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Old 05-24-2018, 06:51 PM   #1
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Dometic 3962 refrigerator

Iíve 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. Iím new to RVíing so I donít know if my issue is an issue or not.

We have noticed when traveling with the refrigerator on ďgasĒ 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. Iíve 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 Iíve listened at the exterior vent door and can hear the roar of the burner when stopped at rest stops. Iíve 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 ďqualityĒ of the flame. I can see it is blue, but I canít see anymore than that without some more dismantling.

So Iím at a loss. Is a temperature gain like this normal while traveling?
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Old 05-25-2018, 06:44 AM   #2
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Reconnect your fans they keep the air moving up over the coils if you didn't have enough 12V the frig wouldn't run on gas at all. Air movement may be the problem here. If the frig works fine while parked but not when in motion I would think you may be getting a positive pressure in the frig chimney. A test if you could do it would be to run your frig on 120V with your generator while traveling if it does the same thing then it is air flow. Now how to fix it if air flow is the problem, I would make a faring for the front of the chimney that would cause the air to move up and over creating a low pressure area drawing air across the coils and see if that solves the problem. Good luck let the forum know what you do to fix the problem
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Old 05-25-2018, 06:57 AM   #3
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We have the same refrigerator in our Wildcat and had similar problems. After numerous attempts by the dealer to repair it, they finally changed out the circuit board and it seems to work fine now. He said that our problem was that the board was bad and kept telling the fridge that it was at the correct temperature even when it wasn't. This made it shut off. Because it was under warranty they had to change the thermistor first, then something else, and so on. Not saying that this is your problem but that was ours with the same fridge. Good luck because I know how frustrating it is.
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Old 05-25-2018, 07:54 AM   #4
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Your fridge is in the sidewall, and it's in the worse place possible for updraft airflow when moving.

How many fans did you add and how are they positioned?

I think the negative pressure generated by the airflow from the nose when moving right at the fridge lower grate is causing a reverse draft across the fridge cooling unit and therefore causing it not to cool properly.

You can install enough fans to overcome that effect.

If you want to test my theory, you can temporarily add a "scoop" to the back of the lower fridge vent to force air into it when moving and see if that improves the cooling when moving.

You could use a piece of cardboard and some gorilla tape to make one if you wanted to. It'd only need to be 3" or 4" wide and as long as the grate is tall to work. I think the front edge would only need to stick out a couple of inches. Imagine the vent hood exhaust cap turned vertical facing into the wind to see what it should look like.
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Old 05-25-2018, 08:18 AM   #5
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We both agree its airflow I assumed it was a standard installation should have looked it up good call BR
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Old 05-25-2018, 02:17 PM   #6
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Thanks for the replies - I never thought about an aerodynamic issue - good point both of you. I reconnected the fans once I found disconnecting them had no effect.

However, my fridge is not a sidewall installation any more than any other fridge. It has a lower intake on the side and the upper vent exit in the roof, (see picture). It is near the front of the trailer roof at the beginning of the V so it is entirely plausible that the aerodynamics are different from usual.

I installed 4 low speed fans, 46 ft3/min, so with all 4 running Iím pulling nominally 184 ft3/min through the vent stack. They are installed at the roof vent, see pic.

Based on the replies, I think my next steps will be:
1. Use a fridge thermometer to verify internal temperature vs the built in meter on the fridge. The freezer definitely keeps ice cream frozen so I believed the meter - but it makes sense to verify. Iím on the road right now and have been unable to find the kind of thermometer I want and Amazon doesnít deliver to a moving target LOL!
2. If the meter checks out. Build and try various ďfairingsĒ in front of the roof vent to create low pressure area.
3. Source high speed fans and/or temporarily install some fans at the wall vent to push air up from below and see if that improves the moving situation.

It is all still under warranty so if ď1Ē doesnít check out my dealer will definitely be doing some work. Heís definitely going to be asked about it regardless.
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Old 05-25-2018, 02:42 PM   #7
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Quote:
Originally Posted by Bama Rambler View Post
...If you want to test my theory, you can temporarily add a "scoop" to the back of the lower fridge vent to force air into it...

...It'd only need to be 3" or 4" wide and as long as the grate is tall to work. I think the front edge would only need to stick out a couple of inches. Imagine the vent hood exhaust cap turned vertical facing into the wind to see what it should look like.
Being a Porsche guy, Iím thinking GT4 intakes. Itíd be the sexiest looking Windjammer ever. . More seriously though I would think other 3008W Windjammer owners would be having the similar issues if it was aero dynamics alone.
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Old 05-28-2018, 03:33 PM   #8
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Other 3008 owners may be having the same problem. Maybe they're not driving as much as you do or maybe they're tow vehicle isn't the same and therefore affecting the aerodynamics differently.

I like the GT4 intakes. You may start a trend if you put something like that on your unit!
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Old 05-31-2018, 09:59 AM   #9
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Considering aerodynamics further what thoughts does anyone have about this theory...

My condensate hose sticks out 3Ē or so from the lower wall vent (in the picture above). I sometimes see water on the wall of the trailer after weíve been in motion for a couple of hours. Could the air flow across the end of the tube (Bernoulli Principle) be causing sufficient low pressure to pull the cold air out of the refrigerator over time. We would never feel a vacuum in the fridge because as soon as the air flow past the tube stopped, air flow in the tube would reverse until the pressure gradient is equalized.

Itís crazy I know... I could cap the tube for travel and test the theory quite easily.
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Old 05-31-2018, 05:06 PM   #10
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Further update: Sitting in the driveway the additional refrigerator thermometer is within 1 degF of the Dometic panel gauge, so I believe the fridge really was heating up during travel.

I have higher speed fans in hand and will be installing them this weekend. Approx 71 CFM, Iíll wire them in pairs so I can pull 142 or 284 CFM across the coils.
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