Fridge flame failure device stays open

[ronbazin]

This is my first post on this excellent website.

I have a 1988 Starcraft.  I've had issues with the fridge (Dometic model RM190) ever since I bought the trailer several years ago.  It seems that the burner flame goes out sometime after it is initially lit (from a few hours to a day after lighting the flame).  The fridge does work, as I've recently been able to freeze water in a cup placed in the fridge.  Thanks to this forum, I've built myself a manometer and checked the gas pressure to the fridge.  It was at 10" and I increased it to 11".  Thanks to the manometer I've also been able to gain some insight into another potential problem that might relate to the flame going out over time.

Initially when I first light the flame, it is difficult to keep it lit, as it just flares up and then goes out.  After 2-4 times of doing this the flame stays lit.  Now the interesting part.  After the flame has been burning for a short bit, I turn it off by closing the gas valve.  When the flame is gone, I open the gas valve again, and I get gas pressure back in the manometer, without depressing the plunger on the flame failure device.  I can actually relight the flame without depressing the plunger on the flame failure device.  After about 30-35 seconds there is an audible click, which is the flame failure device closing (as the water column on the manometer drops).  Is this normal, or is there an issue with the flame failure device, or even possible the thermocouple which activates this device?  Is it a matter of cleaning out the flame failure device?  And could this have anything to do with the flame going out over time?

Any help would be much appreciated.

Ron

[austinado16]

Your fridge is working normally....except for the flame randomly going out, which I addressed in your other thread.

The reason you can relight the flame immediately after extinguishing it, is because the thermocouple is still hot, and therefor, still supplying voltage to the magnetic solenoid in the safety valve (what you are calling the flame failure device).  So with voltage still present in the magnetic windings of the solenoid, the solenoid continues to hold the pin up insided the valve.  As the tip of the thermocouple cools, the voltage drops off, and the magnetic windings stop being a magnet......dropping the pin into the gas valve's oriface with that click you hear.

Glad you were able to follow my instructions and build a manometer.  I found that online, so I can't take any credit for the idea.  I just built one, and thought if I posted it here, other's might find it useful.

My best advice with your fridge is to remove it from the camper.  Takes about 15min.

Then take the burner box off, remove the burner tube (what the flame comes directly out of) and then take off the paper covered air supply tube, the metal cross-over tube at the top, and then down inside the chimney (above the flame) you'll find a twisted metal baffle hanging by a wire.  Pull this all out, clean it all, clean inside the chimney, use rubbing alcohol to clean the gas oriface that's inside that brass fitting upstream of the burner tube........etc.  Do the whole works.  Even pop the fittings off both sides of the t-stat and blow through it backwards.  You'll find a little round paper/gauge type filter upstream of the t-stat.  You might check to see if you can blow through it easily with your mouth.  Or, leave it out and try the fridge without it.

Probably if you clean all this up, you'll have a working fridge.

When chasing my "flame goes out" on my own 1987 Dometic, I found that my burner tube was supposed to have something like 4 slats cut into it where the flame sits.  On mine, all my slats had rotted off, fallen out, and left a big rectangular opening!  It looked "normal" until I got a second fridge for parts and saw it's burner tube with the slats still in tact.  Installing a good burner tube cured my problem.

[ronbazin]

Wow, thanks austinado16 for your information from both threads (see also Dometic thermostat problem).  You are a wealth of information.  And by the way, I really enjoyed building the manometer.  So simple yet so effective, as it allowed me to eliminate low (or high) pressure as a possible problem with my fridge.

So I guess I

[austinado16]

I have to give credit to everyone here who helped me when I showed up out of the blue in Feb'07.  I didn't know anything about any of this stuff, but I'm a big DIYer, an automobile mechanic, and I love to restore stuff.....so it's been a learn-by-doing sort of process.

My fridge started off this second season with the flame going out frequently for no apparent reason.  I was messing around with the burner box area, doing a manometer test, etc. and I smacked the gas pipe with a small combination wrench, just where the pipe goes into that burner box.  As I did, my flame dimmed a little.  I smacked it again, saw a bunch of small sparks in the burner box, like carbon being knocked loose, burning up and flying away....and the flame got really bad.  So I reasoned that my burner tube and my oriface were probably sooty inside.  I blew through both with compressed air and that made a big difference and curred my problem.

I think a dry brush inside the chimney would be fine.  You can probably find a bottle brush that size.  I don't think I'd get it soap or wet, or use a solvent on it.

I would disconnect both sides of the t-stat and blow through it in both directions, maybe with just your mouth, and/or a can of air like you'd use on a computer key board. Not sure I'd put compressed air up to it from an air compressor and blow gun.  But close the t-stat down to "0" and blow both ways, and then do it again with it at "9" or "Max".  That way hopefully you'll be blowing through the tiny "off" oriface in there.

