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Author Topic: Anyone's Dometic RM7030 Frige really work on gas?  (Read 6382 times)
TexasBorderDude
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« on: December 05, 2007, 10:03:30 AM »

As a fulltimer I'm trying to assess my travel/boondocking capacity.  I have a Dometic gas/elec frige. that is only marginally effective on gas.  Depending on the ambient outside temp, my freezer ice will melt within a day or several; and the frige contents will be up to 50+degrees in the same timeframe.  I realize that the unit must be level to operate on gas, so I can understand why the gas operation would be minimal while traveling... but I need to determine a  benchmark.  Does anyone have good results operating this (or similar) frige's working on gas?

Thanks,

dg

ps.  What kind of battery life do you get on the electrical operation of the same frige?  I'm not getting much time on my new 8 battery 6volt Interstates on a Trace 2500 inverter.  Only a couple of hours, but that's another topic and I need to document some capacity testing!!!
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« Reply #1 on: December 05, 2007, 10:15:31 AM »

DG,

The thing works the same on DC/AC as it does on gas.  Heat applied to the "boiler".  The gas is , in my experience, much hotter and works so very much better in terms of how cold it gets how fast.  That dc mode is only for traveling with the generator running and nothing more.  The AC mode is for parked in a park with shore power and again, it cannot be supported with the batteries.  At least not realistically.  The inverter will only power this while you have lots of current from the alternator.

You have a problem with your unit.  The only problem you can't deal with is a punctured evaporator so you are in luck there.  Call Dometic to get their take.  A factory authorized shop should diagnose the problem for one hours labor charge and then you can order from Dometic and make the repair.  Might save a hundred or so.  The bright side is you have the best and most reliable refer on the market and it is well supported.  Repair it Bro.

HTH

John
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TexasBorderDude
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« Reply #2 on: December 05, 2007, 10:23:51 AM »


Quote
The AC mode is for parked in a park with shore power and again, it cannot be supported with the batteries.  At least not realistically.  The inverter will only power this while you have lots of current from the alternator.
John, thanks for the prompt reply.  I don't understand why the frige would not operate as any other user of 110 current.  Why would say a microwave operate without
Quote
lots of current from the alternator.
?

Please 'splain!  Thanks...
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« Reply #3 on: December 05, 2007, 10:36:35 AM »

Doyle,
  Your reefer requires a heat source to operate. This heat source is either an LP flame or an electric element. Sounds like your LP flame is not hot enough. Burner may just need cleaned. When trying to operate off the inverter, remember that any electric heating element consumes a lot of electricity. As was mentioned, electric is for when you have a AC (or DC) power source such as shoreline, generator, or alternator producing power.  Your microwave uses power for maybe a minute or two, your reefer uses power anytime the interior temperature is above the reefer thermostat setting.  Hope this helps, Jack
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TexasBorderDude
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« Reply #4 on: December 05, 2007, 10:56:14 AM »

Ahhh!  So the wattage required to heat the electric "burner" is resistive and draws more current than the microwave.... gottcha!  It's a matter of load usage.  Thanks...
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Nick Badame Refrig/ACC
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« Reply #5 on: December 05, 2007, 11:03:20 AM »

Hi Doyle,

Jack is correct about checking the burner tube for a build up of dirt. It's a very common of a problem with RV reefers.

You need good heat transfur from the burner, to the amonia for it to work properly. It's also possible that your burner

orfice is partally clogged and putting out a very low flame.

Good Luck

Nick-
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« Reply #6 on: December 05, 2007, 11:16:37 AM »

Not to belabor this too much longer, butt shouldn't the frige maintain it operation (on ac) with the inverter on while driving with the alternator supplying extra charge?
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« Reply #7 on: December 05, 2007, 11:43:48 AM »

Not to belabor this too much longer, butt shouldn't the frige maintain it operation (on ac) with the inverter on while driving with the alternator supplying extra charge?

Depends on how big your inverter is and how much power the reefer uses. It is when you are boondocking without the engine running that running off the inverter will suck down the house batteries.  Jack
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« Reply #8 on: December 05, 2007, 12:15:58 PM »

Not to belabor this too much longer, butt shouldn't the frige maintain it operation (on ac) with the inverter on while driving with the alternator supplying extra charge?

My experiences are with a friend's S&S... the gas option works MUCH better than the electric.  I believe I read that the AC element is 250 watts.  I can't guarantee this, but I seem to remember reading it on the friend's Dometic.  It's a lot to draw from batteries, but it should work from the alternator / inverter.  Your initial question was about working on gas... it should work much better (colder) on gas than elec.
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« Reply #9 on: December 05, 2007, 12:33:20 PM »

My personal experience on several vehicles is that the gas works significantly better than the electric. Even in ambient temperatures of 100 degrees plus. The amount of gas uses is so small that I never switched from gas to electric even when in a location for a few days that had shore power.

