A few more tests of new Isotherm frig

[booster]

Our first time in hot weather trip this spring showed that the new frig did not perform as well in hot weather as the 10 year old same model that had died. Temps got as high a upper 80s so not extreme at all, though.


It seemed to be running out of cooling capacity to the frig section and running a very high percent of the the time. Slow to recover when food added, bottom of frig temps rising with freezer temps dropping.


The biggest differences between the old and new frig were a shroud around the freezer (evaporator) box, and much tighter fitting freezer door, and a different design drip tray. From the time it showed up I wondered how it could get enough cold air out of the freezer box to cool the frig area well as it was nearly completely blocking airflow on the outside and letting no cold air drop past the door. It did pass my early tests on the bench, though, in low to mid 70s temps and no contents except a gallon of water for thermal mass.


When we got home from the trip, with the drip pan removed to help it out a bit for the last half of the trip, I looked closer and could see the frost had very quickly built up under the shroud, completely blocking the air from getting through the vent slots in the shroud. That might explain why the cooling got progressively worse during the trip.


I removed the shroud from freezer box and made a quick way to hold the freezer door open to various gaps. With it out in the sun on a 90* day it ran well and very similar to the old frig. I found having the freezer door open 3/4" worked well.


As long as I was testing I decided to try to quantify the issue of food blocking internal airflow that we have always had with the small frigs. I put a couple bath towels on the shelves to block all the air movement through the shelf area, and then took temp readings in the freezer, upper shelf, lower shelf, and frig bottom.


With the shelves blocked I got the following results.


Freezer 20*, top shelf 31.5*, mid shelf 38.5*, bottom 41*


This is similar bottom temp we commonly see on trips with a packed frig. We haven't monitored top shelf temps much, though. I don't like those temps with freezing at the top and borderline cold enough on the bottom.



I ordered some of this corrugated material to see if putting some top to bottom airflow could be created.


https://www.homedepot.com/p/Falken-D...2460/316676642


I was surprised to see very little improvement


Freezer 20*, top 31*, mid 37*, bottom 39.5*


I then pulled the towels back a ways in the corners, probably a 2X2" triangular shape in each corner, and things got quite good.


Freezer 20.5*, top 33.5*, mid 36.*, bottom 37.5*


Assuming the open area to be defining issue, I removed the corrugated plastic side venting and put some PVC pipe pieces in the corners of the rear of the frig where the towel openings were. They are need to prevent food from blocking the shelves. The improvements seen in the last test got badly reduced.


Freezer 20*, top 31.5*, mid 37*, bottom 39*


Now assuming that the tubes was picking up air higher off the top shelf prevented from getting good airflow from the lowest point where it is colder, I ordered a couple tiny 20mm computer fans. They move small amounts of air and only use .035 amps of current apiece.


The fans did not make a significant difference. I tried both blowing down, both up, one each way with minimal effect. I was very surprised to say the least.


This meant stepping back the original plan of having the corrugated plastic in place, as it was there on the towel moved away from the corners test that gave the best results. I left the pipes in place and tested with the fans on and off. With both fans blowing down, I got the best results of the testing.


Freezer 20*, top 33.2*, middle 35.2*, bottom 37.2*



This matched the 4* difference top to bottom of the open corners test with corrugated plastic. Unfortunately, the simple thing of leaving the corners open doesn't seem to have a practical way to be done in the real world of food loading, so for now at least we will stick with what we have with the fans and pipes, plus the corrugated plastic. These temps and air movement will give us some better range for when the temps swing a lot at night to the cold side, I hope, as the frig does run colder with lower outdoor ambients as it vents outside. We should know more about that after our fall trip that will likely see some lower temps, possibly into the 30s*.


Here is what the corrugated plastic looks like in place. It is hard to get air by the shelves so have to have pieces above and below the shelves except in the rear where the shelves can be pulled out enough to use continuous.






