Nova Kool RFU 6200 woes.....

[jefndeb]

We have a Nova Kool 6200 with a new danfoss AC/DC controller, new door seal and new thermostat. Temp gets up to 54f during the heat of the day which is not good....but the freezer is a freezing 17f...???

I have added a fan in the upper cavity where it is enclosed, pulling the hotter air out, but when the unit is pulled out of its normal position it gets down to a normal 36f but when repositioned it goes way up to around 55f...what the heck???

Any ideas why?...can it realy lget that hot back there to cause this???

Installled in a Mainship 40

Comments welcome ....

Jeff

 

[DDW]

Stick a thermometer back there and see. The problem with a Nova Kool or any similar fridge mounted in a cabinet is two fold: any temperature rise in the cavity warms the condenser and 5 sides (of the six) on the box. All the energy you are dumping into that compressor is going into heat back there. 6A x 12V is almost like an old style 100W bulb - pretty warm. With a fan ventilating the box, you still need to measure a few places and see how high above ambient the back of the box is.

 

[Comodave]

Does the cabinet have an air intake down low and an exit vent up high? If not then add one of each. I put the fan on the intake vent blowing air into the cabinet and it made a big difference.

 

[OldDan1943]

Questions on your NovaKool RFU6200. (I have a RFU8000DC 12vt only)
Every now and then, there is a great interest and number of questions on "How to improve the effency of the NovaKool."
Your unit AC/DC. Reacts the same on AC?
It is stuffed into an almost non-ventilated cabinet?
How often do you defrost the fridge and freezer? Ice on the inside coils insulates and therefore reduces the cooling capability. It is IMO, it is the humidity inside the box that allows for ice build up. (small box, doesn't take much humidity to increase the ice build up) The temp (ice build up) between the fridge and freezer boxes is because you open the fridge more often than you open the freezer box. That's a bit confusing but, unless I spend write another 200 words, please just accept it.

You have started out in the right direction. new door seal. I think you replaced the thermostat 'just because'.

So many things can be done to 'improve' the NovaKool but remember, it is not a "real" home frost-free type fridge.
You also have to get the heated air out from behind the unit. Put an additional vent inlet grill lined up approximately with the compressor part. Then, add an additional vent up high to get the heated air out. Consider adding an additional fan in the compressor area to force the heated air out from the compressor area and out the additional vent. You may have to add some duct work to direct the heat from the compressor area out the exit vent.
Add 1/2 to 3/4 foam insulation board on the 2 sides and top.
There is 'talk' about the benefits of keeping the tray, under the coil, in or out, you decide based upon your observation. Removing the tray should allow for greater dispersal of the cooled air. Also, additional talk about relocating the temperature sensing bulb from the coil area to the side of the fridge box.

One other item will help. A Stainless Lobster. You can do your research on that and make your own decision. I have one because it forces a 'timed' defrost (shut down) cycle and an internal fan.

That about covers all the things I have done to my NovaKool except, I have yet to install the additional fan in the compressor area.

Keys to note; Reducing the open door time will reduce humidity and the ice build.
Reduce the humidity in the box. Good luck on that one.
Increase the ventilation behind the box. Get air in and heated area out.
Everything recommended, IMO, is an incremental improvement.
Keep me/us informed of your progress.

 

[jefndeb]

Thanks for the suggestions,

Yes it has a lower air vent and an upper or mid vent. I installed a fan on the upper vent (next to the coffee maker) in hopes to pull cool inside air from the lower vent.

But in pulling the unit in and out i noted that the area behind the fridge is open to a much larger area where the engine air intake is meaning that my theory of the airflow is flawed, probably just pulling from the path of least resistance and as you can probably tell when the unit is fully slid in that lower vent is partially blocked...

Time for some airflow adjustments...View attachment 119631

 

[OldDan1943]

Strange way to vent in.
More airflow in and out. Maybe more fans too?
Because the lower vent is blocked when the fridge is in the cabinet, double the size of the lower vent????
Expand the 'in' vent flush to the oven cabinet as you double it in size???

 

[DDW]

I'd agree that it isn't just airflow, the airflow must sweep the area of the condenser coils. You'd also like the sides, back, and bottom to be near ambient. There are bluetooth recording thermometers cheaply available on Amazon, two or three of these can be taped in various locations and record for a day to see what you've really got, with the refer in and out of the box. You may be able to put in some light plywood deflectors on the vents you have to improve the flow.

