Adding fan behind refrigerator...worthwhile??

[SJ-Chris]

I have 3 RVs and I seem to be addicted to adding stuff to them....lol.
They each have a standard Dometic 2852 absorption refrigerator. They seem to be working as expected. I did replace the cooling unit on one about 2 years ago and it has been working flawlessly.

My question is this... Under NORMAL OPERATION how hot does it get behind the refrigerator in the cabinet area and venting area out through the roof? And does adding a fan back there do much of anything to help with refrigerator operation (keeping interior of the refrigerator/freezer cool)? I'm not talking about preventing overheating and/or fires...just wondering if it helps the refrigerators perform better.

Something like this with some sort of thermostat such that it's not running all the time:

This particular fan moves ~38CFM at 45dB (might be louder than I'd like, but behind a refrigerator would probably muffle the noise quite a bit). Maybe I could find something quieter...
Here is a nice but simple 12v thermostat that could be programmed to turn the fan "on" when it hits a certain temperature and then turn it "off" once the fan cools it down to some lower value.
https://www.mpja.com/Single-Zone-Intelligent-Thermostat-Temperature-Controller/productinfo/34757+MP/

Let me know what you think. Total waste? Or significant increase in summertime cooling inside your fridge? I sometimes camp or lend out my RVs in 100+ degree summer temps.

Does anyone have any "before and after" data points or personal observations after having added such a fan?

Thanks!
Chris

[ernie1]

Am I to understand that the cycling temps of the cooling fans are 95degF on and 130degF off?

Exactly where is the best locations for the cooling fans in a refrigerator with side vents?

So is there to not be any space between the sides of the refrigerator and the fins of the cooling unit?

[enblethen]

Have you checked the distance between the cooling unit and the rig's outside wall? Normally installation direction say it should be only about 3/4 of an inch.
I closed mine up with foam board attached with Liquid Nails type material.

[SJ-Chris]

Test update: I just went and checked on my refrigerator temps (...the RV is sitting in storage and the refrigerator has been running for 24hrs). Checked at 3pm. The temps outside are 96F degrees (...pretty toasty!). The freezer temp was at 10F degrees and the refrigerator was at 40F degrees. I can see that the refrigerator low temp overnight was 33F degrees. I think overall this is about the best I can hope for.

-Chris

[SJ-Chris]

Added a 3rd fan and repositioned a few things. Cleaned up the wiring. I'll be taking it out in a week and we'll see how it does. This next trip will only be in ~80 degree weather, so I don't know if the fans will come on often and/or be of much help. The real test will be the next time I am boondocking in 95F+ temps.



These 3 fans will move 15cfm x 3 = 45cfm in theory. Running a test right now in ~94F temps while in storage.

-Chris

[hotjag1]

I wired a 4" 12v fan in the back of the refers on both of our motorhomes. The Allegro has side vents and the Isata has a roof vent. The fans made a difference on both RV's keeping the refers in the high 30's to 40 degrees on 90plus degree days. I turn them on manually with a switch when needed.

[SJ-Chris]

bucky wrote:


Roof vent systems vent themselves.
Side vent systems normally found in slides need help which is shy those systems have fans as they don't self vent as well as reef vent designs.

While it is true roof vent systems vent themselves (via the fact that hot air naturally rises), assisting this airflow (ie. adding fans) helps the process and appears to make the cooling happen faster, colder, and also using less propane when not hooked up to electric. My motivation was 99% just trying to make my fridge/freezer a little colder. With the 2 fans I added, the fridge/freezer is running 6 degrees F colder. For a $25 modification, I consider that a success/worthwhile.

I don't have a side vent system (found in slides), but it is easy to understand that naturally they will not vent as well since they don't have a roof vent. For those designs assist fans would appear to be even more helpful (or necessary).

Obviously, if someone is happy with their fridge/freezer temps then no modification is necessary.

Stay cool!
Chris

[fyrflie]

One thing I found this winter , when I replaced my frig cooling unit, was that the area above the fridge was not blocked off from the backside ventilation area. So any heat generated by the frig would rise up and fill that void, then eventually push into the coach.
Before I slid my fridge back in, I installed a piece of sheet metal to block off that void area and keep the heat rising up and out the roof vent.
My thought is that the efficiency of the refer depends largely on the removal of heat from around the cooling unit, so any effort made to assist that process can only help.

[bucky]

This issue needs two different discussions.
Roof vent
Side vent

Roof vent systems vent themselves.
Side vent systems normally found in slides need help which is shy those systems have fans as they don't self vent as well as reef vent designs.

[SJ-Chris]

enblethen wrote:
I would not tap any wires. Power the fans up off the 12-volt Red and Black. Install a manual switch or route through small thermostat.

It is running through a thermostat. But as currently wired, the thermostat always has power, and if the temps rise enough (even if the refrigerator isn't on), the fans will go on....even if the RV is in storage. Yes, I can open the side panel and disconnect the power to the thermostat (...I have easy connectors on the power lines to the thermostat), but I'd rather just have it wired to the "Fridge on/off" power so that it will never be on if the fridge is not on.