Ir is really a significant waste of power, due to inefficiencies, to operate an inverter from a 12 volt supply, let the inverter convert the 12 volts to 120 volts AC and then use that power to operate the fridge. Much better to operate it off the 12 volt directly if gas or 120 volt power is not available.

Richard
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« Reply #10 on: December 05, 2007, 02:07:29 PM »

If it has never worked well either on gas or electric then it is likely to be badly installed. It is critical to get airflow up the back of the unit and if there is too much clearance between the unit and the wall, the air just flows up the wall instead of past the cooling fins. Baffles need to go from the wall to within 1/2" of the fins to force the airflow through the fins. Vents top and bottom need to be in the correct position and with no free space above the fridge at the back.  Dometic have detailed instructions for installation. 
Poor installation may also be the problem even if it appears to work OK on electric since if the electric element is a bit hotter than the gas flame, operation may appear OK but is really marginal and when it goes on to gas becomes sub-marginal.
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TexasBorderDude
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« Reply #11 on: December 05, 2007, 02:12:52 PM »

Tony, you may be on to the prob.  Do you have a link to the install notes?  Works real well on elec.,  butt there's lots of clearance behind the unit.  Thanks to all! 

dg

Edit:  I found http://www.dometicusa.com/pdf/825122801%20MO-FO%200438%5B1%5D.pdf which prescribes 1 inch MINIMUM rear clearance.  The electric heat element seems to be inside the exhaust flue of the gas burner.  On electric power it is warm to the touch.  I plan to put the frige on gas tomorrow, and compare the heat in this flue. (I already know that on gas, the frost on the fins in the refrigerator compartment  begin to melt within an hour... so I suspect there is less cooling on gas).... will prolly have to go to CampingWorld for a diagnosis.  dg
« Last Edit: December 05, 2007, 02:49:58 PM by TexasBorderDude » Logged

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« Reply #12 on: December 05, 2007, 02:48:42 PM »

As mentioned, if it works well on electricity, your problem is most likely minor.  This is an absorption frig and runs on heat.  Since the gas flame puts out more heat than the electric heating element, it runs best on gas.  Therefore, it is clear that your gas flame is too weak.  The "burner" which is barely more than a large pilot flame, could be clogged.  I have heard that there is even a particular species of spider that likes the smell of propane and sometimes moves into the orifice.  Check/clean the orifice, make sure that the gas supply is fully on and unobstructed.  This is hopefully the simplest problem you will ever have to deal with.  If it is a 3-way frig, then it can run on 12v when gas and 120v are not available.  However, that function is just for supplying minimal cooling while running down the road; it does not work nearly as well as 120v or gas.  You could run it on 120v through your inverter while traveling if it is within the capacity of your alternator to handle along with whatever else you want it doing.  But there is no real reason to run it off your batteries through the inverter while parked; that's what the gas is for if your are without shore power, and it works great.
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« Reply #13 on: December 05, 2007, 02:56:55 PM »

As mentioned, if it works well on electricity, your problem is most likely minor.  This is an absorption frig and runs on heat.  Since the gas flame puts out more heat than the electric heating element, it runs best on gas.  Therefore, it is clear that your gas flame is too weak.  The "burner" which is barely more than a large pilot flame, could be clogged.  I have heard that there is even a particular species of spider that likes the smell of propane and sometimes moves into the orifice.  Check/clean the orifice, make sure that the gas supply is fully on and unobstructed.  This is hopefully the simplest problem you will ever have to deal with.  If it is a 3-way frig, then it can run on 12v when gas and 120v are not available.  However, that function is just for supplying minimal cooling while running down the road; it does not work nearly as well as 120v or gas.  You could run it on 120v through your inverter while traveling if it is within the capacity of your alternator to handle along with whatever else you want it doing.  But there is no real reason to run it off your batteries through the inverter while parked; that's what the gas is for if your are without shore power, and it works great.

Great point Lin. I remember having to use an air hose and clean out the gas igniter/jet assembly every year.

Richard
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« Reply #14 on: December 05, 2007, 03:11:13 PM »

Meeesoooo (me so) confused!  It's dark now in Florida, so for drill I unplugged the frige and watched as the gas kicked in.  A real virgorous flame appeared (about twice the size of my toothbrush!) butt it ain't enough to cool the unit.  What's next?  Check the electronic board?


ps.  used the ubiquitous air hose earlier!
« Last Edit: December 05, 2007, 03:19:18 PM by TexasBorderDude » Logged

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