Refrigerator Improvement Desired - Fiberglass RV


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Old 04-29-2009, 01:33 PM   #1
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We just got back from a great time at the Eggscursion in Townsend TN. Once again, I was reminded about the marginal cooling of the 12V system in the Dometic 3-way fridge. The 110V system is slightly better, but still somewhat marginal in hot weather. I recall previous threads on this topic that described three possible routes for improvement: improve the duct work on the back of the fridge to help with heat flow, add a 12V fan to help push the heat out the vent, add a 12V fan inside the fridge to improve circulation past the fins. After a quick search, I can't find them. Note to self: learn to better use the search function. I'm interested in improving the duct work and maybe adding the 12V external fan. Some questions before I go further: do these mods really help when going down the highway with 60 mph air blowing past the side of the vent grills? Has anyone considered reconfiguring the vent grills to actually benefit from the air going past? Finally, while I recall a great posting showing the desired flow path for moving the hot air up and out (which I can't find now), how do I get access to this area? It looks like I'll need to drill out the rivets and remove the upper grill to get in there. I don't mind doing that, but I want to be sure I need to do it and that I'll likely gain some improvement for my efforts.

Thanks!
Parker
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Old 04-29-2009, 01:48 PM   #2
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Here's one: http://www.fiberglassrv.com/board/in...howtopic=29991
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Old 04-29-2009, 03:14 PM   #3
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That's it! That includes the entire discussion with links, so I should be set. And it does appear I'll have to remove the upper grill to make any improvements. I never did see an answer to the question about where to put the reflective material, but I think it will be obvious when I get in there. I don't plan to remove the fridge during this exercise, so that may limit my choices somewhat.

Thanks,
Parker
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Old 04-29-2009, 03:55 PM   #4
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I know it's probably not what you want to hear, but I did all the fan and baffle tricks and didn't see that much of an improvement with my old unit. You should probably test it with a small fan and temporary baffle at home to make sure your unit isn't just too weak before ripping anything out. As to 12V efficiency on the road, well, it's not really efficient to start with, even in the best conditions. I could be wrong, but I'm thinking that no small 12V fan can really come close to air circulation caused by a moving trailer.

There is one more thing worth trying that isn't mentioned in that past thread though. Since heat goes up, I'm thinking of adding insulation and reflective material in the space under the fridge. It would make sense, given all the radiating heat rising from the roads into your fridge. I'm not holding my breath, but who knows.
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Old 04-29-2009, 04:13 PM   #5
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I know it's probably not what you want to hear, but I did all the fan and baffle tricks and didn't see that much of an improvement with my old unit. You should probably test it with a small fan and temporary baffle at home to make sure your unit isn't just too weak before ripping anything out. As to 12V efficiency on the road, well, it's not really efficient to start with, even in the best conditions. I could be wrong, but I'm thinking that no small 12V fan can really come close to air circulation caused by a moving trailer.

There is one more thing worth trying that isn't mentioned in that past thread though. Since heat goes up, I'm thinking of adding insulation and reflective material in the space under the fridge. It would make sense, given all the radiating heat rising from the roads into your fridge. I'm not holding my breath, but who knows.
I'm sure every little bit helps, but it may still be insufficient to see a measurable improvement. I'm sorry to hear that you didn't get better results. I am a little surprised that someone hasn't come up with an ejector to put on the side of the trailer that would pull air up through the hot air vent. I can just see all the marketing possibilities for some cheap plastic gizmo, just there for the taking! Of course there would have to be some way to make it revert to the chimney function while stopped. And we can't have something that would somehow direct rain into the vent. Something to think about during my next seven hour drive down I-75 to Tennessee!

Parker
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Old 04-29-2009, 04:30 PM   #6
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Something to think about during my next seven hour drive down I-75 to Tennessee!
I like the way you think... How about a water heater based on a heat exchanger taking the heat from the coils to warm up the water? Like water under the fridge™. Any takers?
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Old 04-29-2009, 10:18 PM   #7
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We just got back from a great time at the Eggscursion in Townsend TN. Once again, I was reminded about the marginal cooling of the 12V system in the Dometic 3-way fridge. The 110V system is slightly better, but still somewhat marginal in hot weather. I recall previous threads on this topic that described three possible routes for improvement: improve the duct work on the back of the fridge to help with heat flow, add a 12V fan to help push the heat out the vent, add a 12V fan inside the fridge to improve circulation past the fins. After a quick search, I can't find them. Note to self: learn to better use the search function. I'm interested in improving the duct work and maybe adding the 12V external fan. Some questions before I go further: do these mods really help when going down the highway with 60 mph air blowing past the side of the vent grills? Has anyone considered reconfiguring the vent grills to actually benefit from the air going past? Finally, while I recall a great posting showing the desired flow path for moving the hot air up and out (which I can't find now), how do I get access to this area? It looks like I'll need to drill out the rivets and remove the upper grill to get in there. I don't mind doing that, but I want to be sure I need to do it and that I'll likely gain some improvement for my efforts.