This is what the PVC pipes and fans look like in place. The blue switch turns the fans on and off but also goes off with frig on and off switch I added early on.








Testing setup with towels blocking airflow to simulate packed in food.





I would encourage others to try the airflow blocking test to see how their frigs behave under that worst case scenario, as it is truly interesting, I think. I have always wondered how the tall and skinny units like the one davydd has on his new van do for the temperature difference top to bottom range.

[@Michael]

Interesting.

Using towels look like a good way to simulate a full fridge. Good idea.

Presumably the fans force a circulation more reliably than convection alone.

I suspect that different fridges will behave differently, so one would have to do one's own tests.

[booster]

Originally Posted by @Michael

Interesting.

Using towels look like a good way to simulate a full fridge. Good idea.

Presumably the fans force a circulation more reliably than convection alone.

I suspect that different fridges will behave differently, so one would have to do one's own tests.

I would expect different frig designs to be quite different, mainly depending on where the freezer is located and how the air can get back up to it to be cooled.


I though on ours the air would drop down along the door and them come up through corrugated plastic but that didn't really happen much until I added the fans and tubes to force the air down, or if I left larger gravity opening in the corners.


The outside walls of the frig are going to be the warmest areas inside the frig, so the air in corrugated should rise and carry that heat up to the freezer area to get cooled, but the door must do the same thing and essentially block the cold air with it's rising warm air. The fans seem to be able to get that air moving better to overpower that issue, even as small as the fans are.

[avanti]

I am hoping my forthcoming dual-compressor Isotherm will obviate all of that. I will know soon. Stay tuned!

[GeorgeRa]

Interesting experiments. I didn’t test mine in elevated temperatures but had no issues at 80F. My key questions are related to:

1. Sensor location: on the cold plate it controls the freezer temperature not the fridge, fridge control is open loop relaying on heat transfer from the freezer to the fridge. Electronic sensor located in the fridge controls fridge temperature.

2. Heat transfer restriction between the freezer to the fridge, which you are attempting to modify with a corrugated plastic, it is a key factor to keep uniform fridge temperature. We rarely fully pack our fridge co cold air has sufficient routes to move downwards.

I wonder if adding an aluminum heatsink to the bottom of the fridge could help in heat transfer. Ice buildup could be a problem, perhaps fins spacing could prevent it. Good luck.

[booster]

Originally Posted by GeorgeRa

Interesting experiments. I didn’t test mine in elevated temperatures but had no issues at 80F. My key questions are related to:

1. Sensor location: on the cold plate it controls the freezer temperature not the fridge, fridge control is open loop relaying on heat transfer from the freezer to the fridge. Electronic sensor located in the fridge controls fridge temperature.

2. Heat transfer restriction between the freezer to the fridge, which you are attempting to modify with a corrugated plastic, it is a key factor to keep uniform fridge temperature. We rarely fully pack our fridge co cold air has sufficient routes to move downwards.

I wonder if adding an aluminum heatsink to the bottom of the fridge could help in heat transfer. Ice buildup could be a problem, perhaps fins spacing could prevent it. Good luck.

Re 1 Yep, that is why my tests so very close freezer temps as I did not change the thermostat setting. The results would indicate I could take it a bit warmer on the thermostat and still have the bottom be safe. That would raise the freezer and top shelf temps somewhat and that would help efficiency.


Re 2 Getting the shroud off seems to mostly have taken care of the heat transfer rate from evaporator to the frig air, but basically doubling the heat transfer area by using both the inside and outside of the evaporator which is also the box sides, top, and bottom by leaving the freezer door open also really helps as the comes out colder and heavier.


R 3 Don't know if a finned heat transfer sink would help or not. I did try blowing air at the freezer box and it did little to change any of my reading which was a big surprise.


On edit- Thinking more about more heat transfer into the evaporator/freezer skin might actually be bad thing, if you can't get that colder air off the top shelf to the lower shelves and door. The top shelf would just keep getting colder and it is already the coldest place in the frig section of the unit.


