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Topic ClosedDead Dometic RM8501
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pgoelz View Drop Down
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Posts: 70 		Direct Link To This Post Topic: Dead Dometic RM8501
    Posted: 07 Aug 2017 at 10:12am
Originally posted by funks

I'm having some of the same problems on my RM8501. On AC the temp will drop down to 38 but switched to gas it goes back up. When on gas freezers working ok but bottom section is still warm. 
The unit looks and fills like its working just fine on gas but something is wrong. 
I cleaned the gas orifice and burner that did not even look dirty and still no improvement. Good flame and heat but no bottom cooling. I order a new gas orifice and a thermistor for the bottom fine in the frig. Will install next week. I'll let you know how it works. 

That sounds pretty nearly identical to my original problem.... works OK on AC but does not cool at all on gas even though the flame is lit.  

In my case, the orifice did not look dirty either but after I cleaned it (alcohol and an ultrasonic cleaner), it seems to perform like new.  See above.  

Note that if the flame is lit, the problem is NOT the thermistor.  If the thermistor is shorted, the unit would not call for cooling and the flame would not be lit.  If the thermistor is open, the unit would call for continuous cool.  If it cools OK on AC power, flame but NO cooling would indicate the flame is either too low or something is blocking the flue.  

A very unscientific measurement.... at least on mine, the flame was silent before I cleaned the orifice.  After I cleaned it, I can hear a very subtle roar when the flame is on with the cover removed and I can hear it gently "pop" when it lights standing next to the fridge inside the (quiet) trailer.  

Paul
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Posts: 70 		Direct Link To This Post Posted: 07 Aug 2017 at 9:58am
Originally posted by pgoelz

It has been on gas for 30 minutes now and the fridge IS starting to cool down.  The freezer fins are very cold but not frosting yet.  The lower fins are also cold..... when it was refusing to cool, the lower fins never went below ambient.  We'll see how it is after three or four hours..... on AC, it was able to reach 36 degrees in that time span.  

So I am cautiously optimistic.  

UPDATE:  After cleaning, it has been on gas for a little under two hours now and A) the freezer fins are frosted over their entire width, B) the lower fins are cold and C) the fridge interior is already down to 39 degrees (outside ambient is 71 degrees).  That is way WAY better than before I cleaned it and I am assuming is fairly nominal performance.  I am VERY relieved to put it mildly ;)  

Paul

ADDENDUM: 

After 2.5 hours on gas at one step below the max cooling setting, the interior is down to 34 degrees at an external ambient of 72 degrees.  I changed it to the middle setting and we'll see where it settles.  This would appear to be entirely nominal operation, and all I did was clean the gas orifice.  The trailer is three years old and we are the second owner.  I suspect the gas orifice was never cleaned since new.  Problem solved and lesson learned.  I am still stunned that there are no leveling warnings anywhere in the documentation, but at least our fix was simple and we didn't kill the cooling unit.  
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funks View Drop Down
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Posts: 98 		Direct Link To This Post Posted: 07 Aug 2017 at 8:57am
I'm having some of the same problems on my RM8501. On AC the temp will drop down to 38 but switched to gas it goes back up. When on gas freezers working ok but bottom section is still warm. 
The unit looks and fills like its working just fine on gas but something is wrong. 
I cleaned the gas orifice and burner that did not even look dirty and still no improvement. Good flame and heat but no bottom cooling. I order a new gas orifice and a thermistor for the bottom fine in the frig. Will install next week. I'll let you know how it works. 
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Posts: 70 		Direct Link To This Post Posted: 07 Aug 2017 at 8:57am
The ride home did NOT fix the fridge.  When we got home it cooled fine on AC shore power but still would not cool at all on propane.  

I just finished cleaning the burner, orifice and flue this morning.  Nothing looked plugged but the orifice is so small that it is difficult to judge if it is partially clogged without a microscope.  My 10X jeweler's loupe was not enough.  After cleaning and re-assembly, the first difference I noticed is that I now can hear the flame "pop" from inside the trailer when it lights.... I used to be able to hear that but not recently.  I can also hear a very slight roar from the flame... don't think I could hear that before I cleaned it but I was not paying close attention to the sound.  My guess is that the flame is now larger than when it was not cooling.  

It has been on gas for 30 minutes now and the fridge IS starting to cool down.  The freezer fins are very cold but not frosting yet.  The lower fins are also cold..... when it was refusing to cool, the lower fins never went below ambient.  We'll see how it is after three or four hours..... on AC, it was able to reach 36 degrees in that time span.  

So I am cautiously optimistic.  

I found the service manual online.  I can't believe it, but Dometic species that the burner should be cleaned at least once a year but they don't bother to tell you HOW.  And this is the SERVICE MANUAL.  Like the lack of any leveling warnings, they seem to assume everyone has ESP.  Yes, it is pretty obvious how to clean it when you take it apart.  But there at least should be a warning about not poking the ruby crystal ;)  

Paul
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Posts: 281 		Direct Link To This Post Posted: 07 Aug 2017 at 7:03am
Years ago, I had a kerosene fridge that occasionally stopped cooling.  Flame was OK, heat coming out of the chimney, etc.  I found that turning the fridge on its side, the side where the riser tube was, it would cool again when set upright and the burner lit.  I theorize that somehow the cooling system developed a gas lock which prevented the circulation of the refrigerant.  It will be interesting if the ride home "fixes" your fridge.  Are there lots of hills and maybe bumpy roads?
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Posts: 70 		Direct Link To This Post Posted: 07 Aug 2017 at 6:21am
No, I'm not lighting with a match.  I'm just looking through the hole to see if the flame looks OK.  The flame lights fine automatically, satisfies the flame sensor and there is heat coming out the top of the flue.  But I can't see enough of the flame through the hole to see how big it is or what color it is from bottom to top.  

