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Old 06-29-2022, 12:30 PM   #1
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what temps should I expect out of my Dometic RM3762LBX in hot weather?

Right now it's 92 degrees outside my 2013 26' Flying Cloud, I have the temp button set to 5 and we're at 35 degrees in there according to the faceplate thermometer. Just fine! However, last week when we were at 102 outside here in Austin, TX I couldn't get it below 50 consistently. The freezer worked fine, but the fridge just wouldn't stay cold. Is there some kind of "bad news" point in the mid-90s after which you just can't cool consistently? Will it improve if I put an exhaust fan at the top vent door?

Thanks!
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Old 06-29-2022, 01:14 PM   #2
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For the most part, Airstream violates the installation minimums because clearly there is limited room for proper ventilation. That is why you see most coming out with fans to pull the hot air out via a vent or exhaust grate.

I replaced my stock fan with two high CFM quite fans and even when the temperature hit 100 degrees with 85% humidity last year, our fridge remained at 37 degrees (our default value based on the settings).

You need to find a way to get the hot air out of the cabin space behind the fridge and force out the hot air to allow proper cooling of the fridge heat fins. I bet they were hot as hell to the touch under your conditions.
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Old 06-29-2022, 01:42 PM   #3
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I also replaced the fan in our 25', but to make it quieter. If you have side panels for the refrigerator (not a roof vent), prop them open and it will increase the effectiveness of the fan. We have been in 112 degrees and the refer was ok. Opening it as little as possible retains the cold.
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Old 06-29-2022, 01:58 PM   #4
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We had 90 degrees and it hit 42 in the refrigerator. But by morning it went down to 33. 50 seems pretty warm. The sun was beating down on that side when it hit 42. I have a small fan inside that circulates the air which helps. They do make better ones that go over the fins. Also I noticed our closet by the refrigerator was pretty warm. I didn’t do it, but I considered leaving it open and letting the AC air get into it.

But what kittmaster did may be your best bet. It is getting it wired that may be a problem. But an interior fan and figuring out a way to get the sides of the fridge some air may be your best short term bet.

A more expensive solution is put an awning on the fridge side (if it isn’t). I’ve thought about doing that just so that we wouldn’t have to run AC so much and allow for more fresh air when sunny. Also would give us another place to sit.

It seems that the absorption fridges have these kinds of issues. I have heard of people putting ice chunks in the fridge. It seems that more things in the fridge the better it will stay cool. Not as much dead air.

Stay cool.
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Old 06-29-2022, 03:47 PM   #5
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I wonder if this is why the left the space above the fridge in the 2022 FC 23 CBB almost entirely empty. I had been considering trying to make use of that space, but this makes me think it's better to let it be a vent space.
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Old 06-29-2022, 04:24 PM   #6
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Hi

Our trailer fridge can say 32 on the readout and be 50 in the fridge section. Check things with an IR thermometer if you have any doubts. The compressor fridge in the van never seems to have a problem.

Bob
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Old 06-29-2022, 08:19 PM   #7
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StarKruzer here are some posts you may find helpful as they touch on a hot cabinet and no insulation


https://www.airforums.com/forums/f42...cb-230593.html

posts 11, 14 17, 32, 40, 41, and 43



Bought some lexan and will use the cardboard as a pattern like in
https://www.airforums.com/forums/f28...ml#post2607526

post #6
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Old 06-30-2022, 12:58 PM   #8
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Thanks everyone for your thoughtful replies - I think I may try to start with a couple of 12V fans on the upper door sucking air up and out the side.
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Old 07-01-2022, 05:41 AM   #9
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Just a follow up:

I verified that I have the EXACT same model number as you do, so assuming the unit isn't defective, which is most likely isn't, ventilation is most likely your issue with it. Once you get some air movement through there, you should see a remarkable performance difference...

To add, the first clue is the wall getting "really warm".....that is a telltale sign of improper ventilation.

Let us know how you make out with whatever solution you come up with.
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Old 07-01-2022, 06:28 PM   #10
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Just a follow up:

I verified that I have the EXACT same model number as you do, so assuming the unit isn't defective, which is most likely isn't, ventilation is most likely your issue with it. Once you get some air movement through there, you should see a remarkable performance difference...

To add, the first clue is the wall getting "really warm".....that is a telltale sign of improper ventilation.

Let us know how you make out with whatever solution you come up with.
Thanks - which wall are you referring to? The space above the fridge (I have a cabinet there) definitely gets warm.
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Old 07-01-2022, 08:24 PM   #11
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StarKruzer, take a read of post #7 above on 6-29-22 ... click on the top link and post 11 as a start. The very warm (bordering on hot) to the touch cabinet top was my first indicator too. Lots of moving parts here but all boils down to the hot air not being pulled out and over the condensing fins by the fans and settling in my 2" gab above the refer.