Remember when you're loosening or tightening fittings on piping, use your wrenches against each other, so that you aren't loading the piping. You don't want to bend, twist, or break the piping or the valve(s), etc.  When you reattach the fittings, attach them all just partially finger threaded on.  This allows you to wiggle the pipe assemblies as you are getting individual flare nuts started, and keeps you from being OH SO SCREWED by cross threading or stripping out something.  Assemble it all loose, and then tighten it all up......again, using the wrenches against each other so you aren't loading anything weird.  Check for propane leaks afterward with a wipe of soapy water looking for bubbles.  I'm lazy and I just run my butane BBQ lighter over the assembly and look for flame.  If I find a flame, it's easily blown out and the fitting tightened.......but I'm not recommending this!

[ronbazin]

Well I managed to get my fridge out yesterday.  It took a long time because the hole that had been cut to place the fridge in was so tight that it simply wouldn't come out.  I finally had to break part of the paneling above the fridge to loosen it up.  It easily came out after that.

I took it apart today and cleaned everything out with pressured air, a brush and alcohol.  All in all it wasn't that dirty with soot, considering it's 20 years old.  The gas line seemed OK as well, but it's hard to tell if there might have been microscopic pieces of soot affecting the t-stat or the orifice.

I did leave the small filter plug upstream from the t-stat in the gas line.  I may take it out if performance doesn't improve.

I'll be placing the fridge back in the trailer tomorrow and I'll see what it will do.

I'll post later with the results.

[wavery]

Well I managed to get my fridge out yesterday.  It took a long time because the hole that had been cut to place the fridge in was so tight that it simply wouldn't come out.  I finally had to break part of the paneling above the fridge to loosen it up.  It easily came out after that.

I took it apart today and cleaned everything out with pressured air, a brush and alcohol.  All in all it wasn't that dirty with soot, considering it's 20 years old.  The gas line seemed OK as well, but it's hard to tell if there might have been microscopic pieces of soot affecting the t-stat or the orifice.

I did leave the small filter plug upstream from the t-stat in the gas line.  I may take it out if performance doesn't improve.

I'll be placing the fridge back in the trailer tomorrow and I'll see what it will do.

I'll post later with the results.

If I went to all that trouble, I think that I would change that thermocouple. They aren't that expensive. It's easy to change and usually the first thing to fail on the fridge.

[ronbazin]

Possibly a good idea to change the thermocouple.  Now having taken my fridge apart, however, I realize that the whole process is not that complicated.  Indeed the thermocouple could probably be changed without even taking the fridge out, however it is easier to work with the fridge on a benchtop rather than still in the trailer.

Any idea where I could get a thermocouple for a 1988 RM190 Dometic fridge?  Will any generic thermocouple do?


What I want to report here are my results from the work I did.  I fired up my fridge on Sunday at about noon.  The flame lit immediately and stayed lit right from the get go.  Previously it required about 3 attempts before staying lit.  The flame was perfect, and by early evening it was 9 C in the fridge at setting 5.  I dialed the t-stat to 7 and it was 2 C by bedtime (the nights are cooler here already at this time of year, hence the more rapid cooling).  The fridge stayed at about 0 C all night.  In the morning I dialed the t-stat to 6 and by late morning, it was 6 C in the fridge, despite the fact that the inside trailer temp was at least 25 C.  The flame stayed lit the whole time, diminishing in size when the required fridge temp had been reached as it should.  So all in all a success.

The only slightly disconcerting aspect was that by early evening the fridge temp has increase to 12 C, but this was at setting 6 on the t-stat, so I guess it's just a matter of changing the setting throughout the day to keep the proper temp.  I purchased a wireless temp gauge that gives out an alarm when the measured temperature reaches the freezing mark.  I wish there was something out there that also allowed you to set an alarm for when the temp would go above a selected level (to ensure that it also never gets too hot in the fridge).  Any idea if this type of temp gauge exists?

[austinado16]

Nice job getting it working again.  Yours performs about the same as mine.  Mine is very outside temp sensative, and the hotter the day is outside, the more my fridge inside temp creeps up.  I've installed a boatload of insulation around mine.  Put in a baffle at the recommended location to make sure the air flow up the back of the fridge had no choice but to go over the coils, and even installed a computer cooling fan in the upper louvered opening so that I could move more air through the fridge coils on hot days.  So far, I've only seen a marginal improvement....at best.  Even with the fridge set on "max."

There is a digital fridge thermometer that you stick on the outside of the door, and it has a thin "ribbon wire" type wire that goes inside to a temp sensor.  This will give you fridge temp at all times.  The one I have doesn't have an alarm, and I don't know if they are available that way.  Maybe so?

You'll find the fridge will do better "temp reading wise" if you have food in it.  The food stays cold and stores cold.  I learned that on here while doing a week long fridge test on my fridge.

Sounds like your thermocouple is just fine.  Your flame problem before was from poor flame performance and/or air flow in the burner box and chimney. They're really sensative to that.  If you had a bad thermocouple, it wouldn't make voltage once hot, and so you wouldn't be able to keep the flame lit.

[ronbazin]

Well thanks greatly for all the help.  My fridge has similar additions (insulation on the outside, baffle near the coils etc.).  I guess it's just a function of these fridges.  I might try a fan on the outside, and possibly one on the inside, as I recently saw in an RV parts catalogue.

Now I just have to wait impatiently until next spring to start camping and use the fridge again, after so many years of not using it.