Thanks!
Parker
Hi Parker,
Have you checked the door seal. If it doesn't seal all the way around nothing you do will make it work well. Heat from the 120v/12v element or the propane burner has to pass unobstructed up through a tube on the back of the fridge. Small spider webs etc. could be blocking this tube. There is also a piece of sheet metal suspended in this tube on a wire hooked over the top of the tube, which creates the correct flow rate as the warm air rises. If it works better on 120v or 12v than it does on propane you might also have a restriction somewhere in the gas delivery system. Take the small tubes off the back of the fridge and make sure there is no blockage. If it is working properly it should form ice cubes in 2-3 hours. I've owned about 10 of these small trailers and only ever had one I couldn't revive.
Bill
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Old 04-29-2009, 10:43 PM   #8
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This isn't true for all RV fridges, but I've looked at the specs for some and generally speaking, the LP mode is the most robust, the 120VAC mode in next and the 12VDC mode is weakest (more to maintain the cold than to actually change it), based on the heat output of each mode to run the refrigeration cycle.

But in all cases, moving hot air out of the boiler area will improve the efficiency. The RVs with the vent stack exit on the roof are off course better than the ones with the exit in the vertical wall, but all would benefit from a small fan to help the process. Some put a switch on the fan, others use a thermostat to control it.

Another improvement would be to put a block across the bottom half or two-thirds of the fridge door inside, so when the door is opened, the cold air inside doesn't 'spill' out and need to be replaced. Could be just a thin sheet of stiff clear plastic.

Also, if possible, some insulation UNDER the fridge to keep rising heat from warming the box.
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Old 04-29-2009, 11:25 PM   #9
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Pete;

Your comments are right on. All we ever use the 12v for is maintenance during driving from one location to another. Fridge is almost never opened, and yet, it barely does the trick. The moment we are set up, on goes the propane. 120v was used to prep the fridge at home. Get an empty fidge to temp, so the night before it could be loaded with already refrigerated components. I think my 120v gave up the ghost again though. It was a bad switch last time.

Another thrick that helps a great deal on those weekend trips, not so much on the long hauls. We freeze two 2 litre plastic milk containers containing drinking water, and keep them on the fridge door. Quick cool drinks and some additional cooling.

Vic
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Old 04-30-2009, 06:22 AM   #10
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If it is working properly it should form ice cubes in 2-3 hours.
Bill,

We've had ours freeze things in the very bottom of the fridge if running on 120V or propane for a couple of days, but seriously doubt we could expect to make ice in 2-3 hours! I'll follow up on your tips. The fridge is five years old, and while the door seems to seal fine, it's easy enough to check before getting into the other areas.

Thanks!
Parker
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Old 04-30-2009, 06:34 AM   #11
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All we ever use the 12v for is maintenance during driving from one location to another. Fridge is almost never opened, and yet, it barely does the trick. The moment we are set up, on goes the propane. 120v was used to prep the fridge at home. Get an empty fidge to temp, so the night before it could be loaded with already refrigerated components.

Vic
Vic,

Your experiences and procedures are very similar to ours. Most of the things we transport are not critical about low temperatures, but 12V operation is still pretty marginal. Like Pete said, in descending order of cooling, it's propane, 120V, and 12V, probably because of the amount of heat they can generate. I took great care in running large wire to power the Scamp system, have good grounding, etc, so that's about all I can do on that end. Hopefully I can make some improvements elsewhere. I can see why folks are tempted to run these on propane while towing. I tried it once, but it won't stay lit while driving. Oooppps....I don't mean to open the propane on while driving discussion. I'll stick with trying to improve the efficiency of the setup.

Parker

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Old 05-02-2009, 05:54 PM   #12
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just wanted to know is it possible to hook the refridge up to a inverter and have it operate on 110 instead of 12/v while going down the road
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Old 05-02-2009, 06:07 PM   #13
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Quote:
is it possible to hook the refridge up to a inverter and have it operate on 110
Link to Per Walthenson's comment on another post
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Old 05-02-2009, 06:33 PM   #14
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Thanks! I hadn't read that string before this. Interesting ideas about running off an inverter, which would allow using the 110V heating element in the fridge, as long as the TV can keep up. I was also interested in reading about the propane experiences while under tow. The times I tried it, the flame blew out. The folks we got the Scamp from said there was some sort of procedure for blocking part of the grill (I don't know if upper or lower) to keep that from happening while in motion. I've never pursued it.

Parker
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