Dometic 3962 refrigerator

[Windjammingnc]

Originally Posted by MR.M

Looks can be deceiving, let us know if anything changes with the new regulator / by the way did the tech do a test of the gas pressure ?

Tech did not test the gas pressure.. The dealer did note that the fridge did not have any insulation between the sides of the fridge and the wall (about 1" gap). Considering the ambient temperatures recently have been in the upper 80's and low 90's while we have been driving, I am sure that has not helped in keeping the interior fridge temps low during travel, especially when the fridge is off.

[Thurman]

While reading all the posts a question came to mind as to the LP gas pressure to the burner being within specs. As "Mr M" stated I agree that at this time having the LP gas pressure checked at or as close to the burner would be a good idea. Not to say that the pressure may read correctly when static checked but you may have a problem with the pressure being properly maintained while the burner is lit. A good technician will know how to check the pressure while the flame is on or better yet do a flow test while the flame is lit.

[MR.M]

Originally Posted by Windjammingnc

Tech did not test the gas pressure.. The dealer did note that the fridge did not have any insulation between the sides of the fridge and the wall (about 1" gap). Considering the ambient temperatures recently have been in the upper 80's and low 90's while we have been driving, I am sure that has not helped in keeping the interior fridge temps low during travel, especially when the fridge is off.

Yep most all fridges have insulation on each side . someone left it out at factory , must have been a Friday afternoon when they built it . would not be to hard to install and the dealer tech should have done that .

[Windjammingnc]

Originally Posted by MR.M

Yep most all fridges have insulation on each side . someone left it out at factory , must have been a Friday afternoon when they built it . would not be to hard to install and the dealer tech should have done that .

Another punch list item I guess - maybe for when we go to the FROG rally next year...



I did discover a positive on my plan to power the fridge via Inverter when traveling. It turns out that the circuit that powers the fridge is shared with the Entertainment Center outlet, bathroom, bedroom and outside outlet. So, when we are dry camping, I can force the fridge to Gas and use the same inverter to power the Television or outside outlet for TV or Fans... We've discovered that there is quite a voltage drop over DC to the 200W inverter I currently have behind the TV in the Entertainment center and having the Inverter co-located with the power distribution panel will help that situation. We will be upgrading to a 500-600W inverter and an Automatic Transfer switch (15Amp).

[rockfordroo]

Originally Posted by Windjammingnc

Another punch list item I guess - maybe for when we go to the FROG rally next year...



I did discover a positive on my plan to power the fridge via Inverter when traveling. It turns out that the circuit that powers the fridge is shared with the Entertainment Center outlet, bathroom, bedroom and outside outlet. So, when we are dry camping, I can force the fridge to Gas and use the same inverter to power the Television or outside outlet for TV or Fans... We've discovered that there is quite a voltage drop over DC to the 200W inverter I currently have behind the TV in the Entertainment center and having the Inverter co-located with the power distribution panel will help that situation. We will be upgrading to a 500-600W inverter and an Automatic Transfer switch (15Amp).

The issue is the distance from the inverter to the BATTERY, not the distribution center. Most distribution centers are 8-10 ft or more from the battery. When boondocking, it's the battery that's supplying the DC, not the distribution center. Put your inverter as close to the battery as you can.

[Windjammingnc]

Originally Posted by rockfordroo

The issue is the distance from the inverter to the BATTERY, not the distribution center. Most distribution centers are 8-10 ft or more from the battery. When boondocking, it's the battery that's supplying the DC, not the distribution center. Put your inverter as close to the battery as you can.

If I was putting a 1000W+ inverter then I would agree but given that I don't plan to draw more than 400W, I will put it under the fridge where the distribution panel is. The fridge/panel is about 6 feet from the battery (there aren't really any options on placement closer to the battery) and I already am planning to upgrade the wiring from the battery to distribution panel from 8 Gauge to 4 or 6 Gauge.


Thanks,
Paul

[rockfordroo]

Sounds like about the best you can do.

[Windjammingnc]

Originally Posted by rockfordroo

Sounds like about the best you can do.

Thanks for the suggestion though. I attached the floorplan to my previous post that shows the location of the fridge.