I wish we could somehow not overpack the frig, but a lot of the stuff we like needs refrigeration.

[Philip53]

For my new van, I ordered what I thought was the best marine combo fridge freezer I could find. Our first trip showed that the Isotherm was a disappointment. The freezer did great, but he fridge had issues with erratic temps. After a few days, I found the upper mounted fan was not running.

After returning home & calling Isotherm, they sent me a new fan. When installing the fan I found that the factory had wired the original fan incorrectly, and while it worked (probably in reverse) for a short time, it crapped out very soon on our first trip out.

I thought I had the fridge issue sorted out with the new, correctly wired fan, but, on our next trip, it still had issues keeping the fridge at even temps. Very frustrating. I called Isotherm again & they sent me a new controller, and another fan. Before I pulled out the unit to install the controller, I did some testing. Even though the fan was blowing a bit of air, it did not seem like much at all. By holding a piece of tissue paper by one end and placing it in front of the fan, it barely moved and actually sucked in around the edges. I looked at the design a bit closer and noticed the fan, when installed in the recess, was extremely close to the back wall - really close. I thought this may cause the fan to cavitate, or recirculate the air since it did not have a good enough area for clean air entry. Anyway, I was able to simply mount the back of the fan onto the mounting fan outside holes, giving plenty of room for the air to flow into the rear of the fan. This made an immediate difference when checking with the tissue - it straightened out like a flag in a stiff breeze! Closed it all back up and it has worked great ever since, keeping extremely close and even temps throughout the fridge.

The picture shows the fan mounted outside of the recess where it was originally installed. I have the grill laying on the shelf in front of the fan.

[avanti]

Well, that is disappointing. The Cruise 195 is one of the things I have been looking forward to. Thanks for the detailed documentation. I will be prepared if this proves to not have been an isolated issue.

[booster]

Originally Posted by Philip53

For my new van, I ordered what I thought was the best marine combo fridge freezer I could find. Our first trip showed that the Isotherm was a disappointment. The freezer did great, but he fridge had issues with erratic temps. After a few days, I found the upper mounted fan was not running.

After returning home & calling Isotherm, they sent me a new fan. When installing the fan I found that the factory had wired the original fan incorrectly, and while it worked (probably in reverse) for a short time, it crapped out very soon on our first trip out.

I thought I had the fridge issue sorted out with the new, correctly wired fan, but, on our next trip, it still had issues keeping the fridge at even temps. Very frustrating. I called Isotherm again & they sent me a new controller, and another fan. Before I pulled out the unit to install the controller, I did some testing. Even though the fan was blowing a bit of air, it did not seem like much at all. By holding a piece of tissue paper by one end and placing it in front of the fan, it barely moved and actually sucked in around the edges. I looked at the design a bit closer and noticed the fan, when installed in the recess, was extremely close to the back wall - really close. I thought this may cause the fan to cavitate, or recirculate the air since it did not have a good enough area for clean air entry. Anyway, I was able to simply mount the back of the fan onto the mounting fan outside holes, giving plenty of room for the air to flow into the rear of the fan. This made an immediate difference when checking with the tissue - it straightened out like a flag in a stiff breeze! Closed it all back up and it has worked great ever since, keeping extremely close and even temps throughout the fridge.

The picture shows the fan mounted outside of the recess where it was originally installed. I have the grill laying on the shelf in front of the fan.

Is the evaporator behind the panel that the fan is on so it pulls air though it? It looks like it might be that way.



It doesn't appear you need lots of air to do most this kind of stuff, or home frig has fan but you can't feel any real breeze at all and it works fine, for instance.


It seems that most fan installs I have seen concentrate on random multidirectional or horizontal like the one in the pic. I found only vertical movement to help our frig. The only other setup I recall that did that was the 3 little fans on the evaporator of absorption frigs we have seen and somebody actually sold as a kit.

