Gas Absorption Refrigerator Mods to Improve Performance

[engnrsrule]

Gas Absorption performance mods

I have a Dometic 3 way fridge in a 2006 Roadtrek Adventurous RS. I have been following this thread to help troubleshoot what I thought was poor performance on propane. I discovered it was actually NON-performance on propane, caused by the thermistor wire being slightly unplugged from the control module. fixed that and back in business.

However the good info here inspired me to add the wireless thermometer, which is great, and to add fan cooling to the rear of the refrigerator compartment.

I used two arctic F9 Silent fans, mounted to the removable grill, and wired to a SPDT switch allowing me to select manual on or thermostatically controlled operation (with an off position as well). The fans have very low draw. I added a baffle to direct most of the rising air into the cooling fins. I selected an adjustable thermostatic switch (set "on" from 90 to 130), as I felt like I would need to adjust or tune for varying conditions.

The two fans draw less than 1/2 amp total, and are very quiet. They do not move a lot of air, but they do produce a positive draft bottom to top through the fins which will certainly help.

The fan mod and baffle installation cost about $36. The key parts I used were:

- AcuRite 00986M Refrigerator/Freezer Wireless Digital Thermometer $20
- ARCTIC F9 Silent, 92 mm Fans with Standard Case (2) $6 each
- NTE Electronics 54-240W Waterproof Illuminated Rocker Switch, SPDT $8
- Emerson 3F05-1 Adjustable Snap Disc Fan Control $12

Pictures show the baffle in place, the interior switch location (in the vented trim around the microwave), the thermostat switch located above the cooling fins, and the fans. I used connector plugs to facilitate easy disconnection if the fridge ever had to come out, or to remove the grill. I put tabs on the thermostat to hold it against the fins and put a nylon tie to keep it in place.

Feel free to respond if you have any questions.

 

[windymatt]

Very tidy setup! What is the advantage of the baffle? Does your rig have an exhaust stack, and if so, would locating a fan up there be as effective?

 

[engnrsrule]

No vertical stack. The "boiler" exhausts to right of the fins and that heat also exits top vent. The baffle forces all rising air to go past the fins, the fans draw the air in the bottom vent and out the top vent.

 

[DaveWA]

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/B00314J422/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

Gasket:

https://smile.amazon.com/gp/product/B007EFLN64/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

Vent covering:

https://smile.amazon.com/gp/product/B00NQMLVUM/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

I drive using ac or propane.

Bud

I am considering making the mods that you employed. I have a Dometic RML 8555 and I think that the performance would benefit from better ventilation. I wonder how the aftermarket computer fans hold up over time, being somewhat subjected to the elements when positioned up against the vent (my fridge/van has two vents; a lower intake and upper exhaust, and I would install both on the exhaust vent). The 8555 does already have one extra fan that is positioned about mid fridge (below the fins), but this position is protected the from the weather. It turns on when the ambient temp rises above some set temp.
Have you found your fans have been reliable?

 

[engnrsrule]

DaveWA, I have found the computer fans to be pretty reliable. On the inside fridge fans assembly, which has 2 fans, one went out after 6 months. See picture. Changing it was not a big deal. The fans serving the outside have been going 2 years without a problem and I also increased from 2 to 4 fans, which are controlled by a thermostat. I agree with you about sealing the gap space around the top. That can only make it better.

I am very happy with the new Dometic, upgraded to a RM8501. I like that the inside is convertible to all fridge or fridge plus freezer. I like the auto switching, but do not use it because it doesn't follow my priorities...It wants to run on propane while driving and I prefer 12v if the engine is on.