I wasn't interested in pulling the refer just to install the insulation per Dometic spec that JC didn't provide for, so I sealed it off with some thin metal sheeting to deflect the air out to the fans.
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Old 07-01-2022, 08:55 PM   #12
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Thanks everyone for your thoughtful replies - I think I may try to start with a couple of 12V fans on the upper door sucking air up and out the side.
Good starting point. If your trailer has a chimney leading to a roof vent, then a fan inside the chimney blowing up would be very good. Up is where hot air wants to go.

It is not difficult to eliminate dead air space beside and above the fridge with insulation, and that will help too.
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Old 07-02-2022, 04:56 AM   #13
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Thanks - which wall are you referring to? The space above the fridge (I have a cabinet there) definitely gets warm.
You can/will feel the heat on the adjacent wall next to where the fridge lives depending on the layout of your trailer.

In my case, the wall with TV attached next to it was very warm before I sorted out my heat issues.

But here is a thread on what I did to replace my stock fan with two ultra quite fans with higher CFM to keep the fridge cool.

Here is my thread:

https://www.airforums.com/forums/f37...ge-196252.html

It is a good starting point and might provide some pointers on how to solve your issues. As mentioned, if you have a heat chimney, you want to force it out by using fans.

Let us know how you make out.

Chris
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Old 07-02-2022, 05:26 AM   #14
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I went a different route with fans than many. Instead of trying to move the air through the cabinet with fans in the chimney or door, I got a pair of fans which point directly at the fins on the cooling unit and move a lot of air through them. Combined with the electronic fan control board, so far I'm quite happy with the result.

Here's what I'm using: https://rvcoolingunit.com/2-Condense...-P5819605.aspx

I like that I can set the on/off temps for the fans easily so they don't run all the time, and that I can change the temp settings for different times of year.
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Old 07-02-2022, 09:43 AM   #15
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Lots of good advice here about fans, so I won't post pics of my fan setup. But another thing to understand is that the temp knob actually operates two separate thermostats, one for 110VAC operation and one for propane. I wasted a lot of time and did some unnecessary work before I figured out that they were not set the same. My basic settings are #3 for propane and #6 for electricity. You need to do a multi-day test with the refrigerator full of bottled water. Find the setting that freezes the top compartment but not the lower, and do it for both electric and propane. Then you know where to set it.
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Old 07-02-2022, 11:28 AM   #16
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Originally Posted by richard5933 View Post
I went a different route with fans than many. Instead of trying to move the air through the cabinet with fans in the chimney or door, I got a pair of fans which point directly at the fins on the cooling unit and move a lot of air through them. Combined with the electronic fan control board, so far I'm quite happy with the result.

Here's what I'm using: https://rvcoolingunit.com/2-Condense...-P5819605.aspx

I like that I can set the on/off temps for the fans easily so they don't run all the time, and that I can change the temp settings for different times of year.


Richard, I was already so far down the road from toe OEM ~ POS Rodale freight train conversion to 2X SilenX EXP76-18 (18 dba /90mcfm) with the Fluid Dynamic Bearings all of which translates to efficiency and quiet operation. Then I saw the fans in your pic and discovered rvcoolingunit.com & David. Very nice product I suspect and likely highly efficient.
I have tried covering all the cooling options bases but the 2” uninsulated void above the refer in the refer cabinet that came to my attention when either the stat wire crimp or the stat itself failed, and the fans stopped on a pushing 100 day. I wasn’t even aware of the void there!
I’ve discovered a few things on this quest for a cold refer that can maintain in warmer territory. First is JC didn’t do us any favors. Lack of insulation aside, my top exterior opening really should be at least an inch higher. As other have posted it’s not so much how much hot air is exhausted, but how much of that hot air passes thru the condensing fins and not having a place to settle in the cabinet inc. the cabinet void above the condensing fins.

Seconds is that I realized that some exterior compartments and larger than others. I can’t remember what our back of refer to skin of compartment dimension is, but looking at Kittmaster’s install (Very nice design and result Chris !!), his is enormous. My dept allows for only the depth of the condenser fins, and it is high in the compartment. If I remove the rubber edging on the opening, the top edge and the skin and the fins are very close if not offset to the fins a higher than the skin’s edge. CFM aside, this makes it harder to pull the air thru vs just out. Certainly made sealing off the refer top void with thin metal a critical improvement and god insurance

As noted in my links, the smaller (42 cfm??) horizontal fan didn’t help as much as my cardboard mock-up that controlled where the exhaust flowed and exited. I’ve never been in the 0 freezer & /low 32 refer range on a hot day before and so quickly. So my next step will be a lexan replacement of the mock-up. One other thought inspired by the above comments, I think I’ll be moving the smaller fan up so it is almost to the condenser fins as I think/hope that it will help force more air vertically thru the fins.

