Nova Kool RFU 6200 woes.....

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As an update, or admittance to failure, as mentioned before, when this Nova Kool RFU6200 refrigerator/freezer is pulled out from the cabinet it resides in, its temperature gets down to near 29°, which is nice,, but when slid back in it goes up to around 45° depending on the outside condition somewhat, it has been as high as 65°...

So that was obviously a ventilation issue and also diagnosed by Nova Kool, so I installed 4 fans, (all powered by its own dedicated DC circuit breaker to the circled distribution fused bus bar), installed in the following positions -1 DC fan low, at the base of the cabinet, next to a vent, to pull cool air in from the main air conditioned cabin, pointing slightly upward a little, 2 more fans along the lower back wall, pointing at a 45° angle towards the rear coils of the refrigerator, as to help direct the air up, and one slightly more powerful fan about 4 feet higher, in yet another effort to help removing the warm air that can't get out...with all that air circulation the temp climbed back up to mid 40s when repositioned back into its home....uuhhggggView attachment 119923View attachment 119924View attachment 119925

So it turns out it was a boat builder's problem, not a Nova Kool problem.

A company can build a good product, but it can't control what the buyer does with it.
 
Yes, I agree, this NovaKool fridge is working good but when placed back in the environment its housed in, it struggles....

But I did notice today, as the after noon heats up, with the hanging test temp sensor located in the general rear area the fridge is, I seemed to have cross ventilated the airflow enough to be keeping the area temp below 80F, which I think is a good sign...however, and bewildering to me, the fridge temp is climbing. How is that happening?

It pretty much dropped down to 30F while it was out of its hole, within 20 minuets even, (while I installed/relocated a fan), in my attempt to provide a cross flow of air, from a low cool area, to an area opposite area" exhausting the warm air out", basically using the same direction that warm would try to go anyway...just helping it a little....

1. Why when the are surrounding the fridge temp is steady does the internal fridge temp climb?

2. Should the additional fans blow air over the compressor or the coils ,on the rear back of the unit more? (there is already a fan blowing on the compressor but maybe its not enough?)

3. Which one (compressor or coils) is heating up "too much" to keep the fridges internal temp from staying low?
 
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More airflow over the condenser coils will help performance.
 
I added one 50 mAmp fan blowing into the cabinet along with a vent low and another one high and it fixed the problem in our last boat. It didn’t need more than a small amount of air blowing into the cabinet low to help the natural flow of hot air rising to the top. It did blow onto the compressor though. Can’t understand why you have so many fans and still have a problem. When you slide the refer back into the cabinet does it block the airflow? Maybe leave it out 1” and see what happens. That way you know there is room for the hot air to rise. My refer would supply .5 amps for a fan so I could have put 10 of the fans I used in there but one was sufficient.
 
You are governed by the first law of thermodynamics here, whereby in a closed system (the box in which your fridge/freezer unit is stored) heat can neither be created nor destroyed. It just remains. So if you take “heat” out of the fridge, it simply enters the closed space. You need to remove that heat from the closed space in order to improve efficiency. Simply blowing it around is not helpful in the long run. So as others have clearly stated, heat rises so you need to purge the heat at the top of the box using fans that direct it out of the enclosure.

Also, when I talked to Novacool about this problem, the fellow told me to ensure the unit was cranked up to high. These units are meant to have a duty cycle of 100%. It’s not unusual to have them run continuously on hot days. Make sure your battery bank and charging systems are up to the task. It is not a good idea turning these units off to conserve SOC. Finally you need to defrost the fridge on a regular basis.

Jim
 
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I don't turn it off,, and yes, I have 2 fans up high to help exhaust the rising warm air out...both vent to the outside....
 
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Have you looked into one of those thermometers that can use a remote sensor to be left in the cavity behind the fridge while you can read the cavity temp from outside? Without that specific info we are all guessing as are you.

How are the exhaust fans arranged? Are they mounted so there is NOT bypass of the heated air you are trying to exhaust? If not mounted that way the air can simply scoot past the fan and reenter the cavity substantially reducing the fan effectiveness. Just aiming the fan or fans in the general direction of the opening is not good enough.



CatalinaJack:
Agreed that a 12VDC relay which draws about 40 milliamps can be used to power more fans. Even a small relay can control 5 - 10 amps or more easily. Just read the specs. before buying.

Sometimes a car relay for controlling extra, high power floods such as on offroad vehicles can be used effectively.
 
