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Old 11-14-2018, 12:01 AM   #1
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Default Gas Absorption Refrigerator Mods to Improve Performance

I am putting this writeup here as this forum has the best technical feedback from members of any of the Class B forums I am involved with. I will also provide links to this post on the other forums to help those having gas absorption refrigerator problems. Some of my problems are particular to the Roadtrek 210P, and others are more general.

Roadtrek 210P Refrigerator Problem Solutions

The Dometic RM2554 refrigerator in my 2006 Roadtrek 210P had poor performance in hot weather with fridge temperatures into the mid or upper 40’s in hot weather. The freezer was good at near 0-degrees. The fridge worked a little better on gas than electric. So I started searching the internet and read the Dometic installation and service manuals to try to figure out if the refrigerator had failed or if there was a fixable problem. I will describe the steps that have made the fridge performance acceptable, though it does struggle sometimes in hot weather with temperatures going up to about 40-41 degrees. The refrigerator will get to the mid-30s in more moderate temperatures below about 85 degrees.

I checked the AC heater resistance and it met specs. I hooked the heater up directly to AC and there was no improvement.

I bought a fan called the Snyder fan system, which helped a little. The Snyder setup is no longer available, but I think there is a better fan setup than this that I will describe later.

The Dometic installation and service manuals showed that the vent area behind the fridge needs to be configured properly to get adequate venting. Roadtrek did not install the proper vent cavity setup. I do not know if Roadtrek has fixed the vent setup on the newer models. I installed an inner wall to eliminate the large gap between the van sidewall and the fridge coil system. I also put some foam insulation between the Van wall and this new inner wall to reduce solar heating of the outside wall from heating the vent cavity. The Dometic manual also says you can use a wall baffle but I thought the inner wall mod would work better. I also made an upper baffle as shown in the Dometic installation manual. I installed another fan as shown in the manual. The performance improved somewhat.

I had some inconsistent operation with the control board so I replaced it with a Dinosaur board.

Replacement boards for Dometic

APRV has some good information regarding problems with sidevent setups like our Roadtrek’s. I bought the APRV control unit and one of their fans. The APRV control unit protects the refrigerator from overheating caused by off-level operation, and also can control a vent fan. I installed the fan in the upper vent to pull air through the vent cavity.

https://www.arprv.com/rv-fridge-slide-out.php

I try to park the Roadtrek so the fridge side is shaded if possible. I have also made a small shade that attaches with suction cups to the outside of the Roadtrek to shade the refrigerator area and reduce solar heating.

I try to not put hot foods or a lot of room temperature items in at one time. I keep two small blue ice freeze bricks in the freezer, and I put these in the refrigerator compartment in hot weather during the day, and return them to the freezer at night.

I also have one of the small blue battery fans that blows air over the evaporator fins inside the fridge. This helps, but I may try some 12-volt fans that should give better airflow.

I think the cumulative effect of all these mods has brought the performance of the fridge to an acceptable level. I think the upper fan installation and bringing the vent cavity to Dometic specs had the most effect.

Another option is to have the cooling unit replaced. I have talked to Leon Herschberger at National RV Refrigeration in Indiana. He was very knowledgeable on the RV refrigerators and has rebuilt cooling units that sound like they are better than the Dometic original unit. If I were going to have my unit repaired I would strongly consider driving to his location.

National RV Refrigeration National RV Refrigeration
260-768-7059.
Leon Herschberger
5335 N SR 5
Shipshewana, Indiana 46565

I have read that some have had success remove the fridge and turning it upside down to “burp”. They claim they have had good fridge performance as a result.
Two-Way Refrigerator? - Page 8 - Airstream Forums

When this fridge fails completely, another option is to replace it with a compressor model. This would also require electrical system upgrades.
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Old 11-14-2018, 02:31 AM   #2
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It's not just absorption fridges that RV manufacturers fail to adequately ventilate. I've done a similar fix on my compressor fridge using a squirrel-cage fan (16cfm) to vent back into the living area of my class b since I don't have an outside vent. My idea is to keep the compartment temperature comparable to the living area since it can easily get 15-20 degrees hotter behind my fridge.

