Fridge Performance Survey

[Raspy]

ZachO,

The fan circulates the air mechanically around the box, so it can efficiently get the cold from the upper plate to food down lower. Blowing air cools better than just convection.

Because it cools better, it is pulling more heat away from the plate and tending to make everything more even in temp.

But the result may look like the plate is too warm, when actually it is just giving up more heat to the box. But, of course, if it isn't producing enough cold, the whole box will be too warm and there will be no freezing. So it looks like it isn't working. It is, but with not enough capacity, in this example, to cool the box and freeze.

The fan, while helping to cool the interior, will also tend make everything the same temp. Result: You may have frozen food in the bottom, or you may not be able to get a freeze in the upper freezer compartment.

I put a fan in the system I had on my boat and left it on all the time. A very small one about 2" in diameter. All the food got down to freezing and I adjusted the thermostat to just barely not freeze the beer or the milk. But I couldn't have a separate freezer compartment.

RV fridges are at such a disadvantage with an extremely hot back side and a cold interior. Often with poor ventilation. Venting the heat is critical.

If yours works the same on 120 as it does on propane, you can probably eliminate the propane flame as the problem.

[redbarron55]

At some point you need another fridge.
If the 120 vac doesn't cool either it might be time.
I didn't have a decent fridge in my old Scamp when I bought it and I was going to use an ice chest since my previous three way fridges had not been satisfactory and I like to have some Ice handy anyway.
Instead I cane upon an older Norcold 704DE I took a chance on and it has serve well after some work, It is a swing compressor unit and I have now installed a 100 watt flexible solar panel on the roof with a charge controller and it seems to take care of the load when not connected to mains power.
If I turn it up too high it will put ice in the beer and freeze the diet cokes solid.
I occasionally see one of the small pop up fridges on Craigslist or ebay, but you might end up buying one that works like the one you already have,

[ZachO]

In the end I guess I don't believe that a dorm fridge will really work for me. Too much electrical demand for a guy who essentially never plugs in. But I don't want to go too far off topic.

I currently have my fridge plugged in, and it's supposed to get almost to 90 today so this'll be a good test.

I do still have some work to do. I kind of messed up and did things in the wrong order...there is about a 1 1/2-2" gap above my fridge. Anything over 1 1/2" is supposed to be filled, and the specs from Dometic are 0" for the space above.

I put a curved deflector over the fins, along the top of the upper vent. But didn't fill the space above the fridge. If the deflector created an actual seal, it would be fine, but there are some spaces for hot air to get through and collect in the upper compartment. So it may be a good idea to take the deflector back out, fill the air space back there above the fridge, then put the deflector back in.

If, with no space for hot air to stagnate, a fan running, and everything else I've done, I still can't get good cooling, then I guess I'll start saving for a new cooling unit.

I'm still worried about my off-center burner...that seems unsafe but I even emailed Dometic with that photo and haven't heard anything. I guess today would be the day to look at how to center it, since I'm running on AC.

[Joe & Cherie]

I know this doesn't help much but we used our 12v only Norcold 751 for 48 hours last weekend boon-docking. No solar. After that time running fridge, very little LED lights, and the MaxxFan on low for one night - we ended up the weekend at 12.15v left in our pair of Trojan T-105's. I forgot to check the V before we started the trip but they were plugged in for 2 days so probably fully charged around 12.65.

I really like the 12v only compressor fridge. I think it uses 3ish amps while running (50% of the time) and cools well below freezing on a hot day. I have no idea how much solar one would need to stay charged......

[ZachO]

With some of the quick searching I've done (so far I'm not seeing much useful info for my lifestyle with an electric-only fridge), it seems like I'd need the fridge (obviously), two batteries, and double the solar. Based on high-efficiency DC fridge costs, with a second battery, another 100W solar and whatever incidentals are involved in the installation and connection of all these parts...

I'd be looking at around $2,000 to make the switch.

Ideally, I'd be running a DC fridge and have a good battery bank and solar setup. In reality, if I can coax just 5-10 degrees more cooling out of my fridge in 80 degree + weather, I'm just going to have to be happy with what I've got. Even a new cooling unit on my fridge, assuming that would actually perform better than my current one, is less than half the price of switching to a DC only fridge.

So...I'll be sticking with what I've got and trying to squeeze a couple degrees more cooling out of it, I guess.

