Norcold N842IM Replacement

Stan Birch said:

I added the insulation from the back, because there was a 1-2" air gap all around the top and sides of the fridge. I just tucked the insulation into the gap. Your fridge may not have been installed the same way.

I have never used a fan or anything other than convection air flow for cooling.

You might also check if it makes any difference when the outside fridge door is removed.

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When I was installing the Fan in the back I really did not notice any gap around the refrig sides. I did have the outside vent door off one afternoon and again didn't notice a real change.  I will take a close look tomorrow to see if there is any place I can add insulation.

Again, thank you.

-Russ

Stan Birch said:

I seem to recall that I had a MSW inverter that  used one additional stop before reaching peak.  ??

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Some of the MSW inverters have several steps while going back and forth across zero potential.

Modified sine wave is grossly inaccurate, they should be called modified square wave inverters.

There is seldom any "modified" about the square wave...

>>Modified sine wave is grossly inaccurate, they should be called modified square wave inverters.<<

Modified square wave or quasi square wave inverters is what I called them about 50 years ago when I designed a few.

Well, the modified square wave output does have a non-zero time at 0V whereas a true square wave goes directly from max minus to max plus and vice versa and is never at measurable true 0V at all.  I know, nit picking, but accurate

We are on a tangent here, interesting, but a tangent  .

Yes - I feel bad the thread took the direction it has.

If it will help, I will accept that the Dimension 2000 is a Square Wave Inverter and there is nothing 'Pure' about it. It is what came with my Journey and if I eventually go residential I will Not run the refrig on inverter power.

-Russ

Sorry for the digression. It was just a casual comment.

Gary RV Roamer said:

Sorry for the digression. It was just a casual comment.

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But hopefully educational.

Yes - Educational.

Thank you everyone for your input and sharing your knowledge.

As an update to my N842Im performance, thanks to the service manual link John gave me in one of the earlier posts, I was able to run the diagnostics and fold no 'error'. But can now see what the refrig fin temps are. After adding the back fan, it actually does appear to be helping when the afternoon heat starts to build here. I have learned that it seems these refrigs need almost 48 hours of run time from startup to sort of stabilize. I fired my refrig up about 40 hours ago and it is currently setting at -8 in the freezer and 33 in the refrig. I opened the door twice this morning to simulate use and the box temp went up to 38. That as around 9:00 am, and it is dropped back down to 33.6 at the time of this posting.

So again, thank you everyone for your input.

Russ

It sounds like you're good to go Russ!

RGrimm said:

I have learned that it seems these refrigs need almost 48 hours of run time from startup to sort of stabilize. I fired my refrig up about 40 hours ago and it is currently setting at -8 in the freezer and 33 in the refrig.

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The same applies when you dump a shopping cart full of room temp groceries into the fridge; it takes a good 12 - 24 hours to get everything back to status quo.

With a bit of testing, I've learned that it is really good idea to keep the fridge set at 9/max, even when the interior temps get down to 30 degrees on the thermometer. Worst case, you might mess up a head of lettuce, but that's rather unlikely, with best case avoiding sour milk and food poisoning.

After allowing good 12 - 24 hours for everything to stabilize, I scanned the food products with an infrared scanning thermo thingy. While frig temp was 30F, the milk on the shelf was still 45? !! While the milk-shelf on the door seemed to be the worst, checking item after item, showed significantly elevated temperatures compared to the interior frig temp. I suspect that it would take a number of days, if not a week to achieve homogeneity with the surrounding air.

As for risk of freezing, remember jr high school physics stuff:

It takes 1 calorie to reduce one cc of water 1 degree C.  While it might take 1 hour to drop the temp of a jug of milk 1? from 35? to 34?, changing the temp from  32? to 31?, which involves a change of state, that would take full 500 hours to drop the temp from 32? to 31? under the same conditions. Seems to be part of some sort of grand design, that without that single simple law of physics, the earth would be a mere lifeless barren wasteland.

