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NanMWright

Dometic Fridge 50 deg. on propane

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Hi Folks - I have a Dometic refrigerator (Model RM2652) in my 2007 Class C FR Sunseeker.  If I'm on shore power, it seems to cool perfectly, well below the 40-42 degrees I want.  However, I boondock for weeks at a time and the fridge on propane can't seem to get cooler than 50 degrees.  The freezer stays extremely cold and frozen food is fine. But normal fridge foods - milk, yogurt, meats - only last 7 days at the most.

I cleaned the air flow tube, verified that the igniter works, and the unit is getting adequate propane. I've taken it off the auto electric/propane option and set it to only use propane. (It tried to run the fridge on electric whenever I turned my inverter on...sending the coach batteries into a downward spiral.)

This Dometic has 'automatic, factory specified' temp control, so I don't have the option to turn it down. 

Is there anything else I can try...  Thanks, Nan

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My follow-up to this post is that I found the thermister was set all the way to the coldest setting, or at least was sitting at the upper-most point on the fridge fin. Still, the fridge is not cold enough to keep food.  I wonder if the termister is not working, since I can't see any other dials or tabs that would allow me to lower the temperature.   Nan

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OK, if it cools properly on 120 VAC but not on propane-- then the cooling unit is probably OK.

You say you cleaned the burner tube-- did you remove it to clean or just blow it out?  Were the vertical slits still in good shape or rusty?

Have you checked gas pressure-- low PSI (11 column inches of water is spec) will cause smaller than normal flame and therefore less cooling?  Propane regulators are cheap-- around $25 and not unusual to be bad after 11 years.

Do you have an auxiliary fan behind the refrigerator (in the outside area)?  If so, and it is running, it will move more air when on shore power (battery voltage higher) than when dry camping.

Verify that you have the correct (very minimal) clearance between the coils and outside wall-- specs are in your refrigerator owners manual.

Lastly, if that side of the coach is in the sun,  cooling unit will not perform as well.

ALL these factors are cumulative.  It is often small degradations of several factors that cause loss of cooling performance rather than one big one (assuming the cooling unit is OK).

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Hi Nan, I don't think  the thermistor is at fault if it works fine on shore power. When boondocking are you level? Being level is a must for proper operation of fridge. Most campground sites are fairly level, witch may explain why it seems to work on shore power. Put a small level on shelf's of fridge in both directions to see where you are at. If you still suspect thermistor problem, unplug thermistor at control board, this puts fridge in maximum cooling mode. If it cools down unplugged, then replace thermistor. Hope this helps.

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Nan, Brett and Frank have covered things to check and I can not add anything other then to check the battery voltage, Brett touched on it. The closer you are to 12.5 volts the better. So could you post the age of the house batteries. 

Do you use Solar to supplement you 12 volt requirement?  

Rich.

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Thanks Folks,

I'm working through your suggestions and I see that the cumulative small problems may be the culprit.

I am running the RV off of an external propane cylinder and I don't have the ability to test the gas pressure from the cylinder. But I put it back on the house propane tank (which should be the default pressure) and the flame burned higher and hotter visually.

I am not totally level...canted to port so that the fridge is facing slightly (not excessively) downward. Front to back are in spec.  I can attempt better leveling. 

I use solar but I haven't been keeping the batteries (brand new) above 12.5.  I keep them above 12V but you indicated that the fridge needs 12.5, so I can shut down my inverter earlier in the day and keep the batteries at 13V when I go to bed. That way the voltage should not drop below 12.5 during the night. 

I have some ice build-up in the freezer so thawing might help.  I'll do that when I have someplace to put the food.

I'll test the thermistor after I've worked through the simpler corrections. 

Thanks so much for the suggestions.....This really helped.   Nancy

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Absolutely, if flame is too small due to low propane pressure, it will not cool properly.

And defrosting is important-- ice is a great insulator,  limiting heat transfer.

See if anyone around you has an ice chest you can borrow for an hour.  If not, even a cardboard box will work.

Turn off the refrigerator.  Wait one hour. 

Remove everything from the freezer and put in an ice chest or cardboard box.  If box, cover with towel or something to minimize defrosting.

Remove things from the refrigerator section top shelf so you can access the cooling fins.

Open both freezer and refrigerator doors.

Use a hair dryer on low heat, NOT sticking the front inside the refrigerator-- you don't want to warp the plastic.

Defrosting should not take more than 10 minutes.

Close doors and turn on refrigerator.

Return stuff after it has been running for 20-30 minutes.

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Nan, The control boards will run at 11.00 volts, The reason the 12.5 was mentioned is in regards the to fans that move air behind the refrigerator - if your coach has then install. Those fans move more air over the coils at the back and more air movement equals better cooling.

The fact that you can see a difference in the flame with the spare tank on line - will also help keep things cooler. 

The one item I forgot to mention was, what we call the dollar bill test.    Place the bill between the door edge and the refrigerator box at multiple locations - pull on the bill and if it slides out easily - the seal has air space at that point - that allows the cool air to seep out. Raising inside the temperature.

Rich.

Nan, Brett mentioned defrosting the frig. and while that is going on, we clean the door seal area top, sides and bottom.