I also plan to cut some vent holes and add a quiet 12v fan to ensure that the area under the fridge is able to be vented since between the Converter and now the Inverter, I expect it will get warm under there.

[TJA1]

Thought I’d post an update on this thread. Dealer found nothing wrong just as I assumed he would. They did call Dometic support and were allegedly told that Dometic no longer recommend using refrigerators while moving. They have had a lot of issues resulting from “too much air flow” causing too much efficiency and burning out of components... This sounded like Dealer BS to me, so I e-mailed Dometic myself and was told Dometic have no end customer support desk and all support is through my authorized dealer!

This is becoming layer upon layer of BS!

However, I did find the following thread...3 year old Dometic doesn't work - Page 15 - Airstream Forums

It’s a long read but worthwhile because the OP has tested his fridge cooling system with thermocouples. There’s quite an education in the pages. The meat of the thread is that he ended up adding baffles to his wall vent to reduce the amount of incoming air. This also might lend a little credence to Dometics position on fridge use while traveling.

I’ve bought a vent scoop as discussed earlier but have not installed it yet. I’ll mock up the scoop installation and then remove it. I have a long trip coming up in Sep and I’m going to try the baffling to reduce air flow first. Then I can always install the scoop if I find reducing air flow I is not the cure.

[MR.M]

Originally Posted by TJA1

Thought I’d post an update on this thread. Dealer found nothing wrong just as I assumed he would. They did call Dometic support and were allegedly told that Dometic no longer recommend using refrigerators while moving. They have had a lot of issues resulting from “too much air flow” causing too much efficiency and burning out of components... This sounded like Dealer BS to me, so I e-mailed Dometic myself and was told Dometic have no end customer support desk and all support is through my authorized dealer!

This is becoming layer upon layer of BS!

However, I did find the following thread...3 year old Dometic doesn't work - Page 15 - Airstream Forums

It’s a long read but worthwhile because the OP has tested his fridge cooling system with thermocouples. There’s quite an education in the pages. The meat of the thread is that he ended up adding baffles to his wall vent to reduce the amount of incoming air. This also might lend a little credence to Dometics position on fridge use while traveling.

I’ve bought a vent scoop as discussed earlier but have not installed it yet. I’ll mock up the scoop installation and then remove it. I have a long trip coming up in Sep and I’m going to try the baffling to reduce air flow first. Then I can always install the scoop if I find reducing air flow I is not the cure.

I agree all BS . been running dometic fridges for 30yrs never issues while driving . 4 yrs in my current unit and long travel days from west yellowstone to Fl every yr

[Windjammingnc]

I would post an update. Inverter and transfer switch are installed and made some observations which makes me wonder about trailers with Residential Fridges and Inverters.


With all shore power disconnected, the Inverter was drawing 37Amps (+/-) from the battery (voltage drop to the Inverter was about 1 volt). I had upgraded the wire from the battery to the Cutoff Switch (+) and Chassis (-) to 4 gauge but wire from there (about 4 feet) to distribution panel is still 8 gauge (to be upgraded in the fall).


If I start the engine of the truck, surprisingly the battery draw only drops to 14Amps which means the truck is only able to provide about 22Amps of current which is probably due to the Gauge and Length of wire from the Alternator to the Trailer.


Will be interesting to see if the battery current drops when the truck is mobile and not just idling but this would indicate the over a long drive (6+ hours), the batteries would experience a significant draw-down.


I also plan to observe the temperature of the fridge after the drive on our next trip (Approx. 4 hours) to see if it rises over 15 degrees like it did on gas.


Will post an update.

[Windjammingnc]

Originally Posted by TJA1

I’ve searched the forum looking for a similar situation and so far found nothing.

I have a new 2018 Rockwood Windjammer 3008W with a Dometic 3962 refrigerator, 120V / LP operation. I’m new to RV’ing so I don’t know if my issue is an issue or not.

We have noticed when traveling with the refrigerator on “gas” operation it cools very poorly. Starting the day with air temperatures 75/77 degF ambient finishing the day with 85/87 degF. The refrigerator (by the front panel gauge) starts the day 36/37 degF and finishes the 5 to 6 hour journey around 43/47 degF. Cooling setting is set at 4 (1 - 5 is the available temp setting range, 5 is the coolest). No error codes are shown and the fridge indicates gas operation when 120V shore power is disconnected.