-Chris

[enblethen]

I would not tap any wires. Power the fans up off the 12-volt Red and Black. Install a manual switch or route through small thermostat.

[SJ-Chris]

Finally got around to adding some fans behind one of my Class C RV's refrigerators to try it out.

Two of these fans....
https://www.amazon.com/gp/product/B08FBP2ZM5
0.25amp, 15CFM, 32.8 dBA (Each)
$9 each

One of these thermostats....
https://www.amazon.com/gp/product/B0B2WTPJ3G
~$4

~$3 worth of other wire, zip-ties, etc.

$9 + $9 + $4 + $3 = $25 modification

Tested this on back to back days that had identical daytime high 90 degree temps.

Started with the refrigerator on for 24hrs prior to starting the test. Only opened the doors to check the temp after they had been closed for 24hrs.

With the fans OFF, at 3pm in the peak of the afternoon heat, the freezer was 11 degrees F and the refrigerator was 43 degrees F. (warmer than I would like)

With the fans ON (the next day), at 3pm in the peak of the afternoon heat, the freezer was 6 degrees F and the refrigerator was 37 degrees F.

Result: 6 degrees cooler with the fans on (thermostatically controlled) behind the refrigerator.

I consider it a win. I plan on adding one more fan (...might help another 1-2 degrees) and cleaning up the wires a bit. Will probably add to one of my other RVs that has a fridge that runs at about 40 degrees F during the heat of the day.



One last thing for me to figure out....I'm sure someone here can assist...
Currently, I am tapping 12v power off some easy to access wires (the orange and white wires coming from the right side of the photo). I thought they would only be hot (have power) when the refrigerator was on. I was wrong though...they are always hot/on.

Can someone tell me which of these wires is ONLY hot/12v when the fridge is turned on inside the RV? Is it the red wire that I marked with the yellow "A"?



Thanks!
-Chris

[Cummins12V98]

My last DRV had the frig in the slide with the two vents on the slide outer wall. I cleared out all the loose insulation so it had a clear path from lower to upper areas. I then added a small computer 12V fan to the back side of the upper vent. I placed it on a 12V switch. The temp drop in the frig was remarkable!!!

[pianotuna]

Hi Chris,

I can't give you an exact temperature--but I can say that in the winter time my thermo cube turns on at 35 f and off at 45 f.

https://www.amazon.ca/Farm-Innovators-TC-3-Thermostatically-Controlled/dp/B0006U2HD2

[SJ-Chris]

pianotuna wrote:

SJ-Chris wrote:
I would like to understand better what the NORMALtemps are behind the refrigerator while in operation. I assume it is somewhat (or heavily??) dependent on the outside daytime temperature.

-Chris

If I remember correctly the operating temperature may be up to 700 F. (and no that is not a typo). I think I read this at a site that shuts down the unit when it hits about 350 F.

I set my thermostat at 80 f.

"The refrigerator uses three substances: ammonia, hydrogen gas, and water. The cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused. The system is pressurized to the pressure where the boiling point of ammonia is higher than the temperature of the condenser coil (the coil which transfers heat to the air outside the refrigerator, by being hotter than the outside air.) This pressure is typically 14–16 standard atmospheres (1,400–1,600 kPa) at which pressure the dew point of ammonia will be about 35 °C (95 °F)."

I have seen a few different websites mention that the BOILER (which is inside the "chimney" and has insulation around it) operates at around 180*C (which would be about 356*F). But that heat would be contained inside the boiler. Then all the "hot liquid" (...sorry, just using generic terms here) flows through the system, coils, etc and eventually cools. I know that all those coils behind the fridge get warm and/or very hot. This will all create heat behind the refrigerator itself (inside the space where the refrigerator is mounted). I have a roof vent, so the hot air will rise and go out the roof vent, and pull in air at the bottom (at whatever the air temperature is outside).

I'm wondering if anyone knows approximately what sort of temperature this air behind the refrigerator gets during normal operation on say an 80*F afternoon. Is it 100*F? 150*F? I don't imagine it could be hotter than that.

Seeing as how the operation of the system is that the "hot liquid" flowing through these coils needs to cool back down as it flows through these coils, I can certainly see how pushing out, for example, 130*F air and replacing it (from the fan blowing it in at a much more significant rate than with no fan) with 80-90*F air will HELP the liquid cool much easier/faster/lower-temp and thus the refrigerator can have a much easier job (and likely cool the interior of the refrigerator/freezer significantly).

Since I enjoy these sorts of projects/experiments, I think I'll move forward with this project on one of my Class C RVs and when I do I'll be sure to report back with before/after comparisons and data. Will likely take me several weeks as I'm busy with other things at the moment. And I think the best test/comparison will happen when temps are back up to 90*F or more.

-Chris

[2112]

What temperature settings do you have on your fan thermostat?

My factory installed thermal switch attached to the upper cooling fin is set at 130°F.

That switch failed open so I bypassed it with a manual toggle switch inside the lower side cover so I can manually turn the fans on when needed.

Running the two factory installed fans during the hot Texas summer makes a huge difference.

My fridge is mounted in a slide out so the fans are required for proper cooling in summer