[Philip53]

The air is pulled up through a sort of duct & blown out across the shelf towards the door, & 'falls' down to the bottom of the fridge, where the cold plate is, to repeat the circulation.

Like I said above, it works great now that I moved the fan out an inch or so. Sometimes the sales/marketing people override the engineers. I guess they wanted that back dimension to be as far back as possible for a greater capacity label. I can't be the only person to have had this issue, although I guess most folks would simply keep turning down the fridge control until everything stays cold, or freezes. I did install their optional digital temp display & controller for optimal compressor efficiency. Knowing then what I know now, I would still buy the Isotherm Cruise, but not the optional control/digital display.

And I am careful not to place anything bulky directly in front of that fan, but of course, that is good advice in any fridge.

[booster]

Originally Posted by Philip53

The air is pulled up through a sort of duct & blown out across the shelf towards the door, & 'falls' down to the bottom of the fridge, where the cold plate is, to repeat the circulation.

Like I said above, it works great now that I moved the fan out an inch or so. Sometimes the sales/marketing people override the engineers. I guess they wanted that back dimension to be as far back as possible for a greater capacity label. I can't be the only person to have had this issue, although I guess most folks would simply keep turning down the fridge control until everything stays cold, or freezes. I did install their optional digital temp display & controller for optimal compressor efficiency. Knowing then what I know now, I would still buy the Isotherm Cruise, but not the optional control/digital display.

And I am careful not to place anything bulky directly in front of that fan, but of course, that is good advice in any fridge.

So they are pulling the cold air up to the top after picking up the warmer air that gets trapped at the bottom? Interesting idea if that is how works.


I assume you got the ICT automatic unit? If so, you probably ran into the same issues that I did. Discussion is here https://www.classbforum.com/forums/f...lts-12476.html

[Philip53]

I believe they call it the ITC (interior temp control?). I do remember reading that post of yours a while back, when I was having these issues. You went into a great detail on your testing! Like I said, I would not advise anyone purchase that option.

Definitely the cold plate (evap plate), is located on the bottom of the fridge, maybe the bottom rear, I don't remember exactly. The fan pulls up the cold air & blows it out across the top towards the door, and as cold air falls, it descends to the cold plate to be chilled further & then sucked back up again. I would not say it is picking up trapped warm air, that is simply the circulation flow through the interior.

[GeorgeRa]

Originally Posted by Philip53

I believe they call it the ITC (interior temp control?). I do remember reading that post of yours a while back, when I was having these issues. You went into a great detail on your testing! Like I said, I would not advise anyone purchase that option.

Definitely the cold plate (evap plate), is located on the bottom of the fridge, maybe the bottom rear, I don't remember exactly. The fan pulls up the cold air & blows it out across the top towards the door, and as cold air falls, it descends to the cold plate to be chilled further & then sucked back up again. I would not say it is picking up trapped warm air, that is simply the circulation flow through the interior.

How variable the temperature was?

By your rearrangement of the fan location and flow direction are you enhancing natural convection flow or inhibiting it. I think air flows down between the cold plate and the fridge inner wall and enters through the bottom slots, see the picture?

ITC - Intelligent Temperature Controller, where did you place the sensor?

[booster]

Originally Posted by GeorgeRa

How variable the temperature was?

By your rearrangement of the fan location and flow direction are you enhancing natural convection flow or inhibiting it. I think air flows down between the cold plate and the fridge inner wall and enters through the bottom slots, see the picture?

ITC - Intelligent Temperature Controller, where did you place the sensor?

The ITC/ICT thing is a common on for me beyond being a typo. We had a supplier called ICT the last place I worked


Anyway, the air dropping through the evaporator area would the natural circulation direction with no fan, I think, because of the warmth of the walls and door causing air to rise and the cold plate causing cold air to fall, as George said and I was heading towards earlier. The pic George found is very good and useful.