[Civilguy]

Originally Posted by ZachO

In the end I guess I don't believe that a dorm fridge will really work for me. Too much electrical demand for a guy who essentially never plugs in. But I don't want to go too far off topic.

I currently have my fridge plugged in, and it's supposed to get almost to 90 today so this'll be a good test.

I do still have some work to do. I kind of messed up and did things in the wrong order...there is about a 1 1/2-2" gap above my fridge. Anything over 1 1/2" is supposed to be filled, and the specs from Dometic are 0" for the space above.

I put a curved deflector over the fins, along the top of the upper vent. But didn't fill the space above the fridge. If the deflector created an actual seal, it would be fine, but there are some spaces for hot air to get through and collect in the upper compartment. So it may be a good idea to take the deflector back out, fill the air space back there above the fridge, then put the deflector back in.

If, with no space for hot air to stagnate, a fan running, and everything else I've done, I still can't get good cooling, then I guess I'll start saving for a new cooling unit.

I'm still worried about my off-center burner...that seems unsafe but I even emailed Dometic with that photo and haven't heard anything. I guess today would be the day to look at how to center it, since I'm running on AC.

Zach,

I'm going to continue risking being wrong here; I've got no pride.

I am "guessing" that the refrigerator is fundamentally working, meaning that you are boiling the ammonia sufficiently to create a proper refrigeration cycle, as evidenced by the cool-weather operation, but the whole system is being overwhelmed by "waste heat" which is not being adequately removed.

We just ran our refrigerator for a week in cool weather on the coast on AC power a week ago and it worked great as monitored by a pair of thermometers in the fridge. We ran it mainly from 2 to 3 on the five-step settings scale.

We had issues while operating on LP in hot weather last year. Our refrigerator compartment temperatures were marginal, though not nearly as bad as you have reported. We had shade on the street side from trees and our awning.

The horizontal fiberglass surface over the top of the refrigerator inside our Casita was very hot to the touch; much hotter than our ambient high-80's temperatures. It was basically excess heat from the propane burner which produces much more heat than the electric heating element used on AC power.

I think this episode underscored the importance of insulating and/or blocking the hot air from getting into the spaces where it will surround the refrigerator.

Recalling the installation diagrams, they indicate a need to limit clearance at the back to 25 mm (1"). I believe that this is done in order to force the naturally rising warm air circulation to move through the coils. On the Casita, the factory installation has up to 3.5" inches of clearance. I am going to try and arm-wrestle some sheet-metal baffling in there when I get my round-tuit (hopefully before our scheduled late-July trip to the east side here). I count that as item No.2 which needs to be improved on ours.

Some of the forum posts noted improvements when the upper vent grill was removed. I expect that would provide some minor improvement to the natural upward air circulation. I tried that last year but there was no way to measure the effect.

Since you have been working with sheet metal, can you cobble together a temporary exhaust chimney to remove the heat from the top of the boiler tube? If so, maybe you could run it out the side with the vent cover removed. As a temporary item, and something that's going to get pretty hot, I'd keep an eye on it and take care not to let it contact plastic and fiberglass.

I may be wrong, but I really think the issue here is one of removing the excessive heat at the top and also potentially of improving the circulation over the coils. And, yeah, addressing the off-center flame would probably be a good thing to do too.

You might also try sending a PM to Brian B-P. He's not active in posting on this forum anymore, but he's still active on the Escape forum and I know he's still lurking around reading posts here (Hi Brian!). He's good at separating fact from fiction and dealing with some of the more complex issues; maybe he can offer something that will help you out.

[Joe Romas]

After replacing my badly rusted refrigeration unit to avoid a possible failure I needed to totally redo all my refrigerator mods. There is as much fiberglass packed all around as possible.
The tube pointing rearward is to help eliminate the flame blowing out on the road but I also added a re igniter that instantly relights the furnace.
The aluminum in front of the fins also catches rain water and directs it outward.

Sitting in the driveway my current problem is keeping the refrigerator above freezing

Joe

[ZachO]

So you've got some dryer ducting coming off the top of the flue/chimney, vented to right under the curved sheet metal for easy venting? Is that what I see? I'll look at mine again tonight and see if I can do the same.

I will see how I'm cooling on AC when I get back home in a little bit. It's about 90 today so it should be a good test.

