (absolutely reliable), Calculator, Magnifying Glass, Mirror and a Ruler”. Phenomenal app!!! Thanks RV news letter for the tip. Dennis

Michael Galvin, PhD
1 year ago
Reply to  Dennis

ToolBox app is also great.

1 year ago
Reply to  Bob M

Bob: Place a bubble level at the highest point – i.e., on the flat floor surface of your freezer unit. The Rv floor may be near level – but the higher you go, the more it may be out of level.
You are trying to level the cooling unit in the fridge not the whole Rv! Safe travels – be well!

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