Hot weather refrigerator performance

[Merlin]

I'm hoping to resurrect this old thread rather than starting a new one... Had problems with my fridge holding temperature in the AC electric mode this weekend. When the fridge was on propane everything was great, 35 deg on the display. Set the trailer with my trusty level and switched to electric. Three hours later and I reached in to make dinner. Everything didn't feel all that cold. Temp was at 57deg. I switched back to propane and the temp started to drop. I tried electric again and it started to creep up. I came home and down loaded the trouble shooting guide. Being an HVAC-R engineer, I decided to dig in. I have a 2015 21RBS The Fridge is a Dometic RM3762LBFX. Two doors. I Ohmed out the electric heating element and checked all the fuses and voltages. All Good... There is one little computer tower fan located between the upper and lower exterior vent. It is cycling on temperature as it should (loud and annoying). I decided to pull the panels ad set up my blue blower squirrel cage blower and crank up the airflow over the outside coils. Outdoor temps were in the high 70's low 80's. Final conclusion as of tonight is the same as most have stated, the unit runs great on propane and only will function on electric when outdoor temps are below 70. I plan to swap out the little fan with two high velocity QUIET fans. There are mounting holes already there, but there is only one fan. I also plan to make a shroud similar to the one pictured in this post and see if it helps. It seems like the units that vent through the roof don't have these issues as much. FWIW the freezer worked fine on AC but the fridge just wouldn't keep up. I will also inspect the gasket on the door and report back. The only good news is that these units don't use much propane. My gut tells me that I will be running it on propane 90% of the time. Either way that annoying fan has to change! So far I am not very impressed with my dometic appliances. My old camper had a Norcold that ran like a champ in either mode. Any inputs or experience with this is greatly appreciated. Thanks everyone.

Have you disconnected the door frame heater? Those 2 door models apparently have an energy-sapping frame heater to dry out condensation/frost and it might help to disconnect that wire. There's a photo of it on this forum. As others have noted, on AC the fridge takes forever plus a day to cool prior to a trip. On propane it's a few hours. I think the heating element is undersized for what it has to do. In these Dometic refrigerators, are there 2 heating elements, one for AC and one for DC? If not, and everything is run through the DC element, that might explain the poor performance. I'll go check the parts diagrams for mine and see.

[Capt J-rod]

Ok, After some deep internet research LOL, I have decided that I need to insulate the airspace above the refrigerator. Next I will build an air scoop that forces the air from the top of the fins to the top of the exterior vent. I plan to replace the fan with two quiet fans, and bend another piece of metal to force air over the coils. I suspect that the temperature control switch is not coming on soon enough. Most of the info I have gathered is from large RV's that have a fridge in the slide, forcing the mfg to use the side mounted vents. Apparently the roof vented models are much better at cooling. I will post later to say whether or not this helps. I also suspect that the door gaskets are not sealing up perfectly. This seems to be very common with dometic side vented refrigerators.

[Capt J-rod]

RE Merlin, Yes I disconnected the door heater. I also cleaned all the grounds as they had some mild corrosion. Needless to say I'm not impressed with these units. I just made another post, but I suspect the thermal switch for the cooling fan is coming on at too high of a temperature. This model is either 120V AC or propane. I already Ohmed out the electrical element @42 ohms. The manual wanted 44 +or - 10% so I am good there. I do think you are right that the electrical element is too small for the size of the fridge. That explains why the freezer stays cold but the fridge gets warm. The freezer pulls too many btus out and there is nothing left for the fridge. The propane has a lot more Btu's for the cooling system. I think if I can refine the airflow to the back of the unit it will help it a lot. There are mounting holes for a second fan, that should help some. I also might make a bypass switch to these fans for hot days when I'm plugged in to just let them run full time. I can understand the reason for LL picking this unit, one less hole in the roof. I just think it is sad to have to heavily modify a $1200 refrigerator to make it cool food. The fridge cycled between electric and propane since Thursday and continued to fail on electric this afternoon. If and when I fix it I will post the solution. That's what makes this site great!

https://bryantrv.com/docs2/docs/Service%20Manual,%20RM3762%20&%20RM3962.pdf

Page 24 does a half assed decent job of explaining absorption cooling for us geeks. It would have been nice had they actually put the letter that they reference in the description on the diagram though!