 

[OldDan1943]

Milt Baker (former owner of an AT34) made the observation, 'The NovaKool RFU8000 maybe good for the PNW but, it is marginal for the east coast.'
I agree. All we can do is make improvement we know will improve the unit and defrost as necessary.
Now, if we could figure out a way to reduce the humidity inside the main box we would not have to defrost as much.
I have been known to leave the fridge on when I leave the boat for a couple of month. When I return, there is no need to defrost because I am not there to open either of the fridge's doors.

 

[rslifkin]

On my RFU9000, adding some more insulation to the box and changing up the fan setup to get more air moving across the condenser, as well as adding a small fan to move a little bit more air across the evaporator in the fridge section made a big difference in hot weather performance. It still starts to struggle a little if it gets much above 85 degrees in the cabin, but by the time it can't keep up we're well into the point where I'm miserable and will have turned the A/C on to cool things down.

 

[OldDan1943]

Prior to the installation of all the above improvements, for years I had a small D cell battery fan inside the main box. Seem to improve the efficiency somewhat. Once a year I would change the battery until the fan crapped out. I could never find a replacement fan.

 

[Comodave]

Your lower intake vent is pretty useless since it is blocked by the side of the unit. Our last boat had one just like that. I added a vent that had direct access to the compressor area. Put the fan on that vent blowing into the compressor. The fridges’ efficiency improved dramatically. You say that it works fine when pulled out of the cabinet, so the cabinet is your problem.

 

[Comodave]

Prior to the installation of all the above improvements, for years I had a small D cell battery fan inside the main box. Seem to improve the efficiency somewhat. Once a year I would change the battery until the fan crapped out. I could never find a replacement fan.

We used one of those also just to circulate the air in the fridge box. You can get them at RV supply stores. They do help quite a bit.

 

[FF]

"Prior to the installation of all the above improvements, for years I had a small D cell battery fan inside the main box. Seem to improve the efficiency somewhat. Once a year I would change the battery until the fan crapped out.

I could never find a replacement fan."

Perhaps,

https://www.amazon.com/Beech-Lane-M...214452839&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdv

 

[Dougcole]

Thanks for posting Jeff, I am watching with interest. I also tried putting a fan on the lower vent and it didn't seem to do much of anything. I wired it into the F terminal on the controler and it just ran non stop. It was a little bit loud, so I ended up disconnecting it.


I think it would be pretty difficult to add insulation to the sides of the box unless you do some cutting of the cabinetry. Mine is a really tight fit in the opening and there is not much wiggle room for cutting. There is a ton of space behind the fridge though.



What do you think about cutting another vent up high in the back of the box and putting an exit fan there? Maybe it is too close to the fiberglass cabin side?


Doug

 

[OldDan1943]

These are supposed to be very quiet ballbearing fans.

https://www.acinfinity.com/quiet-usb-fans/

IMO, adding another vent up top will be of no benefit. You have to establish air flow from the compressor area. Adding another vent may end up short cycling what air flow you do have.

 

[rwidman]

Nova Kool has a very good and very responsive customer service staff. Give them a call and describe your problem. I'm sure they can help you fix the problem and probably without any modifications.

 

[jefndeb]

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....uuhhgggg

 

[Comodave]

I don’t remember if you have a high vent to let the hot air out or not. If not then you probably need to find a way to make a vent up high.

 

[OldDan1943]

If you can figure a way to vent the hot air out near the top, you will complain the ice cream is too hard to eat.

The below 3 things are suggestions to try one at a time. Try one, if the effect is not as you want, return it back to the original configuration and try the next etc.
Do all MS400 have the main breaker panels located in the galley?
What is the item mounted about the breaker panels?
1. Can you pull that out and see the effect on the air flow and fridge temp?
2. Take the measurements between the TV and the fwd edge of the cabinet then, either start your internet search or have a custom vent made.
3. What is outside of the back wall where you have mounted the fans? You may have an opportunity to use a hole saw to vent out into the 'great unknown' behind the fridge. (turn the fans around to force the air out the back)

 

[jefndeb]

Yes, if you sit in the area the fridge normally sits, you can look up and can see an opening where basically a flybridge speaker is mounted, my plan C was to remove the speaker, and using that hole for access, cut a 3 inch hole and mount yet another fan there, again, an effort to provide a path for the air to flow out...wife says to tap into the AC ducting and route conditioned air back there.....may be plan D....what part of the refrigerator needs the airflow access more?
The compressor, which already has a fan, or the coils on the back of the unit?..is that the condensor?