One of the general rules I have always heard in airflow and cooling is that you should always try to enhance the flow in it's natural direction and not fight it, so I think it is very possible the fan was not installed backwards at least in Isotherm's opinion but was intended to push the air down. The fan itself should be a bit more efficient that way also because fans normally push air through a resistance better than pull it through the same resistance and that is why you see two pressure ratings in complete fan design specs, a discharge max pressure and max suction negative pressure.


The setup they have there is very close to what I thought would work the best if it were blowing down over the condenser except I have to get the air to pick up the heat before the fan which is a harder to do and less controlled. As mentioned, I tried having the fans blow up and also toward the front and got considerably higher bottom shelf temp.


I think it would be very interesting to see blocked shelf temps as that seems to magnify the natural variations in temps that would be there in lesser degrees in normal use with stuff in the frig. Doing tests with the fan setup to blow out in on test and in on the other might give very interesting results that might help determine just how all this stuff really works in the real world.


I do like the way it is designed in general though. It is very close to how I thought it should be done, but is much hard to do in a frig with the evaporator built into the freezer skin.


On edit- Here is a link to a unit that is built to be used on absorption frigs that I mentioned earlier. In the questions section the mfg explains that is made to blow down.


https://www.amazon.com/Triple-Deluxe.../dp/B072BPYXS8

[Philip53]

Hey George, are the red arrows from the manufacturer, or were they added? At first glance it appears they are not original to the drawing.

When I first called the tech line at Isotherm, and told them of the problem, he did not dispute my findings that the fan was indeed wired incorrectly.

Could I be wrong, and he misunderstood, or did not know himself - of course. As this is not an absorbtion fridge, it may not work off of convection to the degree that an absorbtion one does. The temp probe that came with the ITC kit was installed where the directions stated, in the sidewall on the left side, looking in. In my intial troubleshooting, I used an instant read temp 'gun' to check the temperatures all over the inside of the fridge. The temps varied widely. And after my fan relocation I got very consistent temps at every spot within a couple of degrees, even in the door storage areas.

It also seems that every compressor home fridge I have ever had has their fan blowing out through the vents at the top of the fridge, but I must admit I never spent much time researching or troubleshooting fridges.

Anyway, my Isotherm works great now, and I can't see any way I could improve upon it's performance. Good airflow movement is essential in proper and even cooling of the interior, and I seem to have that now. Please continue to investigate and post your results here. This is interesting!

[booster]

Our home frig also blows out of the top, but that is where the evaporator is so they have to, or waste space with a lot ducting. I think on a bottom freezer it would blow up from the bottom if that is where the evaporator is unless they have two evaporators..



Home frigs also very heavily count on non blockage of the gravity airflow by the shelves and food. The used to have wire shelves like our RV frigs to let the airflow through and they had a lot trouble with temp variations when the started going to glass shelves that blocked the air movement. Now the glass shelf units seem to be using split shelves at different levels to allow air movement down the middle of the frig at least on the ones I have seen.



Of note is that our frig works fine without the fans or tubes if there is not a bunch of blocking of airflow so all the checking of temps I did under those conditions was really not valid for how we actually use the frig in real life.


One thing you may want to consider is putting some sort of guard on the lower vent holes to prevent food from sitting tight against it. Food in the frig seems to slide around a lot (or I turn to fast and too sharply) and even when left good room at any given point for airflow it wouldn't necessarily stay that way while driving. Bags of premade salads and bags of cheese are our worst offenders.

[Philip53]

I have also found that judicial positioning of food packages, containers, etc. is very important, and like you said, they tend to move around a lot.

[GeorgeRa]

Originally Posted by Philip53

Hey George, are the red arrows from the manufacturer, or were they added? At first glance it appears they are not original to the drawing.

When I first called the tech line at Isotherm, and told them of the problem, he did not dispute my findings that the fan was indeed wired incorrectly.