My model is not in this Pdf, but they seem pretty worried about the airflow... Our fridges are not installed like this!

http://bryantrv.com/docs2/docs/dometicventing.pdf

[Capt J-rod]

I'm adding my update to help the thread and others... I spoke to tech support at dometic. I will be fabricating a louver to help manage airflow. I will also add a second fan to increase the air over the condenser. Finally I ordered a new thermostat for the cooling fans. The range to the two door thermostat is on at 150degrees, off at 120 deg. The part for the single door fridge is on at 90 off at 120. this will bring the fans on sooner before the heat builds up. Any airspaces above or beside the unit greatly reduces the performance. Finally I was advised to inspect the weld on the heat exchanger for the electrical element to make sure that good heat transfer is happening. Once I get this done I will report to help close out my issues. This is probably long winded, but hopefully it will help someone in the future. The part number for the lower thermostat is #3313470.095.
The biggest downside for the second fan and stat is that it will hurt our boon dockers who are off grid.

[Merlin]

I'm adding my update to help the thread and others... I spoke to tech support at dometic. I will be fabricating a louver to help manage airflow. I will also add a second fan to increase the air over the condenser. Finally I ordered a new thermostat for the cooling fans. The range to the two door thermostat is on at 150degrees, off at 120 deg. The part for the single door fridge is on at 90 off at 120. this will bring the fans on sooner before the heat builds up. Any airspaces above or beside the unit greatly reduces the performance. Finally I was advised to inspect the weld on the heat exchanger for the electrical element to make sure that good heat transfer is happening. Once I get this done I will report to help close out my issues. This is probably long winded, but hopefully it will help someone in the future. The part number for the lower thermostat is #3313470.095.
The biggest downside for the second fan and stat is that it will hurt our boon dockers who are off grid.

Thanks for the continuing info. My fridge has no fan and needs a couple. I bought the fans and with your thermostat number reference I'll be all fixed up. I'm putting in an on/off switch too, so when I need to conserve power I can power off.

[gbpack]

Here's a pic of the sun shade we devised to keep the sun off of the refrigerator section of our trailer. Works really well and helps keep the fridge much cooler when that side of the camper gets a lot of sun. We just bought a 3' x 6' sunshade and I installed some anchors to the top edge of the trailer. We then used a couple of small caribeaners to connect the shade to the anchors and then just used rope and stakes to tie down the bottom part of the shade. Our fridge is one of those that has the automatic fan built in, but this sun shade really helps to supplement that by keeping the fridge portion of the backside of our trailer cooler, which helps keep the temperature in the fridge lower. Even with outside temps in the 90's and full sun on that side of the trailer, the fridge temp stays in the high 30's and the fan doesn't have to work as hard (or long). Very easy and inexpensive mod.

[Capt J-rod]

It appears that your fridge vents through the roof. I think that the shade would restrict the airflow on the top side vent. I am rather disappointed by this whole issue. It wasn't the best design for a refrigerator, but it wasn't the best install and they didn't install it per mfg specs. I respect the idea of one less roof penetration, but not at the cost of a non functioning refrigerator. UGHHHH!

[gbpack]

It appears that your fridge vents through the roof. I think that the shade would restrict the airflow on the top side vent. I am rather disappointed by this whole issue. It wasn't the best design for a refrigerator, but it wasn't the best install and they didn't install it per mfg specs. I respect the idea of one less roof penetration, but not at the cost of a non functioning refrigerator. UGHHHH!

The top of the shade doesn't impair the vent or impede the airflow. It doesn't get up that high. So far this mod had been working well with the fridge remaining cooler and the fan running less.

[mojospeople]

OK, re-resurrecting this thread. I can start a new one if you prefer but it seems this one has the most/best troubleshooting info and makes it a good spot to continue the discussion. I have read and re-read many threads about the 3 way fridge performance and have now installed 2 fans below the exterior fins. They are working as expected when the temp is above 84 degrees although I might have them wired to always on because they run even if the fridge is off. I can work on that later but first.....MY FRIDGE IS STILL TOO HOT!

What steps to take next? This morning the outside temp is 80 degrees, fridge is on LP set at the coldest temp setting and has been running for a couple of days with outside temps between 70 and low 90s. The back of the fridge is shaded all day in our driveway. Interior fridge temp this morning is 50 degrees. The freezer is fine.

During the fan install I confirmed that the baffle appears to be installed correctly per the manual. I had to cut it and remove it to install the fans but then reinstalled the piece I cut out (it ain't pretty in there!). I can feel the warm air coming out the top vent.