I like your use of a squirrel-cage fan for its' compactness and blower efficiency. I see how the exhaust air exits the vent, however I'm having a bit of difficulty seeing why the fan doesn't pull air from outside since it is a relatively small area on a large vent and is so near the vent exterior.
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Old 11-14-2018, 02:48 AM   #3
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It's not just absorption fridges that RV manufacturers fail to adequately ventilate. I've done a similar fix on my compressor fridge using a squirrel-cage fan (16cfm) to vent back into the living area of my class b since I don't have an outside vent. My idea is to keep the compartment temperature comparable to the living area since it can easily get 15-20 degrees hotter behind my fridge.

I like your use of a squirrel-cage fan for its' compactness and blower efficiency. Although I'm having a bit of difficulty seeing how the hot air leaves the exterior vent and why the fan doesn't pull air from outside since it is a relatively small area on a large vent.
You are correct on your concern about the fan pulling air back in from the upper vent openings. I forgot to include this in my writeup. Using foam cut from 1-inch insulation board I blocked the upper vent openings except for the the small fan exhaust area. The air blowing out is warm. The fridge seems to work better with this mod. This mod really helps when driving down the road, as air can only come out the upper vent, which is what you want.

In cooler weather I take the foam out as the fan does not run as much and the natural air movement is enough to cool the coils.

I would like to come up with a better looking way to block the upper vents.
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Old 11-14-2018, 04:13 AM   #4
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Sounds like you already thought about it. Is your fridge performing well?

I've traveled only in mild/cooler weather so far, so I cannot really say if my fan modification was necessary. But I have to feel it was warranted due to poor (actually, hardly any) original ventilation by Airstream. RV makers tend to place their fridges in tight, hot places in spite of manufacturer recommendations.

Here's my fan and the 1-1/4' exhaust hose, along with the small outlet vent (I had very little wall space options). My fan has the round outlet so that I could attach the hose. The blue switch in the second picture turns on the fan, which is also controlled by a 100 degree on/ 85 degree off button thermostat.
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Old 11-14-2018, 04:39 AM   #5
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Sounds like you already thought about it. Is your fridge performing well?
The fridge works well enough, but I have to be careful in hot weather. Even though the fridge will sometimes go up to about 41-degrees mid-day I have not had a food spoilage problem. Before I did the mods the fridge would go to the high 40's or even higher and we would have some spoilage then.
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Old 11-14-2018, 05:05 AM   #6
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I've had my 12v/110v Novacool compressor-fridge refrigerator section range from low 30's most days, up to low 40's a few times on warmer days. And these weren't hot days by any means.

Heat gain in a tin box is hard to control.
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Old 11-14-2018, 01:32 PM   #7
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Originally Posted by peteco View Post
You are correct on your concern about the fan pulling air back in from the upper vent openings. I forgot to include this in my writeup. Using foam cut from 1-inch insulation board I blocked the upper vent openings except for the the small fan exhaust area. The air blowing out is warm. The fridge seems to work better with this mod. This mod really helps when driving down the road, as air can only come out the upper vent, which is what you want.

In cooler weather I take the foam out as the fan does not run as much and the natural air movement is enough to cool the coils.

I would like to come up with a better looking way to block the upper vents.
You are correct about blocking All the upper vent openings except the exhaust fan(s), important. Why? The air 'feeding' the fan will take the path of least resistance which is not the air from the intake vents below. Although this was obvious, I still experimented with it, confirmed it. I use two 5.5 inch computer fans with gaskets which cover both of the two center vent openings completely. I have covered the two outside vent openings with Matte Black Adhesive-Backed Vinyl and also used a more glossy material.

Fan:

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

Gasket:

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

Vent covering:

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I drive using ac or propane.

