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Discussion Starter · #1 ·
I'm betting I am one of many here who have a Dometic/Thetford/Norcold 12v and 120v front opening refrigerators. Mine is a 2.7cu ft NR751. It is a nice unit, easy to mount, cools great and even in 80+ temperatures it seems to use a modest amount of power. My question is why does it have a fan? I see the fan is used to pull in air from the lower vent on the left side and exhaust the warmed air out the right side also under the unit. The unit could easily have an upper vent and allow a chimney effect to do the cooling and eliminate the fan. I can hear the fan not the compressor and it is irritating and seems unnecessary if they had just let the coils vent out the back of the cabinet.
Anyone with expertise and/or experience with these units that could suggest a way to eliminate the fan? No other electric refrigerator I have ever had used a fan outside. Are there ways to slow or quiet the fan? Just remove it and open the back to air? I hate to break it by doing something stupid. Oh- and no, I can't just ignore it!
 

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It has a Danfoss type compressor so if you can get to the control unit on the compressor you can disconnect the wires that power the fan.

Try that and see if the noise is less and the run time doesn't increase. I don't how hard it is going to be to allow the warm air vent upwards.

I have had 2 12volt compressor refrigerators. One with a fan and my current one without a fan. I haven't noticed any difference in their cooling or run time.

I have an hour meter connected to the fan terminals on the compressor control unit so I can track the run time. Total run time is usually 3-4 hours a day. I did add extra insulation around both of the units.
 

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RD,

I have not purchased a my fridge yet but it will also be a 12/120v version (probably will buy a Novacool as they make them in my backyard), so thank you for the heads up:) any amount of noise in these small boxes can wear you down.

You may want to check out Orton's (Dave) build over on the Transit and Sprinter forums. Dave is bringing in fresh air through the floor that passes through the fridge cabinet. The vent serves double duty in that it helps cool the fridge and provides a fresh air intake for his roof vent.

I will be installing two fresh air intake vents in the floor to feed our multiple vents and sky lights (we have three fir kids;).

I did not think to much about Orton's desire to send fresh air past his fridge, but now that you mention the fan noise I'm going to rethink the positioning of my vents.

Cheers,

Dave
 

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Discussion Starter · #4 ·
I contacted Norcold asking if I could vent the refrigerator instead of running the fan and got this response:

"I'm sorry that you are bothered by the sound of the fan. But without this fan running with the compressor, your unit is subject to over heat and cause cooling issues. This a stand alone fridge like your home fridge, so it does not require outside venting.

Thank You

Vincent
Consumer Service
Thetford Corp/Norcold Inc "

This was just what I expected but doesn't really answer the question "CAN I vent the refrigerator and eliminate the fan?"
 

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But without this fan running with the compressor, your unit is subject to over heat and cause cooling issues.
I will tell you that you "CAN" run the refrigerator without the fan. It is a free country.
BUT, as an old HVACR tech I will say it will overheat, and perform poorly and will be subject to premature compressor failure. Refrigeration condensers are sized based on desired capacity of the evaporator coil and refrigerant type. Compressor cooling is partially done by returning cooled refrigerant gas from the evaporator. Without the proper cooling for the compressor you start breaking down the oil in the system (refrigeration oil becomes acidic when it breaks down), then the bearings in the compressor or the insulation on the windings fail.
Sometimes on smaller units the fan is double shafted and powers both the evaporator and condenser coils. Removing heat from the gas and returning it to liquid is a required part of the refrigeration cycle. No condensing, no cooling.

But if you have room you can duct air to the fan intake and move the sound elsewhere, like inside a cabinet, you just need to be aware that the length of the duct will have an effect on the cooling also. Just a PVC 90 could be enough to point the sound elsewhere.
 