Since I started this thread I thought I'd add and update to what I have found with the operation of my Norcold N842IM refrigerator.
The original post was looking to find if anyone had replaced my particular Norcold with a residential Refrig and was prompt by having cooling issues with the Refrig on a recent trip where we actually started to loose some food in the Refrig box. Let me also add that this is the first Norcold Refrig I have owned. My previous 2 RV's had Dometic Refrigs and were newer.
My initial assumption was that my Norcold was either failing or just not very efficient when the outside ambient goes up.  Since my last post in this thread, I have done more research and have run some tests on my Norcold and I thought I'd share my findings. One post on a Forum I read indicated that some of the Norcolds have a defrost cycle to help reduce the frost build on  the Refrig Fins (not the Freeze). The Defrost cycle occurs every 49 hours. Basically the Refrig shuts down for a period of time. I had read some posts on Forums that said the defrost cycle last 2 hours .... well mine lasted 4 hours. It is the defrost cycle that I think that got me in trouble on my last trip. Prior to our trip I powered up the refrig during the day a few days before we were leaving so it had a chance to get cold. Since I started the refrig during the day (around 11:00 AM or so) that meant that the defrost cycle was going to occur in two days and one hour (49 hours) later. That meant my Refrig was going to shut down for 4 hours during the hottest time of the day and when the Refrig would be used (door opened to get things). I am guessing that this was the problem on out trip.  The Refrig went into a defrost cycle during the heat of the day while we were opening the refrig door to get items. Four hours Off, in the heat of the day and then opening the refrig door created a situation that took the Refrig box temperature way above 40 degrees for hours. Absorption refrigerators just don't recover quickly.
I decided to run a 'controlled test' to verify that my Norcold actually went through a defrost cycle and what affects it had on the actual temperatures in the Freezer, Refrig Box and on the Refrig Fins. I added a digital Refrig thermometer with one sensor in the Freezer and one in the Refrig Box and then put the Norcold in it?s Diagnostic mode so I could display the Refrig cooling Fin temperature which the control board calculates from the resistance of the thermister  attached to the 10th Fin from the left.

During the test, the Freezer was basically empty except for some ice cubes in the ice maker bin. The Refrig box had about 24 bottles of water placed throughout the Refrig.  The bottles of water were put in the Refrig already cold. To read the Temperatures I had a Wireless Network Camera that would display all three temps (see photo below) so I could view and log the temperture changes from in the house. I had also added a external Fan just below  the roof vent to  help with air flow across the back of the refrig.

I started the Refrig on July 3rd around 4:50 PM.  I allowed it run over night without opening the door(s). In the morning on the 4th, I open the Refrig door to simulate getting coffee creamer out, closed the door and then a minute later open the door again to put the creamer back (bottle of water for this simulation).  The Refrigerator?s Temperature is set to number 8.  While the manual suggests a temperature setting of  # 4 or 5, I wanted to have the Refrig temp to be as close to 32 degrees as possible so that just normal use of opening the door would not push the box temp over 40 degrees. During the day as I walked by my Laptop, I would look at the temps and log them into a spreadsheet.  As the temps indicate after running through the night the Refrig seemed to reach it?s running  temps based on the #8 Refrig setting (Freezer -8, Refrig 33, Fin temp 18). On July 5th, at about the 49 hour from startuppoint, the Fin Temp started to go up which seem to indicate that the defrost cycle started.  The 3 Temps all began to climb for the next 4 hours with the Freezer seeing the biggest swing from -6  to 28 degrees, a rise of 34 degrees, but it did stay under freezing (32 f).  I never opened either door during the defrost cycle, but could see that doing so could have allowed both the freezer and Refrig temps to exceed safe levels.

So here are my concerns. A 4 hours in a defrost cycle seems excessive. I do not know if that time is hard set in the control board?s electronics or based on a Fin temperature.  Looking at the temperature rises I can see that if the defrost cycle occurs during the day, especially around a lunch or dinner time when the Refrig/freezer doors would be opened more frequently, that the refrig temps could easily pushed above the ?safe? zone. I suspect this is what happened during our last trip to Gaffney, SC. I was just unaware of the defrost cycle.  As I look at the data, it would make sense to start up the Refrig before a trip at 11:00 or 12:00 at night so that the defrost cycles would during the night when the outsides temps are cooler and the Refrig doors would probably not ne opened. But with a 49 Hour cycle (why 49???) the cycle times will creep and on a longer trip eventually start occurring during the morning/day. I read one post on a forum where the owner, aware of this 49 hour defrost cycle, would manually shut off the Refrig when the cycle started to force a reset of the 49 hour cycle.