 

[Comodave]

The hot air needs an exit. All the fans blowing into the cabinet without an exit may not do much. We had a problem on a previous boat with the fridge not cooling. I added a low and high vent with a fan blowing into the low vent. The hot air was pushed out the high vent. Problem solved.

 

[Frosty]

Another tip (which I can't really tell if you already have implemented or not) is that you want to make it so the compressor area *cannot* suck [back] in any of the warm exhaust air. It should only have access to cool "fresh" air (or as cool as possible).

Your cabinet shape is totally different than mine, but I used some thin metal and some stiff foam to make a septum so that never the twain shall meet. My compressor cannot suck in any of the exhaust air, which is hotter than ambient by a good bit.

Another thought (which is more of a fix for if you cannot get the temp any lower in the cabinet) would be to put whatever resistor gives you the highest possible compressor RPM. In the case of my BD35 that's 3,500 rpm (the lowest allowed is 2,000 so that gives you an idea of the range).

(My refrigerator came with a resistor that set it at 3,000 rpm. My refrigerator box is one of the largest that takes the BD35 compressor. What I did was create a two way switch. One way runs it at 2,000 rpm, which is most efficient and works 90% of the time. The other way uses the resistor and runs it at 3,000 rpm, which I use only when it's very hot out (over about 95ºF)

 

[OldDan1943]

Yes, if you sit in the area the fridge normally sits, you can look up and can see an opening where basically a flybridge speaker is mounted, my plan C was to remove the speaker, and using that hole for access, cut a 3 inch hole and mount yet another fan there, again, an effort to provide a path for the air to flow out...wife says to tap into the AC ducting and route conditioned air back there.....may be plan D....what part of the refrigerator needs the airflow access more?
The compressor, which already has a fan, or the coils on the back of the unit?..is that the condensor?

I suggest you have more than enough fans now. You just need to provide an exit for the heated air.
What part needs it more? I think once you establish a fan assisted air flow out a well defined exit, you will see at least another 3-5 degree decrease in the main box. IMO, feeble as it may be, you dont need a massive air flow, just enough to remove most of the heat build up. The fan will 'teach' or encourage the airflow out the exit. Draw from the compressor area out the exit.

I cannot tell you how much I hate 'hidden fuses.' If a fuse blows, I do not want/need to disassemble the boat to get to the blown fuse.

 

[C lectric]

Agreed that the warmed air MUST be forced out a vent hopefully ABOVE the fridge or at the very least above the cooling cools as that is where the heat is disposed or rejected.
Blowing the air around without venting that heated air will do little to cool the cavity the fridge sits in.

 

[jefndeb]

Still fighting this issue, I installed yet another fan way up top that exhausts the air to the outside and another fan to assist the existing fan that blows on the compressor...same results, fridge temp climbs up to 45°....

Again, as mentioned before, when the unit is pulled out of its cabinet its temp goes down to 29°...obviously a ventilation issue..

Recap, I have 1 fan down low pulling cool air in, one fan helping the existing novakool compressor fan, one fan 2 feet above pulling warm air upwards and the one I added today in an attempt to complete the flow out.

The air coming out onbthe upper fan feels a little warm, which is good news and the temp sensor i have installed behind the fridge to monitor has gone up to 83° during the peak outside today...ill keep fighting the fight....

 

[OldDan1943]

Can you put a fan closer to or at the exit vent so you are drawing the air through the inlet and out the exit vent?

Remember, I have a Stainless Lobster installed.

I do not have a fan at the lower vent near the compressor. Rather than adding the fan there, I will eventually add one at the exit vent.

Inside the fridge box 40f
Back of fridge box 86f
Room temp 73F (night time)

I guess I need to defrost the main box real soon. I have some ice build up and as we know, ice reduces the efficiency of the 'compressor plant'.

In the mornings, the inside the box temp will be about 37F.

 

[C lectric]

Still fighting this issue, I installed yet another fan way up top that exhausts the air to the outside and another fan to assist the existing fan that blows on the compressor...same results, fridge temp climbs up to 45°....

Again, as mentioned before, when the unit is pulled out of its cabinet its temp goes down to 29°...obviously a ventilation issue..