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Old 11-22-2018, 08:38 PM   #8
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Hi Rowiebowie, I like your mod; where did you get your fan and thermostat switch? Thanks.
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Old 11-23-2018, 11:07 PM   #9
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Hi Rowiebowie, I like your mod; where did you get your fan and thermostat switch? Thanks.
Here's the text & pics from my post on airforums.com Declaring war on Interstate summer heat gain - Page 18 - Airstream Forums (see post #244). I didn't have an exterior vent outlet, so my goal was to just keep the cavity behind the compressor fridge at coach temperature by venting heat back into the living area and drawing in air that is generally about 20 degrees cooler (at least while the coach is occupied).


Originally Posted by rowiebowie:
I will install a fan to cool the area behind the fridge. As mentioned in another post, proper lower & upper venting for the nova cool 12/110v fridge was not on Airstream’s priority list.
I bought one of these 16/cfm fans https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 and a length of 1-1/4" ID flexible hose and wired it to a lighted wall switch I added. I routed the hose behind the wardrobe and out the panel above the rear tv using this 1-1/2" OD round vent cover https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1. The fan pushes a good amount of air, but of course, my mod changed the original ventilation path (if you can even call it that) I'm drilling a couple of 3-1/8" holes below the fridge in the cover to the Inverter/Fuses/Breakers/Battery Cut-Off and am considering closing off the microwave grill in an effort to pull air into the bottom and out the top. But probably not until I install a thermostat so I can leave the fan switched on.


Originally Posted by rowiebowie:
Update on insulating behind the Microwave in my '2012 Avenue:
Now to install the fan (above) to vent that area, the 100 degree on/85 degree off thermostat https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, on/off switch, and reinstall the microwave.

I had the microwave out the other day and finally took pictures of my switched & thermostat controlled fan to ventilate the refrigerator compartment (inadequately vented by AS). Due to the lack of cabinet wall surface to install a large vent, I went with a 16 CFM squirrel-cage fan that pushes air out a small 1-1/2" hose that runs behind the wardrobe and vents near the switch at the rear TV.



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Old 11-23-2018, 11:20 PM   #10
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Thanks for this, however Amazon links are bad here, but only blower one works if I go to Airstream forum. Weird. Now they all worked depending on where I grabed them...

Blower https://www.amazon.com/gp/product/B0...ustomerReviews

Vent Cover
https://www.amazon.com/gp/product/B0...&ie=UTF8&psc=1

Thermostat switch
https://www.amazon.com/gp/product/B0...&ie=UTF8&psc=1
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Old 11-24-2018, 12:51 AM   #11
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It's been about 10 months since I ordered them off Amazon, but you found them. Thanks for updating the links.
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Old 11-24-2018, 05:33 PM   #12
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Default Fridge woes

My class B, a 1973 Hall GTC, has the original Trav’ler 3-way reefer, which still works well. The fridge has minimal electronics and nothing is automatic except the thermostatic controls: everything else is controlled by manual mechanical switches at the whim of the operator. There is literally no board to fail, so it doesn’t. The coach builders were hip to the needs of gas operated refrigeration and provided a minimum of 1.5” high density foam insulation not just behind the refrigerator cavity (chimney), but the entire coach as well. The makers of the fridge clearly called for two vents for proper operation: one at the top to let the heat out, and one on the side at the lower end of the cooling coils to let the outside air in. For a system to operate as designed there Must be a method of providing adequate airflow without returning the heated air to the living space of the coach. My question is, if the fridge doesn’t work well, why not install an actual roof vent? It seems that a lot of effort is going in to getting things to work without actually following the installation instructions of the refrigerator’s manufacturer. Or am I missing something?
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Old 04-14-2019, 04:25 PM   #13
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Thumbs down Gas Absorption performance mods

Quote:
Originally Posted by peteco View Post
I bought a fan called the Snyder fan system, which helped a little. The Snyder setup is no longer available, but I think there is a better fan setup than this that I will describe later.