You know I wonder if I didnt make this issue worse.



There was a wooden shelf on the rear wall, about 6 inches deep and the width of the back wall, just above where those 2 fans are shown, (since then they have been removed). but I removed the shelf because here was nothing on it and it looked to me like it wasn't doing anything....


A friend said that it may have been installed specifically to help the fridge by blocking or stopping air in for cooling. I wonder if by me removing it I have crated a larger area now and as a result the air can not be directed as it would have before....


Maybe all I needed was a little more vent action?
 

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JefNDeb,
In case there is a test, I have an American Tug 34.

I have installed a rather large inlet vent.... approx 7X12 inches. I have also taped additional 1/2 inch ridged foam insulation board to top and 2 sides of the fridge box.
Behind my fridge box, I too have a shelf on which the microwave sits. I drilled 2x 3inch hole in the shelf.
I installed an exit vent from the shelf behind the cabinet to vent, in my case, behind the helm seat.
I put in 2 pieces of flexible vent hose from the shelf (plugging up the 3 inch holes in the shelf) to the vent exit. I saw immediate, positive results of a lower inside the fridge box temp.
Now, in the future, I want to install at least one(maybe 2) 3 inch fan that will cycle with the compressor, blowing the heated air out the of the box area to the vent behind the helm chair. Right now, as set up, it is a passive system aka natural convection system.

Why dont I install the fan(s) now?
A. I dont have the fan(s) as of yet (see point D. also)
B. I will need a tech to come out and install them correctly
C. I will need a lengthy wire that will allow me to pull the fridge out without pulling loose the fan.
D. To date, I have been too lazy to move forward on this issue.
E. Finally, I am currently satisfied with the results.
Temp in the box 39.4f
Temp in cabinet behind the fridge, 88F
Outside temp 91F
 
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******Now, in the future, I want to install at least one(maybe 2) 3 inch fan that will cycle with the compressor, blowing the heated air out the of the box area to the vent behind the helm chair.********

Two fans are to me not a good idea. Use one larger fan. I did the 2 x 3" fans years ago and they sounded like a small jet engine. Each fan was by itself dead quiet but the two operating together were NOISY. THey were good quality fans , ball bearings.

There were some harmonics going on that made a racket.

I tried using O rings to isolate them from the wall and each other. NO GOOD.

If you now have two holes then do as I described above, build a light weight box that covers the two exhaust holes and use one larger capacity 4" fan with it blowing into the box. QUIET, barely know it is operating and even then I have to be seated right next to it..
 
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You may be onto something with the shelf removal. Think of it sort of like a chimney. A chimney that is too big will not draw. The heat/air just kind of meanders around instead of forming an updraft.

If you look at old installation manuals for absorption (propane) refrigerators -- they have an actual flame in the back so need a "chimney" of sorts -- they will show that if you have a vertical gap behind the fridge that is more than X" wide, you have to narrow it down in order to get the proper chimney effect. (They had a vent low, and then one on the roof, say in an RV, and it was gap behind the refrigerator between the intake vent and the exhaust vent that needed to be managed for size and not be too deep.)

I've experienced the same thing back in the day with a woodstove chimney. Stove called for around a 5" chimney and someone had used 8" pipe. No draft. I changed the chimney to the correct size.... plenty of draft.

So to me the key is you want good draft (not the same as "maximum space") AND you want to set it up so the incoming air cannot be recycled hot air from the exhaust.

(Obviously when it's sitting in the middle of the room you don't need a chimney/draft because it's not enclosed at all.)
 
One of the true benefits of this forum is the value of everybody sharing their experiences. This is why I am providing an update to my refrigerator delima, otherwise others lose out in their efforts to maybe solve a similar problem they may be having..

As a quick update, we have a AC/DC Nova Kool RFU6200 that early this summer started acting up. Its temp would work its way up to around 46F and so I had to do something to fix that.

The unit will work perfect when pulled out of its cabinet (28-32F) so I and others suspected an obvious rear ventilation issue. So I installed a fan or two, actually 4, (from their own circuit breaker) pulling cooler air in low and exhaust the warm air out up high. But that did nothing to correct the problem. The temp would slowly creep up to around 41-44F in about 90 minuets. So I thought well maybe I am causing more of a problem with too many fans so I installed a DC 6 way fuse block so I can try different fan configs to see but still no go.