The fridge works fine on 120V shore power. Moreover, it works fine on LP when stationary in the campground. I’ve run it on both for 24 hours and both have maintained temperatures in the 36/37 degF range, even when the door is being opened/closed while cooking.

All this indicates to me that the cooling unit and control circuitry are working properly. On the last couple of travel days I’ve listened at the exterior vent door and can hear the roar of the burner when stopped at rest stops. I’ve also disconnected all the fans that I wired to the 12V supply in case these were drawing down the 12V supply - this step did not result in any improvement. I have not removed all the tin heat shielding so I have not yet assessed the “quality” of the flame. I can see it is blue, but I can’t see anymore than that without some more dismantling.

So I’m at a loss. Is a temperature gain like this normal while traveling?

With the inverter installed for the fridge, on this most recent trip, we started the trip at 40F (fridge set to 3) and by the end of the 4 hour drive, the temperature was at 43F. Once we hooked back up to shore power at the site, the temperature of the fridge was back to 40 with 30 minutes.

So far the inverter mod has been successful and while we were driving, the batteries were only being drained about 8amps.

[Windjammingnc]

Originally Posted by Windjammingnc

With the inverter installed for the fridge, on this most recent trip, we started the trip at 40F (fridge set to 3) and by the end of the 4 hour drive, the temperature was at 43F. Once we hooked back up to shore power at the site, the temperature of the fridge was back to 40 with 30 minutes.

So far the inverter mod has been successful and while we were driving, the batteries were only being drained about 8amps.

Update: On this current trip, we have power hookup and it's hot (90+) and humid with lo little breeze. The fridge is having difficulty keeping the temperature below the mid 40s. It usually gets there overnight but in the daytime, it's in the upper 40s (fridge is set to 5, max cool).

Did the fan mod in the vent stack help?

[TJA1]

Hopefully, my last update to this thread as it appears the problem is solved! 👍. I’ve started my trip out west and so far on two days of travel with the fridge on the sunny side of the trailer in 80 degF plus ambient temperatures the fridge has maintained 33- 34 degF over 5 or 6 hours of traveling after starting the day at 32 - 33 degF. 1 deg rise in 6 hour s is a lot better than 1 deg in 30 min.

The solution was to block airflow to the lower vent! I made a shield from steel sheet to cover the burner/boiler side of the lower vent and made second shield from Reflectix insulation to cover the electronics side of the vent. I put these in right before I start moving and remove them as soon as I’m at the campground.

The clue to what was going on is from the Airstream Forums where one member describes an identical issue to mine. The thread by “Buttercup” is linked below and the two posts by forum member that explain everything are on page 12, post 168 and page 13, post 177.

3 year old Dometic doesn't work - Page 12 - Airstream Forums

Counterintuitive for sure as we all spend time looking for way to boost airflow but in this instance the solution is less flow. Essentially the issue with too much air flow is that the cooling unit piping is super cooled so the ammonia vapor from the boiler condenses in the pipework before the condenser so it cannot do the heat removal where it needs to. The complete explanation is in the thread link above along with all the temperature reading Buttercup obtained from thermocouples all over his cooling unit.

I still operate two fans to pull air up through the roof exhaust vent, the spec on the fans is approx 55 cu-ft/min (ea) so I’m drawing 110 cu ft through the chimney.

Hope this helps you and anyone else who is having this issue. Pictures of the shields and installation below. The edges of the reflectix are wrapped by aluminized tape to add to rigidity and give some additional protection on the burner side.

[TJA1]

Originally Posted by Windjammingnc

Update: On this current trip, we have power hookup and it's hot (90+) and humid with lo little breeze. The fridge is having difficulty keeping the temperature below the mid 40s. It usually gets there overnight but in the daytime, it's in the upper 40s (fridge is set to 5, max cool).

Did the fan mod in the vent stack help?

Yes. With two of the 55 CFM fans running my fridge remains at 32 degF on gas or electricity when stationary using cooling setting 4 on the fridge. There is no need for four fans other than I have a back up. Setting 5 begins to freeze things. As stated in my other update above, on the road with the baffling of the lower vent 33 - 34 degF in transit.