This is the in fridge fan. Runs off 12v and power can be fished up through the fin condensate drain tube. https://www.amazon.com/gp/product/B089BWZ3PX/

 

[GeorgeRad]

Good info about fan bearings, https://www.gamersnexus.net/guides/779-computer-case-fan-bearing-differences

I have a Noiseblocker fan with ball bearings on my fridge. It is much quieter than the original factory fan on Isotherm compressor fridge.
https://www.blacknoise.com/site/en/...it-fans/nb-eloop-series/120x120x25mm.php#tab1

 

[Bud-ClassB]

I am considering making the mods that you employed. I have a Dometic RML 8555 and I think that the performance would benefit from better ventilation. I wonder how the aftermarket computer fans hold up over time, being somewhat subjected to the elements when positioned up against the vent (my fridge/van has two vents; a lower intake and upper exhaust, and I would install both on the exhaust vent). The 8555 does already have one extra fan that is positioned about mid fridge (below the fins), but this position is protected the from the weather. It turns on when the ambient temp rises above some set temp.
Have you found your fans have been reliable?

Yes, but ymmv.

Bud

 

[DaveWA]

Yes, but ymmv.

Bud

Completed the modifications. I got my fans from CoolerGuys.com. They had waterproof fans, and they suggested that I install a super quiet, low amperage draw low speed fan, as well as a high speed fan. I used one of their controllers that can be programmed to turn on and off the fans at prescribed temps.
All went well with the installation. Now I just need to see if performance improves when the outside temp is in the 85 plus degree range. Attached are the pictures and contact info for CoolerGuys.

 

[engnrsrule]

Looks good. There are two changes I made since original post. Many folks advocated for fans inside the fridge. I added these which I like because they attach easily and have an on/off switch. I also blanked off open space in the grill. I thought I recently had a fan go bad but it was actually just a bad soldered connecting in the plug. They are so inexpensive I bought a couple of spares.

Running 2 weeks in 80's and 90's the fridge temps stayed very stable.

I will add that the placement of fans exhausting at the top is best way to go. Even though these are not waterproof, they are tending to blow any intruding water out. Also the top location has the fans working with and not against natural convection.

 

[Bud-ClassB]

Completed the modifications. I got my fans from CoolerGuys.com. They had waterproof fans, and they suggested that I install a super quiet, low amperage draw low speed fan, as well as a high speed fan. I used one of their controllers that can be programmed to turn on and off the fans at prescribed temps.
All went well with the installation. Now I just need to see if performance improves when the outside temp is in the 85 plus degree range. Attached are the pictures and contact info for CoolerGuys.

Thanks, had not thought about 'waterproof' fans. Will when replacing.

Bud

 

[DaveWA]

How did you route the switch wires from behind the fridge to near the microwave? Did you need to pull the microwave out or the fridge out? I pulled 12v from a connection block on the back of the fridge, but the problem is that the controller is powered whenever 12v is turned on, or when I am plugged into shore power (as the charger runs and apparently bypasses the 12v cutoff switch). On a hot day, when the van is stored, fridge turned off and van plugged into shore power, my new fans will run if above the set temps. I like the idea of a convenient fan shut off switch near the fridge like you set up. I tried to find power on the back of the fridge that was switched to the fridge on/off switch that I could pull the fan power from, but could not.

 

[engnrsrule]

How did you route the switch wires from behind the fridge to near the microwave?

There are two answers to the question. Initially, I tapped the 12v from the furnace, located under the microwave. My microwave has a wooden trim piece that was easily removed, where I mounted the switch. I took the "pantry" slider out to route the 12v to behind the fridge. Because there is combustion it is very important to ensure good seal where the wires penetrate.

The 12v circuit that serves the fridge is hard to find. It is near the front top of the fridge and the area is sealed to prevent combustion gas from entering the cabin.When I had the new fridge installed, I mounted a terminal strip on the wall in back of the fridge below the 120v, and asked the shop tech to split a feed from the fridge 12v supply. I used that terminal strip to power the exterior and interior fridge fans. Now the fridge and its supporting fan systems are on the same 12v circuit. The fans are still able to run if the fridge is turned off, but if you pulled the 12v fuse it would kill the fans too.

 

[DaveWA]

Thanks for the tip. I will check for the circuit that runs the fridge and see if I can tap that. If so, I might just pull the fuse for now when in storage to keep it simple.