Recap, I have 1 fan down low pulling cool air in, one fan helping the existing novakool compressor fan, one fan 2 feet above pulling warm air upwards and the one I added today in an attempt to complete the flow out.

The air coming out onbthe upper fan feels a little warm, which is good news and the temp sensor i have installed behind the fridge to monitor has gone up to 83° during the peak outside today...ill keep fighting the fight....

I see you installed a fan and vent at the top. Have you improved the air entry at the bottom? Air MUST be able to enter easily at the bottom.

I arranged mine so the air enters at the bottom, rises up the back over the cooling coils and then, at the top, is exhausted to the outside of the cavity.
The air entry at the bottom is also forced to travel to just below the coils so it has to rise over the coils.

Without ensuring that there is good air entry at the bottom then it cannot be as effective as needed.


Have you bought an electronic thermometer? THey are quite cheap and an extra sensor can be purchased and left in the fridge cavity to monitor the cavity temp. THe talk between them is radio signals. THey work quite well.

 

[C lectric]

Still fighting this issue, I installed yet another fan way up top that exhausts the air to the outside and another fan to assist the existing fan that blows on the compressor...same results, fridge temp climbs up to 45°....

Again, as mentioned before, when the unit is pulled out of its cabinet its temp goes down to 29°...obviously a ventilation issue..

Recap, I have 1 fan down low pulling cool air in, one fan helping the existing novakool compressor fan, one fan 2 feet above pulling warm air upwards and the one I added today in an attempt to complete the flow out.

The air coming out onbthe upper fan feels a little warm, which is good news and the temp sensor i have installed behind the fridge to monitor has gone up to 83° during the peak outside today...ill keep fighting the fight....

I see you installed a fan and vent at the top. Have you improved the air entry at the bottom? Air MUST be able to enter easily at the bottom.

I arranged mine so the air enters at the bottom, rises up the back over the cooling coils and then, at the top, is exhausted to the outside of the cavity.
The air entry at the bottom is also forced to travel to just below the coils so it has to rise over the coils.

Without ensuring that there is good air entry at the bottom then it cannot be as effective as needed.

After a bit of reread the base temp of the incoming air cannot be less than the air outside the box. But there must be enough FLOW over the coils to carry the heat away.

So what are the fans capacities in CFM? Specs. should tell you.

From the entry to the exit what are the CFM specs. Some times just adding more fans may not be enough without some direction to the air flow AND the volumn moved AND the positioning of the smallest to the largest fan.


*******one fan 2 feet above pulling warm air upwards and the one I added today in an attempt to complete the flow out.******** Is the out fan actually mounted to the outlet or is it just nearby aimed at the outlet. The latter will be no where near as effective as a fan mounted over and covering the exhaust port.

My own example. When I went from two smaller 3" fans to one 4" fan the new 4" fan did not cover the two smaller holes.
I built a light weight , 1/4" ply box to cover the whole of the two openings and mounted the 4" covering the one hole into the box.

 

[catalinajack]

Jefndeb, or others who may know, how are those extra fans turned on and off? The Danfoss compressor modules do have the ability to power one extra low amp fan but how does one power a higher CFM fan that is controlled by the compressor module? I have a pair of Vitrifrigo fridges that are contained in a custom-built cabinet. I allowed a 1.5 inch space underneath the floor for air flow in. There are large vents on the sides of the cabinet high up. I installed low amp fans, .5 amp as I remember, that operate whenever the compressor runs. The fridges keep cool down to 35 degrees when the outside temp is as high as 90 degrees and down to 40 degrees when the outside temp above 90.

I ask because I have always wanted to install higher CFM fans and have not been able to figure out how to get them to power on and off automatically.

The pictures - the fridges there are not the Vitrifrigos I installed later. They were household fridges that did not keep cool. The cooling coils in those damn things were in the side panels that got no airflow, something that I did not understand when I built the cabinet. I decided to replace them when one day I pulled them out and found the metal sides almost too hot to touch.

The Vitrifrigos, of course, have the cooling in the rear. Before I installed them I drilled three large holes across the back of the floor to allow direct air flow from under the floor through the bottom front. I installed the extra fans at the top of the vents. If you look closely, you will see a 120VAC outlet and a 12VDC power supply. They are both circuit breaker protected dedicated circuits. I chose 12VDC-only fridges and use the 120VAC circuit as an additional outlet for other purposes.

 

[rslifkin]

You can have the Danfoss module trigger a relay and use that to power the fans if you're over the power limit for the controller.