[Windjammingnc]

Originally Posted by TJA1

Yes. With two of the 55 CFM fans running my fridge remains at 32 degF on gas or electricity when stationary using cooling setting 4 on the fridge. There is no need for four fans other than I have a back up. Setting 5 begins to freeze things. As stated in my other update above, on the road with the baffling of the lower vent 33 - 34 degF in transit.

I'll be sure to add some to ours - what size were they?



Also related to temperature - on our last trip, I put a temperature sensor on the second shelf in the fridge and noticed that the temperature was up to 7 degrees warmer than was displayed on the fridge panel - in a few cases, reading 50F. Somewhat concerning.


Hopefully with the fans added and the fridge operating in the mid-30s, the rest of the fridge will be in the safe zone of low 40s. Don't really want to add a fan to the inside of the fridge.

[TJA1]

Specifically my fans are 120 mm (4”)

https://noctua.at/en/nf-f12-industrialppc-2000

They are available on Amazon do a search for:

Noctua SSO2 Bearing, Retail Cooling NF-F12 iPPC 2000

They are industrial rated fans so they are more weather resistant than the more common computer case cooling fans. I made an aluminum frame that clips over the base of the roof vent. Everything is held in place when the vent cover is screwed in place. Note, the fans in the picture were old fans I used to prove the concept and have been replaced by the better fans I linked to.

[Learjet]

I've been dealing with the same issue with my trailer for over 3 years Frig model RM3962RSSX. It's only a real issue for me on the all day trips, then I just stick an ice pack in the frig and live with it. Freezer seems fine as other have said. Never had this issue on an of my other RVs.

I think I will tape up the intake vents on the outside of the trailer next long trip with some wide painters taps...leaving a small section open for some air flow and see how this works.

Having blue painters tape on it ...I will not be able to forget to remove it when parked.

[TJA1]

Originally Posted by Learjet

...
I think I will tape up the intake vents on the outside of the trailer next long trip with some wide painters taps...leaving a small section open for some air flow and see how this works.

Having blue painters tape on it ...I will not be able to forget to remove it when parked.

I considered painters tape. However my experience with using painters tape to protect my track car hood showed it comes off quickly in the rain. I also considered cutting strips of the hard foam pipe insulation to jam in the three vent strips of the cover. Then I worried that these might get pulled out by the slipstream. That was how I ended up with the inside baffling.

However, the painters tape to prove the concept is definitely a low cost experiment. If reducing air flow works for you then consider other ways to achieve the same reduction in flow.

BTW I am now two more days into my trip and success continues, fridge temp 33 - 34 and today the fridge side of the trailer was in full sun for over 5 hours. 👍👍

[pgandw]

Thank you for all your research and the link.

On my previous A-frame (A122 standard height), I had the typical poor airflow problem. When towing at 40MPH plus, on DC fridge performance was good to very good, usually pulling down to below 32 in 3-4 hours after starting at 40. When I slowed down or stopped, fridge temps would rise. Cooling fans were needed when I wasn't towing. The propane flame would blow out when towing, being a continuous run fridge there was no auto-ignition. So had to tow on DC, not propane.

I just replaced the smaller A-frame with a Flagstaff T21TBHW high wall A-frame. The fridge is bigger, has the sliding thermistor for regulation, a small freezer, a DC control board, and a cooling fan installed. I looked forward to towing with fridge on propane so I could be assured of arriving at campsite with fully charged batteries.

On the 1st trip fridge pre-cooled fine, but warmed up noticeably while towing (about 40 minute drive). No check light and boiler was warm which suggested propane was staying lit. Later found thermistor was pretty low, so moved up to top. Cooling at campsite improved after doing that.

Need more data from the 2nd trip this weekend - 2+ hours each way. But I'm thinking I may have to baffle while towing. FWIW, I use a wireless thermometer inside the fridge as my instrumentation. I bought a couple of computer case fans to improve air flow as I did in the previous camper. But it stands to reason if installing cooling fans can improve things significantly when the there is little wind, too much wind can also cause poor performance. Fridge performance has some sensitivity to air flow.

Thanks again for posting.

Fred W
2014 Rockwood A122 A-frame
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan