NovaKool RFU 6200 Fridge Resister option?

Hello,

We have a 2005 NovaKool RFU6200 AC/DC Refrigerator/Freezer in our Maniship 40.

The freezer part works great but the fridge part struggles to keep the temp below 48...we have the thermostat adjusted full cold...

We have pulled it out and checked the fan, wires etc...it all looks good,,,I have seen it go down to 37F but then it would just decide to go back to 50F...

I read in the manual that there is an optional resister that can be installed that can speed up the compressor. I am not sure if we have it installed, (I will have a look this weekend), but I thought I would ask if anybody knows if this would help or not.

Thanks in advance,
Jeff

The resistor is installed in series with the wire from the thermostat. It controls the speed of the compressor. I think the manual has a list of values but it's on the boat. When I first ran across this I contacted NovaKool and they not only told me what value to use but sent me a resistor with the connectors attached at both ends.
Give them a try.

ok, thanks...but will that fix my issue?
Did you have the same problem?
Jeff

The unit cooled but the compressor ran continuously. Here is a copy of an email from NovaKool:
>>
Hello Bob
Sorry they didn’t get to you

For medium speed a 500 ohm resistor and for the fastest speed a 1500 ohm resistor
The wattage doesn’t matter as the circuit simply looks for the ohm value (no amperage there)

If you shot me your address we can try again!

Best regards
Sean
604 523 6515
<<
They mailed the resistors to the marina but we never received them. They remailed them again after we got home. The 500 ohm seemed to do the job.

Replace the fridge door seal!!!!
I have a NovaKool fridge RFU 8000DC 12vt 6.8CuFt

Increase the air flow in and out of the cabinet (where you keep the fridge). Maybe an extra fan in the compressor area.
Consider, while you have the fridge out, adding 1/2 inch foam insulation boards on top and 2 sides. Tape together with silver tape.
I replaced the standard thermostat with a "Stainless lobster" It gives you a digital read out of a few parameter such as temp, humidity, compressor run time plus a user defined defrost time. It is the humidity that messes with the ice buildup.
I have pulled out the plastic tray under the fridge coils to allow for greater air circulation.
Yes, I still defrost every 2-3 weeks.

You can adjust the compressor speed but if the fridge cannot get rid of the heat removed then it will run and run and not cool.

Many fridges need/must have at the very least a good sized vent at the top of the cavity and a good size air entry hole at or very near the bottom of the cavity. The best is both vents are at the back so the cooling tubes get the air circulation across them. With out that it cannot cool since the heat collected is not being disposed of.

Years ago I installed a small 12-14 Vdc fan arranged so it vacated the fridge cavity at the top. I ran into the same trouble you seem to be having. My then fridge was running and running. I set mine to exhaust to the outside, but exhaust to the inside would work also. But more than likely you need to set up a forced exhaust with a small fan.

Nova Cools use the BD35 or BD50 compressors by Danfoss. THose control boxes provide for a fan drive up to 0,5A [500 milliamps] at 12V. My fan draws about 180 milliamps and is a 4" case. Then the fan runs only when the fridge runs which is all that is needed to cool the unit.
Muffin or also known as computer types they are quiet. I can barely hear mine and I sit reading right next to it.

Before I forget do NOT get a sleeve bearing type, Get a BALL bearing type. Quieter usually by a lot and longer lived.

If you don't provide for proper ventilation the faster running compressor will not change much as it still may not be able to get rid of the heat in the cavity that it collects from the fridge interior.

A last comment is be sure there is not something actually wrong by pulling it out, setting it on the floor and trying it that way to see if it cools and starts cycling.

Mine is also a Nova Cool about 6 yrs old.

I had trouble with my refer cooling. I added a vent low in the cabinet and at the top of the cabinet. I added a fan that draws .05 amps pushing air into the cabinet at the bottom. The refer can drive a .5 amp fan so the power consumption is well within the specs. The refer cool really well now. This is the fan I bought from Amazon.

Noctua NF-F12 PWM, Premium Quiet Fan, 4-Pin (120mm, Brown)

Comodave's fan would do the job. Very similar to the one I used.

C lectric said:

Comodave's fan would do the job. Very similar to the one I used.

Click to expand...

And it is really quiet too. I bought another one to evacuate heat from the compartment that will house my new LiFePO4 batteries since they will shutdown if they go over 111 degrees. And the fan draws so little I am just going to turn it on in the spring and off in the fall.

Yes, the Danfoss compressor has a provision to drive a fan of up to .05 amps. My two fridges are set up that way and they keep cold during the summer. But, what if one would want to use a fan that draws more current to get higher CFM? Could one use that circuit to drive a relay so that power to the fan is not taken from the compressor? My fridges are 12-volt only so I have ready access to independent 12VDC. Would a common automotive relay work?

For folks looking for a reefer , there are some units that vent out the warmed air into the cabin.


These do not require a chimney or vent which can be a PIA to engineer and install.

On my American Tug, the microwave sits above the NovaKool on a wooden shelf.
Some owners', including myself, put 2 3" holes in the shelf, a vent from the fridge cabinet via flexible hose and out the back of the microwave cabinet to a collector, venting out the back behind the helm seat. Put a small 5 inch box fan in the compressor compartment and a 3 inch fan pushing heated air out one of the 2 3inch vents.
I also installed a larger vent into the compressor area.
I also had a rust problem on the surface between the main box door and the freezer box doors. Got rid of the rust down to the bare metal and repainted black with Rustroium paint.

Remember, the ice build up is the result of a high humidity inside the main fridge box. The freezer compartment..... defrost about every 2 months if the ice build 'suggests'.

catalinajack said:

Yes, the Danfoss compressor has a provision to drive a fan of up to .05 amps. My two fridges are set up that way and they keep cold during the summer. But, what if one would want to use a fan that draws more current to get higher CFM? Could one use that circuit to drive a relay so that power to the fan is not taken from the compressor? My fridges are 12-volt only so I have ready access to independent 12VDC. Would a common automotive relay work?

Click to expand...

Are you sure it is .05 and not .5 amps? Most that I have seen are .5 amp. But if it is indeed .05 then the fan I referred to above is .05 amp somit would work.

ok, looks like the most likely cause is the area where the fridge lives doesn't get as much ventilation as is needed...


I can install a couple of 12 VDC fans in the area to try to cool the area down...on in and one out maybe..


Thanks for the suggestions

One additional point on the Stainless Lobster, there is a fan associated with the SL that runs inside the box.

I use an RV fan inside the refer to circulate the air. It costs maybe about $15. Uses 1 or 2 D cell batteries. Certainly helps keep the refer temperature more even from top to bottom.

catalinajack said:

Yes, the Danfoss compressor has a provision to drive a fan of up to .05 amps. My two fridges are set up that way and they keep cold during the summer. But, what if one would want to use a fan that draws more current to get higher CFM? Could one use that circuit to drive a relay so that power to the fan is not taken from the compressor? My fridges are 12-volt only so I have ready access to independent 12VDC. Would a common automotive relay work?

Click to expand...

The controller can handle 0.5 A, [500 milliamps], far more than .05A [50 milliamps].

To drive a fan that draws more than 0.5 A you would use the controller output to operate a small 12V relay such as from Omron, or many others. THey typically draw 0.04A or 40 milliamps. Then the relay can handle much more current than the controller directly. Often up to 10A. However for loads like that I would install a diode on the control side of the relay to protect the controller.

The fan I used draws 50 mAmps so you could theoretically use 10 of them and draw .5 amps. So I don’t see any reason to complicate it with a relay. You shouldn’t need more than 2 fans and you will be well below the max available draw.

