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RV ‘Gremlins’, Part 3: The secrets of RV absorption refrigerators

This series features what I call “RV Gremlins,” those pesky little troublemakers that seem to pop up out of nowhere and then just as quickly disappear. In Part 1, I looked at the gremlins that live in lead-acid batteries. In Part 2, we looked at the mysteries of 12-volt wiring. Today, we’re trying to figure out the gremlins in RV absorption refrigerators.

Appliances

Everything works fine when the rig is sitting in the driveway getting ready to take off on a trip, but the minute you plug into the campground source it either doesn’t work or doesn’t work efficiently enough. I get questions every day about how something worked fine for several weeks, then it didn’t, only to start working again. Let’s take a look at some of the major appliances and what situations, or “Gremlins,” they have.

RV absorption refrigerators

The key to getting an absorption refrigerator to cool efficiently is understanding how it works and the factors that can affect its operation and efficiency. Dometic and Norcold are the two most popular absorption refrigerators and work pretty much the same. They utilize a cooling unit in the back that has a container called an absorber vessel with a rich solution of ammonia, hydrogen, water, and sodium chromate.

A heat source from either a flame from LP or a 120-volt heating element heats the solution. This then causes vapors and gases to rise up the pump tube to the condenser fins at the top, the freezer section.

How RV absorption refrigerator systems work

The short version of explaining how it works is that several chemical reactions and flashes happen in the cooling unit and all the rich solutions must zig-zag back down the cooling unit tubes by gravity. If the rig is not level, it could cause the rich solution to pool or stop flowing in an area. If this happens, it will get very hot and start to dry out and flake, eventually stopping the flow and ruining the cooling unit.

This is a common problem as most RVers bring their rigs to their house before taking off for a trip to cool the refrigerator down and pack the unit up. Most driveways are slanted for rain runoff and are beyond the acceptable level recommended by the refrigerator manufacturer. They recommend no more than 3° side to side and 6° front to back. They also provide a bubble level to show what is acceptable. However, most owners don’t think about being level as they are not sleeping in it and don’t notice the angle. As the cooling unit gets more and more plugged, it becomes less efficient until it stops cooling.

A graph of the RV absorption system

RV absorption refrigerator gremlins

Where do the gremlins hide? All refrigerators cool efficiently to below 40 degrees when the ambient temperature is cool, like in the 65-70 degree range, unless the cooling unit is plugged more than 50 percent. If you are having insufficient cooling, check the operation on both LP and 120-volt modes. If it works as designed on one mode and not the other, it indicates the cooling unit is fine, just a gremlin in the mode that is not working.

However, if it’s not working efficiently on both modes, check the thermistor on the evaporator fins as this is the temperature monitor for both modes. If it is placed too low and in the middle of the fins, it will sense a lower temperature and not turn the unit on as often. If it is covered in frost or ice, it will indicate it’s cold enough. Keep in mind these units are not self-defrosting, so you will need to keep an eye on the freezer and evaporator fins especially if the next issue happens!

How to get the system to work the most efficiently

Warm, moist air and poor air circulation can cause hot and cold pockets in your refrigerator. This not only causes excess frost but also inaccurate temperature readings. Check the door seals periodically to make sure they seal properly by placing a dollar bill between the door and the refrigerator frame and shutting it. When you tug on the bill, it should have a slight resistance. If not, it’s letting air from inside the rig into the refrigerator cabinet and it will cause the unit to work harder and not cool efficiently.

This is a common issue as RV owners like to put heavy liquid containers in the door shelves just like at home for easy access, and then bouncing down the highways causes the door hinges to bend or settle. The warm, moist air from inside your rig will cause additional frost and ice buildup and inaccurate temperature readings.

Do not load your RV’s absorption refrigerator with warm food or canned food that is not cooled. Try to bring everything down to below 40 degrees fast. Make sure you have good air circulation in the cabinet—do not line the shelves with plastic or anything that will restrict good circulation. I recommend using a 9-volt fan to help move air inside the cabinet.



Last check: The house batteries

Another issue could be sulfated house batteries. The module board needs 12-volt DC power on both the LP and 120-volt side, as the eyebrow board runs on 12-volt and provides information to the module board. If you are having intermittent issues or insufficient cooling, use the 12-volt power booster to identify it’s not the house batteries.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook.”

Read Part 1 of his RV Gremlin series here, and Part 2 here.

Read more from Dave here

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##RVT1060

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CLeeNick
2 months ago

Since we bought our new trailer, our old Class C has been “mothballed” for the most part. We use it occasionally for non-rv owning family when they come to visit. On such an occasion last year, I lit the fridge prior to arrival to make sure it would still cool down. It’s never failed. This time, after a day of being lit, it didn’t get cold at all. That had never happened, and I figured it had finally given up the ghost. I checked for all the common culprits. Nothing amiss. So I turned it off and began the mourning process for my soon to be dearly departed money. About 45 minutes later, I remembered to open up the doors on the fridge. Habit really, so it doesn’t get moldy. When I did, the dang thing was ice cold, AFTER being turned off for 45 minutes! I lit it again, and it worked perfectly. Only thing I can figure is there was some sort of bubble in the cooling system that kept the ammonia coolant from circulating, and the temperature changes broke it loose. Weird!!

CCreek
2 months ago

I love our Dometic. Very adaptable. Except ice cream is a no go.