Having the shade on the fridge vent side obviously helps, but hasn't solved my issue so far. And yeah, seeing that glowing red chimney bottom scares me. I don't want to be one of the statistics/examples people cite when they're warning about the dangers of LP refrigerators.

I will try packing the upper gap with insulation, and venting the flue. We'll see where I have to go from there.

I may just break down and rent a room in a house for the month of July. That will give me more freedom to work on the camper instead of having to try to fit quick fixes in while I'm also trying to use everything.

[ZachO]

Well, on AC, with the temps just below 80 most of the day and currently at 83, my fridge is at about 43 degrees. Not too bad. Of course I only opened it once or twice, and most of my food is in a house so it's fairly empty in there, but I do think it's cooling better on AC.

So too much heat in the upper compartment could definitely be the issue. I still don't think it's going to do well in the upper 80s and definitely not well at all in the 90s, but if I can limp it along in the upper 70s to the mid 80s, I can be happy.

I'll work on the stuff we've been talking about and let you know how it goes.

[redbarron55]

Originally Posted by Joe Romas

After replacing my badly rusted refrigeration unit to avoid a possible failure I needed to totally redo all my refrigerator mods. There is as much fiberglass packed all around as possible.
The tube pointing rearward is to help eliminate the flame blowing out on the road but I also added a re igniter that instantly relights the furnace.
The aluminum in front of the fins also catches rain water and directs it outward.

Sitting in the driveway my current problem is keeping the refrigerator above freezing

Joe

The metal baffle that comes to the bottom of the top fins should seal up the rest to that side as well.

All of the draft should go between the fins and not be able to go around it on either side.
Just my opinion.
Air that passes by the cooling fins with out going between fins is wasted.
The top side of the fins need to be exhausted out the side (or top)

[redbarron55]

Not the same thing, but on my Norcold 704DE I added more surface area to the cooling fins to transfer the heat out and up behind the fridge.
I used soft aluminum tape with Polyacrylic adhesive and pressed it over and around the small steel "fins" between the coils
You have to look carefully to see the added "Fins".
After putting them in paint them black to improve radiation and well as convection transfer.

The point is you could use the same aluminum tale to seal the side of that top coil as well.

[ZachO]

I'm not sure I have any idea what's going on there, but I'll see if I can get it...

Here are some photos. You can enlarge them if you're logged in.

The vent


The baffle looking down from the top vent


Baffle looking up from bottom vent


The curved metal deflector above the fins


The reason I'm not sure how to vent the top of the chimney/flue. Should I just remove this piece so I can fit a vent tube over the top? This is looking down at the top of the chimney


The reason the off-center flame worries me. It's actually burning away part of the chimney bottom edge

[redbarron55]

I think I would look at centering the burner if you can.
I would also seal the gap between the baffle and the square fins to keep the air from going around rather than through.
What are all of the tubes(?) that seem to be taking up a great deal of the space for the exhaust of the hot air?
It looks like they are taking up more than 2/3 rds of the venting area.
If you can move them against the back of the vent to give a clear path for the air leaving.
It also looks like there is excessive clearance on the back of the unit and you might check that out against the specifications
This could be a good part of your problems along with the non centered burner.
Here is a write up on clearances for a Norcold, but yours should be similar.
Added video that mentions centering burner:

https://www.youtube.com/watch?v=FCqiVqZx5k4

https://www.youtube.com/watch?v=6jlbpB0lwkc

http://bryantrv.com/reefer.html

[ZachO]

Those tubes are water, to and from the water heater. I'll see if I can tuck them back a little, but I honestly don't think they're going to move more than an inch any direction.

And that flue cap/heat deflector he talks about in the second video is exactly why I can't figure out how I'd get a tube vent on the flue to direct the air away. Unless the deflector is just meant to...well I guess do exactly what its name says and deflect heat away from the back of the fridge. In that case, anything, including a chimney extension/tube, that directs the heat away, would work. I just don't want to remove something that needs to be there.

I definitely don't have rust in my burner, and last time I had the fridge out, earlier this spring, I ran a shotgun cleaner through the chimney.

Are you saying to extend the baffle so that it's actually contacting the fins?

[redbarron55]

Yes the tolerance is on one of the pictures zero is the minimum.
The units were made to be close to touching the back wall.
Does your unit have the turbulator in the pipe?
The video shows the bottom hot and cooler at the top.
Is it?

[ZachO]

Ok.