I even placed a blanket over the unit, when pulled out, to see what would happen and after about 30 minutes the rear of the fridge (compressor and condenser) was very hot to the touch (the hottest I had ever felt) yet the internal temp was still 30F, which was crazy cause I assumed that was what was happening when slid into the cabinet.

Nova Kool was as helpful as they could be and suggested low refrigerant. They said to pull the unit out, let the temp settle to around 30F and then place a medium size book under the rear of the fridge to tilt it forward some. If the temp started to go up suspect low R134. So I did and the temp went up. Good news I thought.

But when the fridge guy came to check the 134 levels and pressure it was right where it was supposed to be. We leaned the unit forward as before and the pressure and temp began creeping back up.

I just don't understand why this is happening and the fridge guy had never ever seen anything like this.

The temp probe I installed in the area of where the fridge goes in never gets above 78F

These units are $2000 and 22 week lead time.

Do I really need an AC & DC fridge?

Big box stores have the dorm room type AC only refrigerators for less that $300.

I don't know what else to do ...
 

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We have the same fridge, no problem at all.

This is probably nothing but I find strange that in your photos of the top of the compressor, is that rust? Our is over 10 years old and runs 24/7/365 but the compressor is still shiny black. Very strange, maybe send those pictures to Nova Kool.........:thumb:
 
Compressor is branded Danfoss, what looks like a control unit is branded Secop. It took over Danfoss, suggesting the control unit(?)is replaced/newer. Not sure where that takes it, if anywhere.
Agree with rochepoint, compressor looks odd and showing it to NK.
 
Compressor is branded Danfoss, what looks like a control unit is branded Secop. It took over Danfoss, suggesting the control unit(?)is replaced/newer. Not sure where that takes it, if anywhere.

Good catch though. I bought my refrigerator (Danfoss/Secop BD35 compressor) in July 2015. It came with the 101N0500 control unit.

Buddy bought the exact same refrigerator in November 2020, same compressor, and it came with the 101N0510 control unit shown on OP's unit.

Looking it up, the 510 is the direct/newer replacement for the 500. I don't know everything that is different about it (much is the same), but one thing they did is make it so that techs (or owners with Windows computers) could use their Cool4Tool app to make settings and adjustments. Some of the settings can still be made on my "app less" 500 by other means, but there are many more with the Cool4Tool. (It uses the D/I terminal). The 510 will also allow more options for certain digital thermostats.

Anyway, so they are both "equivalent" for each other, just one superseded the other sometime between 2015 and 2020.

That said, your compressor "ball" does look really rusty for a refrigerator that is at least newer than 2016 (unless the control unit was changed). As BruceK said, just an observation.

Just out of curiosity, does it act the same if you run it on shorepower AC? (I see you have the AC capable module; that's the two terminals at the very top.) Not saying I know how this would cause the problem, but just curious as a data point. If the module is working correctly it should switch to AC automatically if it is present.

It is a mystery! Thank you for continuing to update the thread.

Edited to add: If you have any interest in running the Cool4Tool app (maybe to look at or tweak any settings?), it's covered in this Danfoss publication, Chapter 4:

It looks like there is an "error and event log" that records a lot more than you'd find out from the flashing LED. Wonder if there might be a clue there?
 

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PS: I have another question. Pardon me if we talked about this earlier and I've forgotten :blush:

But anyway...

--What is your duty cycle when it's running properly? (in other words ratio of run time to off time)

--How does that change (if it does) when it's struggling vs. when it's doing fine temp wise?

--Also, do you know what size resistor is between the C and T terminal on the control module? (This affects the RPM the compressor runs at; I find I can lower the RPM on mine during cool weather; then in hot weather I put it back up in order to maintain the same duty cycle, which for me is around 40% on/60% off. I think they say 50%/50% is decent.)

Not sure how these things might relate yet, but if you know the answers maybe a theory or idea will begin to form (?)
 
The resistor is the medium speed rating (black heat shrink), the compressor i have never seen cycle off. While I was troubleshooting this, i would leave the unit out of the cabinet during the night, it might have cycled then because as mentioned, it will go down to around 28F when not in its hole, so I would imagine it would then but I cant say Ive seen it.


The unit is a 2005 model so I am pretty sure its the original compressor (as its a closed system and the fridge guy had to add a fitting to check the R134.)


What baffles me is when the unit is sitting out in free space, I placed a thick blanket over the condenser and compressor area, over the entire unit actually, and it really got hot, yet the internal fridge temp remained at 30F....that to me negates any theory that while in its cabinet, poor ventilation is the reason it cannot maintain the low temp....but what do I know, i cant seem to fix this and its been over a month......:facepalm:
 
The resistor is the medium speed rating (black heat shrink), the compressor i have never seen cycle off.

