Testing a used Dometic fridge

[pamelake]

I am replacing my original Dometic fridge in my 74 Tradewind with a used Dometic fridge of undetermined age. I was told by the seller that it works, but want to test it before installing. Here is the deal. The new one requires a DC plug in. My trailer is currently without batteries. This is my plan. Please someone tell me if this make sense. There are two wires coming out of the back of the fridge that require DC. I will wire a cigarette lighter plug in to these wires. Then I plug the cigarette lighter into a to a DC to AC converter and plug this into AC. Then I plug in the regular AC and turn the fridge on. Am I thinking this through correctly? Thanks, Pam (a nurse, not an electrician)

[flyfshr]

Pam,
Undoubtedly, your fridge is not meant to operate on 12 voly only. If yours is like mine, the 12 volt is needed for the panel switches to work properly while running on propane. It will fry your 12 battery in short order if that is all its hooked up to. Some of the fridges will operate on 12 volt only through the umbilical cord while the vehicle engine is running but without the alternator providing the juice will drain a car battery in just a few hous. Is your fridge a three way i.e.: 110 volt, 12 volt or propane?

FF

[pamelake]

No, the fridge runs on 110 or propane. My understanding is that the 12 volt is to run the panel. The repairman I talked with at Camping World said having the 12 volt plugged in is necessary even when running on 110 volt. Do you think that is correct? Otherwise I could just plug the fridge into my 110. If I need the 12volt to run the panel while running on 110, do you think my plan will work? Or will I fry something??? Other then my brain on 'electrical story problems'.....

Originally Posted by flyfshr

Pam,
Undoubtedly, your fridge is not meant to operate on 12 voly only. If yours is like mine, the 12 volt is needed for the panel switches to work properly while running on propane. It will fry your 12 battery in short order if that is all its hooked up to. Some of the fridges will operate on 12 volt only through the umbilical cord while the vehicle engine is running but without the alternator providing the juice will drain a car battery in just a few hous. Is your fridge a three way i.e.: 110 volt, 12 volt or propane?

FF

[stephen.s1]

Methinks the repairman is 100% correct. When you fire it up, run it on AC, then unplug the AC and be sure it switches to, and works on gas.

GL and best for '05

[Mike76251]

If you don't have the switch panel on yours (mine has no such panel) and you try to run it through that inverter.......you will no doubt fry the inverter as these fridges pull MANY amps when running on 12v.
Also, remember the old trick of turning the fridge over on it's top if it will not cool.
If they sit too long unused, the liquid inside the lines will form a solid mass in the bottom and agitation is sometimes neccesary to get it back into a liquid state.

[jimmickle]

The current Dometic gas/electric run on either 110v AC or propane. Their controls require 12v DC to operate. No 12v=No operation. The current draw is very low, or we wouldn't be able to boondock as our batteries would quickly discharge. My only concern with using the inverter is the voltage and quality of the DC. Circuit boards are expensive, so I would want to be sure that the DC is clean. Could you plug it into your car cigarette lighter? Or borrow a battery somewhere?
Good luck on your tests.

[Hit'nMiss]

Well I am now more confused than when I first read this thread.
The "old trick" of turning the fridge upside down is a new revalation as far as I can tell. or is it just an April fool stunt?
What is the liquid that becomes solid? And what would upside down have to do with turning a solid (back) into liquid?
I would like to be directed to more about it. Is there another thread where it is discussed?

As for you Pam I would wait for more definative advice because the one thing I do totally agree with is the cost of circuit boards being rediculously high.
Might have been helpful if you'd posted the model numbers.
Fridges are one of the most necessary but expensive items in these old trailers. Much more expensive than ACs and apparently less reliable.

I used to think I knew which members were to be most "trusted" with electrical advice, but I have found that it is the subject most misunderstood and most over advised not to mention most inaccurately advised on this and other Airstream forums. Be careful.
Oh I know very little about electrical too so your'e not alone.
Good luck.

[thenewkid64]

I would just hook the fridge to a known good 12 VDC source, Like an RV Battery.....


As for the turning the refer upside down this is what I have been told.

Running a fridge out of level can cause the coolant to actual boil dry and create a a plug in the lines where the coolant is supposed to flow back to the boiler. This plug will cause a refer to stop working. Turning the refer upside down (do not run the refer upside down) causes the liquid to soak the plug so it will unblock the pipe.

There is also a situation where a refer will get blocked by what is described as a bubble. This is a coolant blockage as well. Turning the refer over can clear it. This is also referred to as burping the fridge.

If the fridge is working there is no need to do either. Sometimes these things work, but they are the last chance in many cases before writing a sizable check for a new refer. If you attempt either "fix" do not have the refer connected to power or gas, and it needs to be left upside down for a few days.

[Mike76251]

I was just assuming that the fridge was pretty old and might not have a control panel.
If it was old enough not to have one and she hooked it up through a invertor........might blow a good invertor.
Those things can be rather high.

Also......sorry for making the burping fridge procedure sound like a joke. I didn't give out enough details I guess. I didn't because I thought it was pretty common knowledge.

[Condoluminum]

Pam;

Assuming you've found way to furnish 12V power to fridge control circuit and propane source, or else 110V source (or both..) ther eis one more bit of advice.. Barring either leaks from back of tubing (smelly and messy and noticeable) other two failure modes are blockage of tubing (internal) which will appear as failure to get cold OR.. failing "Control Board", which causes fridge to start up and get cold, but then shut down after 6 to 12 hours... This is due to Dometic practice of embedding older boards in plastic compund that lets heat build up.. This heat will cause component failure and board shutdown when it gets hot.. Cure is either Dometic or Brand X replacement control board ($120 or so..) before buying new refrigerator at $800+... I think Dinosaur is the leading independent maker of contol boards for Dometics... (Beware that a number of dealers would rather sell new refrigerator and install it than troubleshoot and repair board in existing units..) Less risk of recurring problems, and more margin for shops...

John McG

[gsymes]

Not having done it myself, just go by what I have read. Burping does work about 50% of the time. Threads on this site lead me to the sites that verify this. There is a powder in the ammonia cocktail that run these units, sometimes in a off level condition the powder clogs up. Most units that ran 3 way 110v, propane,and 12v need a lot of 12v amperage to run effieciently.
http://www.gasrefrigeration.net/how_they_work.htm
This site offers great information on the refer.

[Mike76251]

Yeah...... burping does not work every time but I would sure try it before I laid down $800 or so for a new one.
I hope I never have to replace my '72 fridge because I do not want any electronics to replace every few years.
I still don't know why they went with electronics on the newer fridges because the only thing to go bad in a fridge like mine is mis-use (off level running), or rust-out.

The rust is going to get mine one of these days because the sodium pipes are not stainless..........drats.

My neighbor has a sodium fridge (old hospital type) that has been cooling constant for 40+ years and still going strong.

Gotta hand it to Albert Einstein..........he got that idea right.