Apologies for the lack of brevity, but hopefully we'll all figure out the idiosyncrasies of our TT's and can sit back with a cold one in hand.

Like my old neighbor (the proverbial rocket scientist at Aames) at Sea Ranch used to say about their design meetings...No laughing at suggests from others as you never know what inspiration might be culled from that comment.


Happy Trails

p.s. thanks Richard, I just realized you were the poster for the RVCOOLINGUNIT.com lead! Thanks
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Old 07-02-2022, 11:17 PM   #17
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Out if curiosity, if the problem is removing heat from the area surrounding the fridge itself, wouldn't I see colder Temps after driving at 60 mph for 4 hours as long as the chimney and vent are unobstructed?

In my case, the dometic unit appears to have no fans at all. It seems heat dissipation is purely passive updraft venting

At 100゚ outside, I am lucky to get 9゚ in the freezer And 37゚ in the refrigerator With the interior temperature at around 72゚.

Will a couple of fans installed in the exterior compartment really make that much difference?

David
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Old 07-03-2022, 08:28 AM   #18
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David, I'm not sure of your model but 9/37 in 100 heat to me is workable. Milk is safe and beer is cold. Could it be improved upon with fan? Possibly. I'll let others with roof exhaust systems answer that. I'll look for a thread that addresses both.

However it should be noted, this thread is heavy on the 2 side vent systems that fan design is oriented so that exhaust assist is out vs up thru the roof. I would expect that your updraft w/o a fan is pretty efficient and OTR road draft would improve on that.

Personally I think the roof vent is the better design but seems more common on longer units. My buddy with a FC 25RB has a 2 side vent system and the smaller 3.5" horizontal fan. Most smaller units have the 2 side systems.

In our 20 the level of the condenser fins in relation to the opening is not optimal so it needs a (vertical) fan (s) assist. Our exterior cavity is also more shallow than others, leaving less room for any deflector to effect the flow up, THRU the fins and out as there is a 2" void above the fins. With out the fans (as I noted above and in the other thread), exhaust draft and cooling ceases to exist.


Maybe a search would produce a better thread, and seemingly this started as a fan noise elimination thread, but drifted as thread to in all sorts of solutions with fans, both in updraft and side draft situations.


https://www.airforums.com/forums/f42...lly-11811.html its a long and old thread but maybe will answer your question.


Happy Trails
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Old 07-03-2022, 08:31 AM   #19
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Originally Posted by davidlbriggs View Post
Out if curiosity, if the problem is removing heat from the area surrounding the fridge itself, wouldn't I see colder Temps after driving at 60 mph for 4 hours as long as the chimney and vent are unobstructed?

In my case, the dometic unit appears to have no fans at all. It seems heat dissipation is purely passive updraft venting

At 100゚ outside, I am lucky to get 9゚ in the freezer And 37゚ in the refrigerator With the interior temperature at around 72゚.

Will a couple of fans installed in the exterior compartment really make that much difference?

David
Next time you have a chance.......go and stick your hand/fingers on the heat fins and tube exchangers....after you burn your fingers, you will quickly understand why a forced airflow solves the problem.

You're assuming the Venturi effect totally drafts out the heat from the trailer, but if you notice when you get into the trailer after you stop....what is the internal temp of the trailer....80 degrees? That coupled with a closed space that is OUTSIDE THE DESIGN SPECS of the fridge itself...all of that adds up to major inefficiency of removing the heat off the fridges fins and heat exchanger.

If you look at the fridges owners manual, you will also see it provides an electrical options for TWO fans that can be controlled by the fridges electronics which is unused by Airstream for whatever reason. The default setup by Airstream is the minimum effort based on the installation metrics that Dometic says to apply.
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Old 07-03-2022, 08:58 AM   #20
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Originally Posted by davidlbriggs View Post
Out if curiosity, if the problem is removing heat from the area surrounding the fridge itself, wouldn't I see colder Temps after driving at 60 mph for 4 hours as long as the chimney and vent are unobstructed?

In my case, the dometic unit appears to have no fans at all. It seems heat dissipation is purely passive updraft venting

At 100゚ outside, I am lucky to get 9゚ in the freezer And 37゚ in the refrigerator With the interior temperature at around 72゚.

Will a couple of fans installed in the exterior compartment really make that much difference?

David
Short answer: yes. Long answer: probably.

All propane fridges will struggle over 90 degrees. At 9 in the freezer and 37 in the fridge, you are doing very well.
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