I think the upper fan installation and bringing the vent cavity to Dometic specs had the most effect.
Can you give some more guidance/pictures on the installation and airflow behind the unit? My unit (Roadtrek Adventurous RS) seems to comply with the Dometic installation requirements (see pic, looking down from upper vent), but I can see where better direction of airflow could improve performance. I am thinking having a pair of computer style fans exhausting the upper vent would be a help, and see where insulating the exterior wall could also help.
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Old 04-14-2019, 09:45 PM   #14
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It is hard to tell from your picture if it meets Dometic install recommendations. One thing that looks like it could adversely affect cooling is the large gap between the evaporator fins and the wall or exhaust grille. I modded mine to eliminate this gap.

I am in Hampton VA, where are you in VA? I would be glad to look at your setup and make recommendations.
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Old 04-14-2019, 11:28 PM   #15
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Default Gas Absorption performance mods

My dometic manual gives 20mm space and I am sure there is more than that. I am thinking some insulating material and a baffle so that rising air is directed only thru rather than around the fins, plus some kind of booster fan(s) exhausting at the top would improve things. Would likely put 1 or 2 12v fans on a thremotatic switch triggered by temp in top space.

I am located in Springfield VA. Will be going down the penninsula in mid May.
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Old 04-15-2019, 02:03 AM   #16
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One thing that looks like it could adversely affect cooling is the large gap between the evaporator fins and the wall or exhaust grille.
Sorry, I meant to say condenser (not evaporator).
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Old 04-15-2019, 02:15 AM   #17
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Here is a sketch from a Norcold install manual. It makes sense to me to make sure the baffle extends all the way up to the condensor fins so all the vent air passes through the fins. This is essentially the baffle box design I added to my 210.
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Old 04-15-2019, 02:30 AM   #18
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Peteco is definitely correct in his baffles, closer is better. This is a classic gravity chimney so all the same "rules" apply as they would to any other application. I think his setup is quite good.



Any hot area should be baffled horizontally so air can only go in the bottom and out the top creating maximum velocity from the heat rising. No "cold" areas should be able to pass any of the air from low to high for the same reason.


If you have two hot areas, and especially if one is lower than the other, it is best to have a vertical baffle between them if possible. To prevent the heat from the lower one going through the higher one. Essentially just two chimneys of the smallest area possible. In an RV gas frig, the boiler is usually much hotter than the condenser air and has lot of hot exhaust gas, so isolating it is a good idea.



Fans will work the best if right at the inlet or exit of the chimeys or ducted to those areas either as a push or pull fan. If not directly blowing or sucking the chimney air, the fans will often just "loop" the air they have. This especially true on upper Roadtrek vents unless you block off all of the vent except the fan blowing out area, to prevent looping. Ducts to the chimney tops essentially do the same thing.
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Old 04-15-2019, 02:40 AM   #19
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In an RV gas frig, the boiler is usually much hotter than the condenser air and has lot of hot exhaust gas, so isolating it is a good idea.
I have considered trying to wall-off or isolate the boiler to keeps its heat away from the absorber and condenser. It would probably help but the fridge is now working OK so I haven't bothered with it.
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Old 04-15-2019, 02:53 AM   #20
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Fans will work the best if right at the inlet or exit of the chimeys or ducted to those areas either as a push or pull fan. If not directly blowing or sucking the chimney air, the fans will often just "loop" the air they have. This especially true on upper Roadtrek vents unless you block off all of the vent except the fan blowing out area, to prevent looping.
I think the Dometic recommended fan location does cause "looping" of the airflow inside the vent cavity. I had poor fridge performance with the fans located in the middle like Dometic recommends. I have found the upper exhaust duct location with a centrifugal fan to work well, but "short circuiting" of the exhaust air back into the exhaust duct is a potential problem. So in hot weather I have blocked off all the exhaust duct opening except for the fan exhaust. This has improved the performance while driving as well as no air can be forced into the exhaust duct. Another benefit is keeping rain out, which is especially a problem with the 210 and its curved wall. Other vehicles with a straight vertical wall should have lesser problems with water intrusion. I remove the exhaust duct blocks in cooler weather to allow natural convection of the air.
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