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

[austinjenna]

The best part of this story is that I did not have to go to ER while doing this mod!!

Then you must have been doing it wrong. Please disassemble and try again.

[SJ-Chris]

Blazing Zippers wrote:

The best part of this story is that I did not have to go to ER while doing this mod!!

LOL....that's always a good start!

[Blazing_Zippers]

I glued two 120mm fans to the inside of the black plastic refer grill. They are at an angle so the fans blow upward. I placed a small switch on the outside of the grill to turn the fans off/on.
I have noticed an improvement in the refer temps.
I had one fan, the switch, and had to buy one fan for $13.00.
The best part of this story is that I did not have to go to ER while doing this mod!!

[pianotuna]

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)."

[JaxDad]

I added a rooftop self-powered vent fan to the top of my C many moons ago, it uses no power and is nearly silent.

They are often used on tradesman’s vans, especially ones that carry anything flammable (torches, liquids, etc) in the back. You’ve probably seen one and just didn’t realize what it was, they look like a child’s spinning top. The principle is, as you drive, or even a light breeze blows, the exposed spinning top turns, this in turn spins a smaller fan down below the roof which forces air up and out through the top spinner.

It works very well, and uses zero electricity.

https://www.flettner.co.uk/van-roof-vents/

Not the same make as the one I used, but the first example I found of a similar product.

[SJ-Chris]

pianotuna wrote:

SJ-Chris wrote:
Does anyone have any "before and after" data points or personal observations after having added such a fan?

Thanks!
Chris

Yes.

Cool down from ambient without fans 4.5 hours to first cycle

Cool down from ambient with fans 3 hours to first cycle.

My twin computer fans are in a mask at the top of the chimney. They are thermostatically controlled.

This limits air flow in colder weather.

I do have a thermocube and a 40 watt bulb for freezing temperatures.

pianotuna (and others with fans): What temperature settings do you have on your fan thermostat? What does the ambient outside temperature need to be before your refrigerator vent fan actually turns on? Does the fan only turn on on hot days? Warm days? Or even on cool days?

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. Say for example on a 70 or 80 degree F afternoon, what temperature does the space behind the refrigerator get? Is it just slightly warmer than outside ambient air temperature? Or is it 20, 30, 50 or more degrees hotter than outside ambient air temperature? I'm trying to understand what the temperature difference is between ambient outside temps and the temp behind the refrigerator. I suppose if the temperature behind the refrigerator gets 40 or 50 degrees hotter than outside ambient air temperatures then blowing in more outside air will definitely help cool that air behind the refrigerator significantly and make a fan worthwhile.

Is there any downside to the refrigerator's operation that could happen by adding a fan to help cool behind the refrigerator? Is it possible to blow TOO MUCH air across the cooling unit and out the top vent? I see some inexpensive fan/blowers online that push ~45CMF. This could be mounted to the side exterior vent and blow up the back of the refrigerator towards the roof vent.

-Chris

[stripit]

When we full timed in a Mobile Suites 5th wheel I installed 2 fans, one at the bottom area and one up top at the factory installed vent. This way I was sucking hot air and helping it extract out the top. We found before that if we were parked where the kitchen/refridge side was exposed to the direct sunlight and it got hot, the fridge was not able to keep the correct temps. I could remove the fridge exterior acess panel and either plug in or unplug as the need arose. I bought 2 square box fans about 4 inches across and they fit very well and had no noise we could ever hear.

[pianotuna]

SJ-Chris wrote:
Question: What does "in a mask" mean? Thanks!

-Chris

Think of a floor fan. There is nothing other than the grill work.

Now put that fan in a wall. The wall acts as a mask.

[SJ-Chris]

pianotuna wrote:

SJ-Chris wrote:
Does anyone have any "before and after" data points or personal observations after having added such a fan?

Thanks!
Chris

Yes.

Cool down from ambient without fans 4.5 hours to first cycle

Cool down from ambient with fans 3 hours to first cycle.

My twin computer fans are in a mask at the top of the chimney. They are thermostatically controlled.

This limits air flow in colder weather.

I do have a thermocube and a 40 watt bulb for freezing temperatures.

Cools 33% faster....excellent data point!

Question: What does "in a mask" mean? Thanks!

-Chris

[SJ-Chris]

Fisherman wrote:
I'm not in the same temperature zone as you are but without a doubt adding a 4 inch fan at the upper vent made a fair bit of difference. It was a 3 speed fan and I was lucky enough to have 2 unused spade terminals on the back of the fridge made for this, on all but the hottest days I had it on the lowest speed, 90+F days I upped it to med or high as required and wouldn't believe the heat coming out of the vent. It definitely dropped the interior fridge temps and sped up the cooling process by about 1/2 the time. I don't know what the dB rating was but I could barely hear it at night during quiet times. I don't know what the brand name was, just 12DV DC with a 3 speed switch.

Cooling in 1/2 the time seems very worthwhile. Thanks for the data point!

[Lwiddis]

An interior fan is all I’ve needed.

[pianotuna]

SJ-Chris wrote:
Does anyone have any "before and after" data points or personal observations after having added such a fan?

Thanks!
Chris

Yes.

Cool down from ambient without fans 4.5 hours to first cycle

Cool down from ambient with fans 3 hours to first cycle.

My twin computer fans are in a mask at the top of the chimney. They are thermostatically controlled.

This limits air flow in colder weather.

I do have a thermocube and a 40 watt bulb for freezing temperatures.

[enblethen]

I would check for clearance between outside wall of rig and the cooling fins. It should be less than an inch. By reducing the clearance as indicated in installation manual more air would move through the cooling unit coils increasing the efficiency.

[Tvov]

Our frig always seems to work better when the daytime temperatures are hotter. My wife has mentioned that too, so I don't think it is just me imagining it. Our TT frig has side and roof vents, so I assume the hot air vents itself out.

I am not sure an exterior cooling fan would make much of a difference.

What I have heard a lot of people do is put a fan inside the frig to help even out the cooling.

[toedtoes]

My motorhome never needed it. The heat easily rose up the vent and out. The fridge never had reduced cooling even in high temps.

With my trailer, it is vented out the side. The fridge cooling capabilities are significantly reduced in high temps. The fans are absolutely required - I also put a reflective window sheet on the wall below the vent to reduce the external heat.

If you have a significant difference in the fridge's cooling capabilities depending on external temps, then adding the fan may help. If there is no difference, then the fan is unnecessary.