Knowledge can be helpful. As I said, I thought my Norcold was failing, but after doing some research and running my own tests for data to better see what was going on with my Refrig, it appears that my Norcold actual works well once you understand how it is working and make some adjustments to how we use it.  On future trips, I will start (or restart) the Refrig late at night so that the built-in defrost cycle occurs during the night when outside temps are cooler and the Refrig doors would normally remain closed. Now that I know how to run the control boards diagnostics and can display the Refrig?s cooling Fin temps, it is easier to see what is going on.

While this posts is a bit off-topic from my original post for this thread, I think it may offer some information that may help others down the road who feel they maybe having Refrig issues on a Norcold. Having this information certainly would have helped me understand what was going on with my Refrig and what I could have done to prevent the problem and loss of food.

-Russ 

Date     Time      Frez  Ref Fins     Comment
July 3 4:40 PM 23 40 37 Re-Start after off 20 minutes
July 3 5:00 PM 22 42 34
July 3 5:16 PM 20 43 31
July 3 5:30 PM 18 43 29
July 3 10:00 PM -5 38 22
July 3 11:03 PM -6 38 21
July 4 8:00 AM -9 33 18
July 4 8:27 AM -7 33 20 After opening both doors to simulate getting something
July 4 8:50 AM -7 33 18
July 4 9:12 AM -8 33 18
July 4 12:10 PM -5 35 19
July 4 12:20 PM -5 33 19
July 4 1:20 PM -4 33 20 Open Door Simulation at 1:00 PM
July 4 2:15 PM -4 33 19
July 4 3:00 PM -3 33 19
July 4 11:45 PM -6 32 18
July 5 7:20 AM -6 31 18
July 5 8:50 AM -5 31 17 (9:00 am) Open Door Simulation
July 5 9:12 AM -5 32 20 12 minutes after Door Opened
July 5 2:00 PM -5 31 18 (Raining - cool out)
July 5 2:50 PM -6 32 19 (2:40 pm) Open Door Simulation
July 5 3:30 PM -6 31 17
July 5 4:45 PM -6 31 25 (Defrost Mode Starting) (4:30/4:45)
July 5 4:55 PM -5 32 24 (Defrost Mode)
July 5 5:50 PM -4 32 24 (Defrost Mode)
July 5 6:00 PM -3 32 27 (Defrost Mode)
July 5 6:20 PM -1 32 30 (Defrost Mode)
July 5 6:34 PM 1 33 32 (Defrost Mode)
July 5 6:40 PM 2 33 32 (Defrost Mode)
July 5 6:45 PM 3 33 32 (Defrost Mode)
July 5 7:00 PM 5 34 32 (Defrost Mode)
July 5 7:30 PM 10 34 32 (Defrost Mode)
July 5 7:45 PM 12 34 33 (Defrost Mode)
July 5 8:06 PM 16 35 33 (Defrost Mode)
July 5 8:36 PM 20 35 33 (Defrost Mode)
July 5 9:06 PM 24 36 35 (Defrost Mode)
July 5 9:35 PM 27 36 38 (Defrost Mode)
July 5 9:50 PM 28 38 37 (Defrost Mode)
July 5 10:00 PM 27 37 34 Coming out of Defrost
July 5 10:11 PM 26 37 31
July 5 10:24 PM 23 37 28
July 5 10:36 PM 21 36 26
July 5 11:00 PM 16 36 24
July 6 7:00 AM -8 32 17
July 6 9:20 AM -8 32 23
July 6 10:00 AM -6 32 19

Good data - thanks for posting it.

Thanks for doing the though study that recorded, very useful information.

Thanks Gary and John.

I am just happy that I don't have to deal with servicing or replacing this refrig in a coach I just purchased in April.  Now that I know what is going on, how the Norcold operates,  it is manageable.

I will run the refrig on #8 which sets the box temp to around 32/33 and I will run it in it's diagnostic mode so the Fin temp is always displaying. I know that during 'normal' operation the Fin temps are between 17 and 20.

Russ

Very methodical in gathering data.... but my test is putting a gallon of ice cream in, having it freeze rock hard so you can barely scoop it out & remaining that way over time.

In the olde country, Terry's ice cream test was how we 'calibrated' the fridge thermocouple, but used a slightly 'softer' criteria.

Outstanding data gathering Russ and thanks for documenting your test!  I'm a guy that likes hard data to base decisions on or for diagnostics.  At first blush, I don't like your freezer temperature approaching freezing but practically speaking, any mass of frozen stuff in the freezer probably won't warm up very much, like the "ice cream" test.