Yes, it's there. I just looked at it to make sure the cap/deflector was angled right, though nothing in the manual says which way is "right". Mine is different than the one in the video. But yes, the "flue baffle" is there.

I don't know if there's a heat difference, but next time I take the vent cover off I'll check. Would this be on electric and gas operation, or only on gas? And does this guy know that it's supposed to be that way or is he just guessing?

Anyway, we'll see. It interesting to see how much difference the vent cover makes. I had it off for a while, and the exhaust fan had shut off. I started putting it back on, and wasn't even finished putting the screws back in before the fan kicked back on. Getting that hot air moving out of there certainly won't hurt...

I saw a thread a few days ago where someone mentioned a newer vent cover design Dometic came out with. Better venting, but let a bit more water in with heavy downpours. But the nice thing was that both the upper and lower covers opened. So I wouldn't have to unscrew the top cover every time and deal with more and more of the screws stripping, or with butyl tape.

[ZachO]

After taking off the vent again today, I realized I was wrong about the air gaps. There is zero space between the top of the fridge and the cabinet. But there's about an inch of space on one side of the fridge, probably 2 inches on the other side.

I'm not pulling the fridge again any time soon, so does anyone have advice on what to insulate the sides with? It's going to need to be something I can kind of stuff in there, working between the upper and lower vents, basically getting it "good enough" to more or less close off that airspace. I'm guessing it needs to be non-combustible.

Looked at dryer venting tubes today but I don't think they'll work for venting my chimney with the way it's set up.

I closed some of the gaps around my upper air deflector with metal tape. Doesn't seem like it sticks very well so I don't know that it'll last long...but we'll see.

Fridge has been cooling great on AC but it hasn't gotten hotter than 70 in the last couple days.

[Joe Romas]

If your referring to my flexible aluminum tube it's NOT a dryer vent.
It's 1 3/4" aluminum from NAPA autoparts.

Here's a Dometic chimney extension that's not available in the US. that's where ny tube solution came from.

http://www.everythingcaravans.com.au...aravan-fridge/

Also from your bottom looking up picture it looks like there's no bottom vent.

Dometic specifies a deflector be below the bottom tubes with a space no more than an inch. On mine I mounted it to the 3 screw tabs on the bottom vent frame.

[Civilguy]

Originally Posted by ZachO

I'm not pulling the fridge again any time soon, so does anyone have advice on what to insulate the sides with? It's going to need to be something I can kind of stuff in there, working between the upper and lower vents, basically getting it "good enough" to more or less close off that airspace. I'm guessing it needs to be non-combustible.

I have always thought that packing some fiberglass batt insulation (without the backing paper) into the gaps would serve fine. I seem to remember reading some posts on along that line.

However, I just saw something on FitRV yesterday. The Class B manufacturer used a tenacious caulking-type sealant when they installed the refrigerator because they were trying to ensure that no carbon monoxide would enter the occupied space. The fellow removing the refrigerator was commenting on how difficult it was to remove; he used an oscillating multi-tool with a putty blade.

"Removing everything from the cabinet was tougher than I had expected. Most RV construction is screws or “stick and staple”, but when dealing with an absorption fridge, there’s a “chimney” in the back of it that has to be sealed off, airtight, from the living space. This is necessary to keep carbon monoxide, engine exhaust, and who-knows-what-could-happen-if your-“ammonia-boiler”-breaks fumes out of the living area. So there was a rather large passageway behind the fridge that was glued together with copious amounts of very tough, impermeable sealant."

https://www.thefitrv.com/rv-tips/rep...-2-demolition/

So, maybe sealing against gasses is a good thing to consider...

[Civilguy]

Originally Posted by Joe Romas

It's 1 3/4" aluminum from NAPA autoparts.

Joe,

I saw this back when you posted the pictures and I really like it.

I had bookmarked the source for the Dometic Australian part long ago but I have never taken action as 1) was going to try other fixes including fans and baffles first, 2) I didn't want to commit to installing the chimney vent plate through the plastic vent panel, and 3) my "cheap" gene often kicks in and overrides any precipitous actions like clicking on "buy" buttons.

How often have we bought some very cool thing and then realized it could have been done for 10% of the cost?

I expect I may take the Napa route and give it a shot, perhaps strategically aligning a fan to dissipate the heat emerging from the top. Thanks for posting. I continue to learn...