That seems really odd unless your boat lives where your neighbors carry red pitchforks.

I was going to say "unless your boat is in the desert," but I'm in the desert right now (RV), and even at 110ºF ambient I'm still at about 50% duty cycle. I say ambient because the compressor lives in a non-air-conditioned locker that is open to outside air (it's a remote compressor model).

The only thing different from when it's 60º outside is that whereas I was able to shift down to the 2,000 RPM compressor speed then; now I have to run it with the stock 3,000 RPM speed or it will not maintain temp (understandable) (It can also be run at 3,500 RPM which is max allowable from Danfoss.)

***************

This is a bit of a vexing mystery. But I think that the fact that your compressor runs constantly is a clue. That doesn't seem right, and kind of fits with the fact that it never gets the unit down to temp. If it DID get down to temp, then the compressor would cycle off.

Even with the crazy hot ambient temp here, I'm still nowhere near constant running. I'd guess still relatively close to 50% (but at the higher RPM than I run it when cooler out).

Does it also run constantly when you have it out in free air and it CAN maintain temp? (Oh, I see you are not sure on that.)

I might be tempted to throw the 3,500 rpm resistor on there just to see how it changes. Might give you a trend or clue even if you don't keep it that way.

(That would be 1523 ohms/yellow dot.) (Or I think it can be set with Cool4Tool on your 101N0510 if you ever set that up.)
 
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My first reaction to your problem is your fridge enclosure does not allow enough airflow across the heat exchanger coils, which are mounted on the rear of the fridge section, above the compressor, etc. heat builds up in there. That is why the fridge cools better when you withdraw it from the enclosure; better cool airflow across the coils. The RFU-6200 also has a fan mounted in the compressor area that keeps things cooler back there; it is a high failure rate but easy DIY repair. The RFU 6200 is also very sensitive to the amount of refrigerant gas charge. If it is just a tad too high or too low, your fridge performance will suffer. The other two things I think I know about the RFU 6200: (1) If you have an older one, the Power module (102N3031) is no longer available. I am told you can order a 101N0511 and it is easy to modify it so that it works. Older compressors are 4-lead, newer ones are 3-lead. I will attempt to post a pic of the modification next reply. (2) I replaced the door gaskets in order to reduce the frosting inside but it didn't work; I guess the doors may be a bit warped. One more useful piece of info: Novacool is a mom and pop shop. They are located somewhere in BC... if you email or call they will talk to you all day long; not like trying to get hold of Amazon. support@navacool.com
 
I cannot sort-out how to post the pic of the power module modification. I got the info from Robert at San Diego Marine Enterprises, an authorized Novacool distributor. By the way... I decided to replace my 25 year-old RFU-6200 rather than modify the power module. I internalized writing the check for 1700 beans and just said screw it, owning a boat costs a lot of money. THEN I found-out the lead-time on a new one is six months. Not looking forward to living out of a cooler for that long. Not looking forward to tearing-up and modifying the fridge enclosure. Not looking forward to adapting a college dorm or apartment-type fridge for boat-use. Not a lot of marine alternatives, size and dimensions considered. Thoughts welcome...
 
I jumped all over this in an effort to be helpful then I noticed how old the original post was and that all my info had already been posted/replied by others. I'll get the hang of this forum thang... or not.
 
Well as an update and closeout of this post, I trashed unit...bought this for $149...works and fits great...JPEG_20220404_224827_149976619155445228.jpg
 
What is manufacturer and model number? I cannot find one that fits my enclosure... If that one fits yours it ought to fit mine.
 
Hey Jeff, what is the make and model of your new fridge?
 
Novacool RFU 6200

To close the loop: I bought a 120 volt dorm room fridge. Novacool wants 1700 dollars for a replacement... and... there is a six-month lead time. Screw that. I can live without DC power and I don't care about the refrigerant type. The refrigerant in the Novacool (R-34 i bleev) is not flammable, and it allows for the unit to be operated without standing up at a 90 degree angle to the deck when you are pitching and rolling. Well... I thought about it and figured I's take my chances. I've never heard of any apartment refrigerator explosions/fires and I don't get underway in nasty seas. Problem solved. More and more I head out to Ace hardware or Home Depot than West Marine.
 
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