This is starting to make some sense.  Two trips ago we ran out of propane way before I thought we should.  I put it down to simply mis-judging the amount of propane we had remaining.  But now I am guessing the cooling on propane was getting worse and worse and the flame ended up on 100% of the time.  

Propane pressure to the fridge seems OK.... the stove burner has a normal size flame and does not change size when I light the second burner.  My guess is that the fridge burner orifice is clogged or there is something in the flame tube.  Our (smaller) fridge in our pop up ran fine for 15 years without any burner maintenance so I kinda overlooked the burner maintenance mentioned (but NOT described) in the RM8501 manual.  

Can't wait to tear into it and see if it is as simple as a clogged orifice.  I have a small ultrasonic cleaner that should work great with a bit of alcohol to clean it out.  I am of course VERY relieved that the cooling unit itself appears to be perfectly OK!  

Live and learn.... I thought that if the flame was lit and the flue exhaust was hot, all was OK.  Perhaps not.....  And now that I think about it, when all was well I remember hearing the flame kind of "pop" when it lit.  I could hear it inside the trailer if it was very quiet.  Now I don't hear that.... the sparker stops sparking when the flame lights but I don't actually hear it light.  Another indication of a clogged orifice or low pressure I think.   

Stay tuned.  I'll report back after I have a close look at the burner later this morning.  

Paul
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Tars Tarkas View Drop Down
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Posts: 1446 		Direct Link To This Post Posted: 07 Aug 2017 at 5:54am
You aren't lighting the flame with match are you??  If you are, that's an important clue.

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Posts: 70 		Direct Link To This Post Posted: 07 Aug 2017 at 5:23am
Originally posted by pgoelz

If it cannot cool on gas, I'll have a closer look..... while on gas, the flame DOES light, the controller sees the flame and does not sound any alarm and the exhaust out the top of the flue is very hot.  But I have not checked for internal flue obstructions or actual flame size.  I'm also wondering if perhaps the flue and the boiler tube have become separated so there is not sufficient thermal transfer?  I don't know how it is built.... if the cooling unit is replaceable, they can't be welded.  Perhaps they have just lost mechanical connection?  Or perhaps the flue is actually part of the boiler?  

Paul

The fridge was at 36 degrees after running four hours on AC shore power in the driveway.  I figure that is pretty normal.  So before we went to bed I switched to gas.  This morning the interior is at 50 degrees and rising, same as when we were camping.  So it is definite.  The cooling unit is fine..... we just have a much simpler (and less expensive) issue with the flame or flue.  The flame is on and satisfying the flame sensor but beyond that I could not see enough of it through the match light hole to see how big or blue it is.  Today I'll dig into it and see what the real issue is.  

Paul
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Posts: 70 		Direct Link To This Post Posted: 06 Aug 2017 at 8:37pm
OK, original poster here and I'm back home after a week camping with my dead RM8501.  Good thing we use a Coleman cooler for misc. camping stuff...... emptied it and filled it with ice and we at least didn't lose any food.  

1.  I measured the slope on the driveway... this is the maximum out of level I have ever subjected the fridge to.  It measures 2.1 degrees fore / aft and 0.8 degrees side to side.  That is well within the 3 degree / six degree spec I got from Dometic when I pressed them.  So I didn't kill it like I thought I might have.  However, the first owner might have.  In either case, without any warning from either Dometic or Forest River, how should either of us have known?  

2.  I tried re-starting it several times perfectly level and on gas while we were camping this week.  Each time, the left side of the freezer fins got cool enough to condense but the right side and the entire lower fins were still at ambient even after several hours.  Definitely not normal.  

3.  When we returned home, I un-hitched, leveled the trailer and started the fridge on AC shore power.  To my amazement, it is cooling normally.  The freezer fins are frosting up and the internal temperature is 43 degrees (and I assume still dropping) three hours later.  Tomorrow I'll switch to gas and see if it can hold temperature.  Maybe the sloshing of the 500 mile trip home while powered off "burped" something?  

4.  If it cannot cool on gas, I'll have a closer look..... while on gas, the flame DOES light, the controller sees the flame and does not sound any alarm and the exhaust out the top of the flue is very hot.  But I have not checked for internal flue obstructions or actual flame size.  I'm also wondering if perhaps the flue and the boiler tube have become separated so there is not sufficient thermal transfer?  I don't know how it is built.... if the cooling unit is replaceable, they can't be welded.  Perhaps they have just lost mechanical connection?  Or perhaps the flue is actually part of the boiler?  

Paul
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Posts: 159 		Direct Link To This Post Posted: 04 Aug 2017 at 11:23am
Originally posted by funks

I think I'm having the same problem with our three year old RM 8501 cooling on gas. It runs on AC and DC just fine. Is yours running on AC and DC?  I'm trying to nail down the problem and If I do I'll let you know.  I also have a good blue flame and the tower is really heating up but it just won't cool down. 
Good Luck and keep posting

Not sure who you are talking to without quoting the original poster, but I've been on here for a week or so complaining about my brand new 2018 R-pod not cooling as well on gas as on either of the electrics, when in reality, in over 40 years of Rving and a dozen or so single-door Dometics, gas has always, traditionally, been the most efficient.  Right now mine is running 5-7 degrees warmer on gas than either 12 volt or 120 volt.  And believe it or not, my 12 volt is the most efficient by about 2 degrees.  Mine has been at the dealer all week while they try to find out why and I'll post their results on here when I get word.  I don't expect they'll find anything because my propane flame is also blue and the boiler is very hot.
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