Which wire is positive? - Fiberglass RV


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Old 07-23-2012, 12:57 AM   #1
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Which wire is positive?

I picked up a used Dometec 3 way fridge with a small freezer comp. to replace the original fridge in my 72 Boler (no freezer). The replacement fridge is virtually the same physical size as the original. I can not make out the model number on the name plate.

On gas operation I understand the unit still has to be connected to 12V DC to operate the controls. It has a blue and black wire exiting the wiring box at the back of the fridge. Which one is positive or does it matter since it's DC voltage? Thanks.
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Old 07-23-2012, 01:48 AM   #2
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Go to the Dometic web site armed with the model number of your fridge. You should be able to find the manual in pdf format.


DC (D--Direct C--Current, AC A--Alternating C--Current) North America AC house current switches direction every 1/60 second. DC doesn't change, the current always flows in the same direction. In many cases if you connect DC up backwards you destroy something.
I don't believe your 3 way requires DC except when operating in DC mode. But the manual will tell you. You might even find the manual in the Document Center on this site, you still need the model number.
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Old 07-23-2012, 06:18 AM   #3
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It is possible that this refrigerator was designed for shipment overseas as well as the US market They may have used the IEC wiring color code. Black or Brown is positive + and Blue is negative - under the IEC code
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Old 07-23-2012, 01:50 PM   #4
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Just Google "dometic (model number) manual" and there is a 99% chance you will get the installation and operating manual on the first page of hits.
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Old 07-23-2012, 06:19 PM   #5
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Figured out it's an RM211 and subsequently found the manual on the Dometic site. BTW - I read that polarity is not important on the 12 volt DC side.

The seller of the fridge said he tested it in all three modes and all worked. I decided to retest the propane mode before installing it and determined it's not cooling. Hummmmm??

Using the manual and a crash course in refrigeration, I am trying to diagnose the problem. Pilot lights fine and stays lit but that's where it all stops - no cooling.

The manual mentions an insulated fuse (10 amp) in the control box. I don't see anything that looks like a fuse. Is this a basic inline fuse holder or something else tucked away?

If any of you folks happen to have a list of things to check/test first, I would love to hear about it. Thanks.
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Old 07-23-2012, 06:44 PM   #6
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See link.

http://gasrefrigeration.net/dom_techdata/MAN_SM.PDF
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Old 07-23-2012, 07:07 PM   #7
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If the flame is ON and there isn't any cooling after an hour you may have a bad cooling circuit. But first,make sure your door seal is very tight when the door is closed and then put a glass of water in the refrigerator and let it run for about an hour and see if there is any temperature drop in the water. BTW: Be sure your unit is level any time you have the gas or electric turned on.
If there is no temp drop after an hour and the freezer compartment isn't cold, it may have leaked down and, although that's not repairable, there are entire replacement cooling sections available.
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Old 07-23-2012, 07:21 PM   #8
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I use one of these contact-less thermometers to check the internal fins for cooling. You should see cooling in the internal fins within minutes. Are you sure it works on 110 volts and / or 12 volts?

Non-Contact Pocket Thermometer
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Old 07-23-2012, 08:00 PM   #9
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Turn it upside down for 24 hours and it may work when you set it up right. But first make sure the chimney above the flame is clear. It's a favorite for spider webs.
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Old 07-23-2012, 09:44 PM   #10
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Thanks for all your replies and great suggestions.

Door seal is good.
Instead of using water inside, I am using my wireless weather station. Placed the remote sensor in the freezer comp. and the main display in the fridge comp. so both temps can be read on the main display.

I'll recheck the 110V operation as I understand it uses the same refrigeration components as the propane mode. If it cools on 110V I assume the refrigerant is up to snuff.

Will let you know. Thanks again.
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Old 07-23-2012, 10:03 PM   #11
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Because there is no air circulation in these refrigerators you may not get an accurate reading measuring air temp. If you leave a good one running empty for 2 days it doesn't really feel cold more than a few inches from the freezer plate. But, if you fill it with food for 2 days it will feel very cold.
BTW: There is no "Refrigerant". It is an ammonia mixture than can't be recharged. If it is only working partially it usually means that the circuit is clogged. If the ammonia charge gets low it means that there is a leak and, in a matter of hours it will vent out. You will smell it.....
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Old 07-23-2012, 10:30 PM   #12
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Quote:
Originally Posted by Bob Miller View Post
Because there is no air circulation in these refrigerators you may not get an accurate reading measuring air temp. If you leave a good one running empty for 2 days it doesn't really feel cold more than a few inches from the freezer plate. But, if you fill it with food for 2 days it will feel very cold.
....
And if you put a small, battery-operated fan inside you will improve the apparent cooling efficiency of the fridge by an astounding amount
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Old 07-23-2012, 10:37 PM   #13
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Yes there is ref

Quote:
Originally Posted by Bob Miller View Post
Because there is no air circulation in these refrigerators you may not get an accurate reading measuring air temp. If you leave a good one running empty for 2 days it doesn't really feel cold more than a few inches from the freezer plate. But, if you fill it with food for 2 days it will feel very cold.
BTW: There is no "Refrigerant". It is an ammonia mixture than can't be recharged. If it is only working partially it usually means that the circuit is clogged. If the ammonia charge gets low it means that there is a leak and, in a matter of hours it will vent out. You will smell it.....
I'm using wikipedia's words rather than my own, mainly because I'm too lazy to make sure I have all the spellings correct.


"A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase transition from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion effects. Other common refrigerants used in various applications are ammonia, sulfur dioxide, and non-halogenated hydrocarbons such as propane. Many refrigerants are important ozone depleting and global warming inducing compounds that are the focus of worldwide regulatory scrutiny."

In the 40s and into the early 50s ammonia was quite commonly used in home refrigerators. I can remember my father draining the ammonia out of our refrigerator so he could fix a leak. Once the leak was fixed the ammonia refrigerant was replaced. This was in the late 40s. The poor dog took a big whiff at the end of hose used to get the ammonia away the house. Poor dog spent considerable time trying to paw the smell out of it nose.
It's still used in many large commercial operations.
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Old 07-23-2012, 11:27 PM   #14
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Currently (no pun intended) the unit is on 110V and after only 15 mins the metal plate in the freezer is getting very cold to the touch. Will put a small container of water in both the fridge and freezer and leave it running the night.

Back to the propane mode, when I turned off the gas valve lever and the pilot flame subsequently went out, about 30 seconds later I heard and felt a "click" in the thermostat. I assume this is the thermal couple changing it's position as it cooled and shut off the gas?? If so, is it safe to say the thermal couple and thermostat is working? I don't hear/feel the same "click" after the pilot is lit unless it makes a quieter sound and I just missed it.

Another question - assuming proper operation in propane mode, when the fridge or freezer calls for cooling is there a burner of sorts that kicks in and then cuts out when extra cooling is completed? Or, is there always a constant flow of gas and flame and constant cooling?
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