Bob p
1 month ago
Reply to  CCreek

Ice cream requires 0 degrees or below, these fridges can’t get there.

Dennis
2 months ago

Back when the earth was cooling, we owned a 2003 Newmar DSDP with a Dometic 3Way fridge. In the 9 years we owned our DP, the fridge never failed us didn’t matter if the ambient was-10 or +30 degrees C. It worked perfectly.
Then we bought a 2016 LTV with a Dometic fridge and it never worked properly from day one. One day it worked adequately, the next day, not so much.
The latches on both the fridge and freezer doors broke in the first few weeks. LTV sent new latches and warned that they were a problem. We didn’t have the LTV very long and decided we would just give up RVing and sold it.
We sure do miss our old Dutchstar. They just don’t build em like that anymore.

Bob p
1 month ago
Reply to  Dennis

WHAT..? Are you insinuating the earth goes through heating and cooling cycles and the present “global warming” is normal. Well gee whilikers imagine that! I’m old enough to remember back in the ‘70s we were heading into the next ICE AGE, that didn’t happen either.

Genevieve Arthur
2 months ago

Our norcold works very well on 120v now since we corrected and installed baffling above the unit. In addition, we added insulation around all sides to avoid any stagnant air pockets. HOWEVER….we still have poor cooling when on LP mode. We can’t get a clear answer as to why.

CLeeNick
2 months ago

Have you checked your LP regulator? When we bought our old Class C 16-17 years ago, the LP system seemed to work fine. Furnace, stove, water heater all worked. But the fridge would only work on AC power, it would not cool down on LP. I started asking around at local RV service centers and was assured if it worked on electric, it could be made to work on LP, as both modes use the same cooling system, just with different heat sources. (The AC heating element replaces the LP flame but they both do the exact same thing). I was thinking I would be replacing burner parts in the fridge, until someone mentioned the rigs LP regulator. I hadn’t even considered it, as every other LP device appeared to be working perfectly. It was mentioned to check “water column” (pressure) and other tech stuff, but at the time, a new regulator was like 10 bucks, which was way cheaper than a device to measure “water column”. Bought the regulator, installed it, and the fridge worked.

Edd M Langdon
2 months ago

Our refrigerator would constantly freeze our food no matter where I placed the thermostat, so I bought an exterior temperature controller with a long sensor. I drilled a hole in the side of the fridge and put the sensor on the back of the middle grate. This works great but only on electric. I found a way to install the temperature regulator by the refrigerator.
https://smile.amazon.com/gp/product/B00V4TJR00/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

Dave Mckenna
2 months ago

It’s easy to forget about the fridge when I stop unexpectedly at a less then level spot, or park on a driveway. I have installed the ARP Fridge Defend device on my class A, and travel trailer refrigerators. It takes the guess work out of wondering if I’m close enough to level and automatically prevents damage to the unit. An ounce of prevention……

Billinois
2 months ago

A great deal of leveling issues could be solved if the manufacturers would design a gimbaled system for the cooling unit that would keep it level in uneven locations. Similar to what boats use for appliances.
But I suppose the cost would be too great for the benefit.

Tom H.
2 months ago

I’ve also been told to not store food in plastic containers even those that come from a store. The plastic absorbs the cold not the food. At least that’s what I’ve been told.

Bob Palin
2 months ago
Reply to  Tom H.

Absolute nonsense.

George
2 months ago

6 degrees of tilt, through the center of an 8′ trailer width is 5″. Across the entire 8′ length it’s 10-1/6″. That’s a pretty large margin of safety in my book.

My “internal level” would never let our trailer rest outside these limits, ever. Nope, just couldn’t do it. We have owned our 2005 Nash 19B for 17 years and, aside from replacing the fridge burner once, have never had a problem with it.

Safe Travels all,

George
2 months ago

RV Fridges work best, in my opinion, when full. We never “run it to cool it down” we fill it with goodies from our house fridge, and freezer, and then start it up. We’ve never had a problem.

Thanks.

Leonard Rempel
2 months ago

The best way to get an absorption fridge to cool? Replace it with a residential unit like I did, AFTER I had a fridge fire! No wonder they are a leading cause of RV fires. I was lucky to catch and put out the fire in time before the whole rig went up in flames! This is in a 2020 Montana 5th wheel, so it just should not have happened, but sadly it did.

Last edited 2 months ago by Leonard Rempel
DMin
2 months ago

What if your fridge is consistently too cold? Over the winter we were in the southwest and had to set the fridge as warm as we could to keep things from freezing. Now, in the summer in the Northeast we have turned it a little cooler and it’s still barely staying above freezing. We keep it level as we can and turn it off if we aren’t. We are constantly turning it off and on to keep from freezing.

Bill T
2 months ago

They recommend no more than 3° side to side and 6° front to back. Is this referenced to the refrigerator or the RV? “Front to back” is it looking at the fridge doors or the front of the RV? Some fridges are facing the side of the rig while others are facing the front. Thanks.

Snayte
2 months ago
Reply to  Bill T

The refrigerator. The recommendation is coming from the refrigerator manufacturer so they would be referring to that unit

Snayte
2 months ago
Reply to  Snayte

Which brings up another point. Check for level in the fridge. It may not have been installed squarely in the rv.

Bill T
2 months ago
Reply to  Snayte

Thanks for the info. I thought it would. Just wanted to verify. Cheers.

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