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pgoelz 
Groupie 
Joined: 22 Jul 2016 Online Status: Offline Posts: 70 |
 Topic: Dead Dometic RM8501Posted: 07 Aug 2017 at 6:21am |
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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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sailor323
Senior Member 
Joined: 11 Jun 2015 Location: S Central KY Online Status: Offline Posts: 281 |
Posted: 07 Aug 2017 at 7:03am |
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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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pgoelz
Groupie
Joined: 22 Jul 2016 Online Status: Offline Posts: 70 |
Posted: 07 Aug 2017 at 8:57am |
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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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funks
Groupie
Joined: 05 Nov 2014 Location: CALIF Online Status: Offline Posts: 98 |
Posted: 07 Aug 2017 at 8:57am |
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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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pgoelz
Groupie
Joined: 22 Jul 2016 Online Status: Offline Posts: 70 |
Posted: 07 Aug 2017 at 9:58am |
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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pgoelz
Groupie
Joined: 22 Jul 2016 Online Status: Offline Posts: 70 |
Posted: 07 Aug 2017 at 10:12am |
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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Wood River Pod
Senior Member
Joined: 30 Sep 2016 Location: Wood River, ID Online Status: Offline Posts: 153 |
Posted: 07 Aug 2017 at 11:31am |
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Paul,
Great to hear that you figured it out and it's working. Way to stick with it! Based on your comment that the Dometic service manual does not do a good job (or no job) of explaining the annual cleaning procedure, would you be willing to please put together a quick run down of what the steps are to clean the burner, orifice and/or other. I personally have no knowledge to take that project on, but I can follow directions very well. I'd even help you to include some pictures along with the steps. Based on all of the comments from your post, I think the community would greatly appreciate the info, and it will be an education for me. I don't think I've seen a post that details the cleaning process in detail. There are a few YouTube videos, but none specifically for the pod model fridge. Send me a PM if you are interested. I think pictures would be most helpful. Thanks Jeff
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fwunder
Senior Member
Joined: 04 Oct 2013 Location: New Jersey Online Status: Offline Posts: 1676 |
Posted: 07 Aug 2017 at 12:13pm |
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This was my experience about a year ago. Model RM8501. Perhaps the pics might help:
This past weekend, the problem reappeared. Cooled fine on AC, but not on propane. My best guess is that somewhere along the road I got some dirty LP and this is the reason I have had to repeat this procedure several times. Easy to do, but a filter would be better. This AM, I repeated the cleaning above. It's cooling fine now on LP (after about two hours running). This time I am measuring boiler temp with infrared thermo @ top of boiler mantle. Perhaps I can use this temp as a diagnostic tool in the future. Seems to be holding steady @ 280-284.  fred
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2014 RPod 178 => MyMods and Buying Habits
2008 4Runner Limited 4.0-liter V6 Yes, those are wild ponies dining on grass while dumping tanks! |
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spydie
Senior Member
Joined: 25 Jul 2017 Location: New Mexico Online Status: Offline Posts: 159 |
Posted: 07 Aug 2017 at 12:21pm |
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I just made a trip to my local RV dealer to see how they are progressing after a week with my new 2018 Rpod refer (which cools fine on AC and DC but runs 5-7 degrees higher on LP). They were able to duplicate my complaint while the Dometic was in the Rpod. But Dometic told them they had to take it out of the Rpod to run the tests, so when they put it in the shop, it's working fine, about 34 degrees only turned up about half way on the temp controller. He said that today he's going to call Dometic back and discuss the mounting in the Rpod. He said the sides were hot when he took it out and that indicates the insulation is packed too tight. He's going to discuss all the mounting problems with them and see if there is some way to increase efficiency. I'll let them have it another week and see if it does any good for me.
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2018 R-pod 176
2017 RAM 1500 5.7L Hemi 
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pgoelz
Groupie
Joined: 22 Jul 2016 Online Status: Offline Posts: 70 |
Posted: 07 Aug 2017 at 12:26pm |
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Let me see if I can run through the cleaning steps I used here..... this refers to the RM8501L. And of course, turn the gas and the refrigerator off before you start ;)
1. Remove the screw securing the sheet metal burner cover. 2. Use a 7/16" open end wrench to un-screw the gas pipe nut where it enters the VALVE assembly (NOT the burner). I found that it is safer to remove the burner and pipe as one and disconnect the pipe from the burner in a controlled environment since the orifice is a little piece that fits into the burner and can easily fall out if you remove the pipe from the burner in the fridge recess. 3. Remove the screw securing the burner to the flue and then remove the pipe from the valve. 4. At this point, the igniter and flame sensor are still attached to the burner. Remove the screw securing the igniter bracket and the burner and pipe can now be removed from the fridge enclosure. 5. In a controlled environment (ie., where you can find stuff you drop), disconnect the pipe from the burner block and carefully remove the orifice. The orifice is basically a cupped washer with a tiny hole. The hole is actually a ruby with a hole in it so that it does not erode from the gas passing through it. 6. I used alcohol in an ultrasonic cleaner to clean my orifice. Not sure if you can just soak it and swish it around in a dish and get the same results. I am also not sure what is actually the best solvent to use. I have seen alcohol, carburetor cleaner and soap and water mentioned, but I don't know what we are trying to dissolve.... dust and dirt, or something gummy from the gas? There are plenty of warnings online to NOT use any sort of implement to poke through the orifice, since you can damage the opening. 7. Blow out the pipe with compressed air and also inspect the burner block to make sure nothing has made a home in there..... the burner block is where the gas jet mixes with air and then flows upwards where it ignites. There is plenty of room in there for spiders and critters. 8. Remove screw securing the "T" cap from the top of the flue and remove the cap. Remove the baffle that is suspended in the flue on a bent wire. Pass a small bottle brush through the flue to make sure it is clean and un obstructed. In my case I didn't have a bottle brush so I used a wadded up piece of paper towel and pushed it down with a plastic pushrod. BAD MOVE..... it got stuck half way down and I thought I was in serious trouble for a while. Not sure if there is structure in there or what, but I finally got it to pass all the way through and since it came out intact I figured all was well. Finish off by blowing some compressed air down the flue if you can. 9. Re-assemble and test. My best guess is that stuff sticks to the edges of the orifice and slowly closes it off, gradually reducing the size of the flame. Cleaning restores full flame. I am trying to figure out how to gauge the cooling efficiency. Since there is no indication of when the flame is on and no way to determine what the stabilized duty cycle is, I can't figure out how to tell if I am completely back to normal. But it SEEMS to be normal. Paul
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Dead Dometic RM8501