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Discussion Starter · #6 ·
I marvel at the knowledge and expertise here. Thanks Karl I understand better and will work on sound attenuation instead of fan removal! It is a nuisance really and I would have bought another unit if I had known but I am sleeping fine with it coming on and going off and the refrigerator is quiet otherwise. Right after it arrived I tested it out on a shelf in my garage and noticed the fan right away but felt it would be quieter in its cabinet. Since it pulls air from underneath and exhausts it underneath there seems little way to cut the noise. I'll think about it and perhaps something will occur. I wonder if a similarly rated fan (CFM) might be found that is nearer silent. Some computers seem to have them. It looks like a 4" square by 1" thick standard box fan.
 

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The cabinet may be amplifying the sound just like a speaker cabinet. So look at isolating the fridge from the cabinet rubber feet or bumpers make sure the fan is firmly attached maybe add rubber idolater's this should take care of mechanical noise. For wind noise try acoustic insulation maybe some foam like this.
http://www.thefoamfactory.com/acousticfoam/acousticfoam.html
If you search for sound deadening foam you may find what you need.
 

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The Danfoss BD35F compressor is bullet-proof, will work for many many years in tropical climates at almost 100% duty cycle, say on a boat where water temperatures are 80°+ and hull interior temperatures just climb way higher than that. What is not bulletproof is the inverter/control module that takes 12/24VDC and steps it up to 300+VDC to efficiently drive the compressor.

Long term heat is the enemy of the electronics. The control module is produced by Danfoss & I doubt they'd allow cost-cutting by inserting lower-grade low cost components on request from Dometic/Norcold that would require a cooling fan merely to survive their whole two year warranty.

From your owner's manual: (translation: warranty lawyers covering all bases)

Operating the refrigerator in high ambient temperatures can over heat the cooling unit and cause premature failure of the compressor. To protect the cooling unit from over heating, the refrigerator will automatically shut-off when the temperature of the refrigerator power module is higher than approximately 100° C (212°F). The refrigerator will restart when the temperature of the refrigerator power module is lower than approximately 80°C (176° F).
I'd imagine their warranty design covers extremes... So you're in South Florida and want ice for your beverages of choice in the heat of the day, their refrigerator is on the south side of your nearly uninsulated RV and air stagnates and super-heats the equipment area just inside the wall and cooks the control module. Same would go for Afghanistan or Iraq, etc. etc. so a 24x7 cooling fan might make sense there.

Okay, fine, you're not in Sub Saharan Africa, so... IF you can ensure a good draft occurs while the unit is running and cooler floor-level air gets smoke-stacked across the compressor (warm air venting pulls cool air in behind it) & the cooling modules utility space behind the refrigerator is well insulated from daily sun heating then you're likely to 'get away' with clipping the fan wires. A better choice might be all the above PLUS putting a bi-metal temperature switch on the fan wires to power it up when the running temperature exceeds 135°F.

Keeping the unit clean by design and maintenance - no lint, cooking fume residue, low or no dust/pollen build up, no spider webs or mouse nests - is key to a Danfoss units long life. Many rough service (fanless) units make 10 or 12 years and more before something lets go in the control module.

As for outdoor air venting - between inviting fumes, vermin/bugs and infinite humidity & dirt into that utility area AND likely drawing in sun-heated air off pavement or ground during the heat of the day it likely would not be very beneficial. Remember also the vent likely will continue to draw air in 24x7 in fair or foul weather. I've had two propane powered ammonia cycle refrigerators that must draw a draft in from under a trailer floor and they get filthy & begin to corrode pretty rapidly. BUT having the whole vans interior get some air exchange (filtered?) to shunt sun heated air outside ASAP could be a good idea, so no to venting the DanFoss unit and yes to a cooler van interior.
 

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Discussion Starter · #10 ·
Zoomyn says:
"A better choice might be all the above PLUS putting a bi-metal temperature switch on the fan wires to power it up when the running temperature exceeds 135°F."

I really like that idea. Let the control board turn on the fan circuit but let the normally open 135 degree or so thermostat close the fan circuit when it is really needed! Then work on the acoustics and natural venting. I have a couple of more urgent projects so it will be a bit but I'm liking the ideas!
 
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