I was not suggesting he complicate things but he asked about a larger fan.
I think I assumed incorrectly much larger.
You are right though the output can handle, from NovaCool , up to 500 milliamps.
But I would not load the output fully either. I have seen fully loaded outputs die.

I can’t imagine that he would need more than 2 fans. I only use 1 and it made a huge difference. But maybe he has a really strange cabinet???

It was I who posed the question about using a relay to power a larger CFM fan. Given that it seemed that some folks do not have a well-ventilated enclosure I was thinking that this might be a solution for them, a larger fan, but not an annoying monster.

I removed the existing two-fridge enclosure from the DeFever 44 we purchased and built a new enclosure that provided a two-inch space under the floor. I drilled a series of two-inch holes in the floor toward the back for air flow plus the floor does not extend all the way to the back. The cabinet has grill vents on each side at the top back so air is drawn from the front underneath and is pushed out the top on both sides by the muffin fans powered by the Danfoss compressor.

The cabinet was constructed of 3/4 plywood with dados to fit it all together. The individual panels were brought aboard and screwed together, no glue. I then brad-nailed (air-powered) two-inch wide teak tongue-in-groove boards to finish the sides and front trim. The top is a custom-made teak countertop that is screwed into place from underneath (about $600). All-in the materials cost about $750.

The only mistake I made in building the cabinet is that I should have made it slightly larger to accommodate some additional insulation. Still, with the addition of the fans and good ventilation, even in the heat of the summer we have never had to set the thermostats at their highest. In fact, sometimes we freeze delicates like lettuce if we are not paying attention to the ambient temps.

The fridges are fridge only (no freezer section) Vitrifrigo 12VDC only units. We have a seven cubic foot chest freezer on the flybridge deck. We also have a Scotsman commercial icemaker on the aft deck, all the comforts of home for these live aboards.

Anyway, the relay idea was just something that might be an option for some folks, fan size to be determined by personal needs.

C lectric said:

I was not suggesting he complicate things but he asked about a larger fan.
I think I assumed incorrectly much larger.
You are right though the output can handle, from NovaCool , up to 500 milliamps.
But I would not load the output fully either. I have seen fully loaded outputs die.

Click to expand...

Well done. Looks like you have it covered.

I have a nova cool that is a fridge with a small freezer side by side. Can’t remember the model. I had trouble when it was new. Turned out it didn’t have the right charge of Freon. That fixed it. I also added ventilation before they came and recharged it on warranty. I bought a add on controller from coastal climate control that can vary the compressor speed automatically. You remove the resistor and plug the controller in it’s place. Check it out on their site.

As to lettuce freezing, we have had good results with the small RV inside the refer fan. They run off D cell batteries. It helps keep the air moving so the coldest air doesn’t stagnant on the bottom of the refer.

Comodave said:

As to lettuce freezing, we have had good results with the small RV inside the refer fan. They run off D cell batteries. It helps keep the air moving so the coldest air doesn’t stagnant on the bottom of the refer.

Click to expand...

I had two. They died after a few years. I forgot where I bought them.

We got our on Amazon, where else.

I have the NovaKool RFU9000, I use the MerlinII controller, it works as advertised. I'm sure it makes a difference in power consumption, although I don't have empirical data to back that up. I do know that in low load conditions (low ambient temps) it runs a lot on the lowest speed, and when it gets hot, it does kick up to high speed with greater frequency.



I also use a battery operated fan inside the box. It is effective at keeping the temperatures inside the box more even. I sit the fan on the top shelf in the back and its output blows up toward the evap coil. D-cells last a bit over a month.

I picked up a nice 12volt relay from Sure Maine Service in Seattle to power a water pump for my water cooled dan foss compressors. Works great. They even drew me a wiring diagram. Can’t say enough for their help over the years.

Sorry, that’s Sure Marine Service.

I have the Stainless Lobster in my NorKool 8000DC which includes a fan that runs with the compressor is running.
It replaced the original thermostat and bulb.