Could I be wrong, and he misunderstood, or did not know himself - of course. As this is not an absorbtion fridge, it may not work off of convection to the degree that an absorbtion one does. The temp probe that came with the ITC kit was installed where the directions stated, in the sidewall on the left side, looking in. In my intial troubleshooting, I used an instant read temp 'gun' to check the temperatures all over the inside of the fridge. The temps varied widely. And after my fan relocation I got very consistent temps at every spot within a couple of degrees, even in the door storage areas.

It also seems that every compressor home fridge I have ever had has their fan blowing out through the vents at the top of the fridge, but I must admit I never spent much time researching or troubleshooting fridges.

Anyway, my Isotherm works great now, and I can't see any way I could improve upon it's performance. Good airflow movement is essential in proper and even cooling of the interior, and I seem to have that now. Please continue to investigate and post your results here. This is interesting!

No need for further troubleshooting if your fridge works great. Air flow arrows I added to show my point.

Regarding US Isotherm support folks based on my experience I found their “know how” a little questionable, more of marketing then engineering expertise. I truly have difficulties to think that Italian engineers placed fan in wrong place with reversed air flow.

“As this is not an absorbtion fridge, it may not work off of convection to the degree that an absorbtion one does.”
Sorry, I don’t understand this point. Compressor or absorption fridges work similarly inside, cold is cold.

[Philip53]

Originally Posted by GeorgeRa

No need for further troubleshooting if your fridge works great. Air flow arrows I added to show my point.

Regarding US Isotherm support folks based on my experience I found their “know how” a little questionable, more of marketing then engineering expertise. I truly have difficulties to think that Italian engineers placed fan in wrong place with reversed air flow.

“As this is not an absorbtion fridge, it may not work off of convection to the degree that an absorbtion one does.”
Sorry, I don’t understand this point. Compressor or absorption fridges work similarly inside, cold is cold.

Thanks George, and you may be completely right, maybe I have it all wrong. I did not mention the fact that even though the fan quit on my first trip, that since I had ordered and received the Isotherm early in my build, I put in service and used it to hold drinks and ice cream bars (yum), while I worked on the van. I was really proud of the unit, with it's sleek appearance and dual compressors, but I did question once or twice it's cooling performance - the drinks were not always as cold as I thought they should be. This was before I installed the ITC. But I did not think any more about it until our first trip when it did not do the job. And that's when I found the fan not operating.

As far as the Italian engineers, I don't really know. But, for damn sure, if I did change their 'design', it would not be the first time I have improved a product for my intended use.

My statement on the absorbtion fridges was to booster's link to a site that discussed absorbtion fridges. I don't doubt their design would be a bit different in some respects from a compressor unit. I am not completely sure, but I don't remember any fans inside either of my previous RV absorbtion units.

[Davydd]

We have this Isotherm Cruise 115 (115 liter) which I selected mainly for size and efficient combination freezer that is reputed to hold 4 frozen pizza boxes or more importantly a half gallon of ice cream. I mostly stock can beer so the air flow with round cans is no problem. Most vegetables go into the ample bin at the bottom. We don't need to stock a refrigerator like we do at home and this was a compromise considering most under counter Class B refrigerators are smaller usually at 85 liter. I have had two absorption refrigerators and now two compressor refrigerators. I would never go back to absorption refrigerators.

The open storage space below the refrigerator was more important to me as it holds a cat litter tray out of the way when we bring our cat along or just more storage otherwise. It also brings the refrigerator up at acceptable height 17" off the floor and vent space up for the refrigerator and vent space horizontal for the under the bed lithium batteries.

Since I uniquely selected it, I had no other Advanced RV to rely on with experience. I just had faith that it was better than my previous Novakool 6800 two door refrigerator/freezer which I did have a problem keeping it cool enough. So now on the road I will have to experiment and test other than that thermometer attached to that wire shelf. So far I have detected no problems.