Question: for our model RM2554 in the operating instructions no where does it reference the interior thermistor that is attached to the cooling fin. Does it's position on the fin help control temp settings? In reviewing the manual just now I see it is mentioned in the troubleshooting for if the fridge is too cold then this thermistor may not be attached and centered. Maybe I'll take it off today and see if the temps drop.

So right now my next option is interior fans but it seems I should be getting better cooling now and I'm thinking either something is wrong with the unit or I'm just completely missing something here. Help!

[GrampaKilt]

Ah, the absorption fridge saga! I have done all the mods suggested herein (except the lovely sunshade idea) and still find performance only marginally improved in hot weather. To control an inside circ fan, I installed a temp sensor in the fridge 'ceiling' just in front of the freezer door. It reads in the 70's, even low 80's (with the door closed) during hot days, on propane to boot. (It is accurate since I tested with my body temp.) I remain confused (alas, an ongoing state of mind) since the food was cool but not cold. Maybe as the air cools in the fridge, lingering hot air gets trapped up there?? But why doesn't the circ fan mix it up? The best I got at night (ambient temp 50) was 55.

My next step is to place a thermometer in the main fridge compartment. Depending on what I find, I'll re-route the sensor there. If the seeming lack of hot air forced out of the rear top vent is any indication, the placement of my large computer fans is amiss. https://aluminumcamperforum.com/index.php?topic=866.0 I'd really like to get some robust air flow; anybody try a small squirrel cage fan? Also, I note some recommend air flow over the condenser lines (those pipes that zig-zag upwards)-meaning fan is installed in the lower vent vs over the cooling fins. Comments?

I sometimes wonder how much air flow is enough during warm weather. Anybody try pushing air up the rear of the fridge with a 'real' ie. household fan? I wonder how long the fridge will last before I get the chance to install a marine compressor unit...LSW willing?! GK

[Merlin]

In my experience, an interior fan helps with evenness of temps inside more than it helps with overall cooling inside. Try the thermistor placement change, but spend most of your time outside. Getting good airflow on the external fins will help the most, as will adding any extra insulation you can fit in on the sides and top of the fridge. If the unit has changed in its ability to cool it's certainly possible there's a leak.

And, maybe a good question...are you sure the burner is clean and you have a good flame?  The refrigerator at my cabin would get rust in the "chimney" that would fall down on the burner and almost snuff it out. I had to take the inspection cover off the burner and blow the junk out of the supply pipe and off the burner every year. It wouldn't surprise me to find the rough life of an RV fridge leading to the same problem.

[mojospeople]

OK so both this morning and yesterday morning fridge temps were in the low 40s and by late in the day they were mid 50s. Ambient temps between 70 and 95. Making progress. This morning I turned off the fridge and tonight I will pull the shroud off and clean the flue and burner. It doesn't seem very dirty in there compared to other (working) units I've seen but I would be remiss if I didn't try it. It's only 18 months old but it does sit outside year round.

We head out to camp Wednesday for 4 days and hoping we can keep our food cold enough to avoid food poisoning! I think I will pre-cook some things so I don't have to worry as much about them. Or maybe I'll just put meats in the freezer since it is cold. I detest the thought of another weekend using a cooler when I spent thousands to be able to glamp vs camp!

[DavidM]

What is the freezer temp? I think all of the cooling coils are in the freezer, at least on a single door model and maybe you aren't getting enough heat transfer from the fridge to the freezer.

[Apollo]

The fridge in my 2016 21BHS actually runs OK on electric but doesn't cool good on propane.

EDIT: Upon further inspection I found a piece of insulation blocking part of the exhaust vent for the propane flame, once this blockage was cleared the fridge works perfect.

[GrampaKilt]

I found this absorption fridge website that appears to have some veracity. https://www.arprv.com/rv-fridge-fan.php (That said, they tilt towards some paranoia regarding fire potential..)

One comment resonated with me. The point of external fans is not to remove hot air, but to increase/create air flow. Therefore, they recommend a fan at the lower and upper vent and sell a 120 mm ball bearing centrifugal/squirrel cage variety that pushes 25 cfm. The fan runs at relatively a relatively low 1800 rpm and draws only 0.3 amps. I like the fan, but cost is steep @$30USD.

They say the fans are custom spec'd. I can vouch for that. After a long search, I got close (at 1/3 the price), but still only found 120mm or so centrifugal fans that rotate much faster and take twice the amps or more.

If I buy the cheaper fans, add a (resistance) controller to reduce rpms, then according to Ohms Law, I would reduce amps, right? Or am I perplexed (as usual)...or just too darn cheap? GK