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Another fine-tuning point-- make sure the "restrictor" is in the end of the  refrigerator condensate drain, OR form a drip loop so that warm humid air can not flow up the drain hose into the refrigerator.

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1 hour ago, NanMWright said:

Thanks Folks,

I'm working through your suggestions and I see that the cumulative small problems may be the culprit.

I am running the RV off of an external propane cylinder and I don't have the ability to test the gas pressure from the cylinder. But I put it back on the house propane tank (which should be the default pressure) and the flame burned higher and hotter visually.

I am not totally level...canted to port so that the fridge is facing slightly (not excessively) downward. Front to back are in spec.  I can attempt better leveling. 

I use solar but I haven't been keeping the batteries (brand new) above 12.5.  I keep them above 12V but you indicated that the fridge needs 12.5, so I can shut down my inverter earlier in the day and keep the batteries at 13V when I go to bed. That way the voltage should not drop below 12.5 during the night. 

I have some ice build-up in the freezer so thawing might help.  I'll do that when I have someplace to put the food.

I'll test the thermistor after I've worked through the simpler corrections. 

Thanks so much for the suggestions.....This really helped.   Nancy

Do you have a regulator on your external tank? Where does it connect to your propane supply, before or after the regulator on the coach? I think the main issue is low propane preshure off the external tank as you say it works good off the RV tank. If you are plugins in after the regulator on the Rv you might try a new 2 stage regulator. If plugged in before the regulator on the coach you may need to eliminate the regulator  on the external tank because going through 2 regulators may be restricting the flow.

Bill

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19 hours ago, WILDEBILL308 said:

Do you have a regulator on your external tank? Where does it connect to your propane supply, before or after the regulator on the coach? I think the main issue is low propane preshure off the external tank as you say it works good off the RV tank. If you are plugins in after the regulator on the Rv you might try a new 2 stage regulator. If plugged in before the regulator on the coach you may need to eliminate the regulator  on the external tank because going through 2 regulators may be restricting the flow.

Bill

Bill: Attached are a couple pics of my Extend-a-Stay setup.  The cylinder comes in after the valve on my house tank. What kind of regulator do you suggest? One for the cylinder? Something that attaches to the house side?

Rich: I can pass a dollar bill all the way around my door when it's closed and hooked. Ugh.

I defrosted the fridge, then set it to cool again on house propane.  The freezer came on immediately. The fridge stayed at 60 degrees.  I'm running my generator now and the fridge is cooling rapidly.

Nan

extendastay.jpg

extendsetup.jpg

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Nan,

The propane regulator is under the gray/silver plastic cover on the right of the top picture.  So, line pressure to appliances should be the same on coach tank or outside tank-- above you mentioned that flame was higher on coach tank?? Not sure that makes sense unless the auxiliary tank is empty OR you opened the valve on that tank too quickly and it is not allowing full gas flow. Try turning the valve on the auxiliary tank off and back on SLOWLY with all propane appliances OFF.

 

Please confirm from my first post above: " You say you cleaned the burner tube-- did you remove it to clean or just blow it out?  Were the vertical slits still in good shape or rusty? "

 

 

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Looks like the regulator is under the gray cover to the right of all your brass connectors/valves/etc.

However, if the flame burned brighter on the house tank than on the external tank, then perhaps the problem is in the Extend-a-Stay system. Have you checked to be sure there there is nothing causing a blockage in the fittings? Hard to tell from a photo, but the fittings that you've got on the Extend-a-Stay system appear to be smaller than those on your house tank itself, so it wouldn't take much to cause a restriction.

You said that the flame was larger on the house tank...did the fridge cool better when on that tank?

Have you confirmed that the valve on your built-in tank is closed/open according to the instructions in the kit for the external tank?

Any chance that the external tank was turned on its side and liquid propane was allowed to flow through the valve instead of vapor?

Has the fridge cooled on a different external tank in the past? If so, perhaps this tank and/or the tank's valve is defective?

Just throwing these out there for consideration and to help run through some potential problem areas. Not saying that these are necessarily the case.

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17 minutes ago, wolfe10 said:

Nan,

The propane regulator is under the gray/silver plastic cover on the right of the top picture.  So, line pressure to appliances should be the same on coach tank or outside tank-- above you mentioned that flame was higher on coach tank?? Not sure that makes sense unless the auxiliary tank is empty OR you opened the valve on that tank too quickly and it is not allowing full gas flow. Try turning the valve on the auxiliary tank off and back on SLOWLY with all propane appliances OFF.

 

Please confirm from my first post above: " You say you cleaned the burner tube-- did you remove it to clean or just blow it out?  Were the vertical slits still in good shape or rusty? "

Brett: The first thing I originally tried was to open the burner area, remove the tube and completely clean the tube and igniter with an alcohol swab...then re-insert it and confirm that it burned blue and consistent. Vertical slits were in ok condition. Small amount of rust, mainly on the frame of the tube. I never thought about the way I open/close the house or external cylinder.  The flow to my cooking stove (from the external) is strong so I assumed the flow to the fridge would also be strong and consistent. My perception that the fridge burner worked better on the house tank could be totally subjective.  Using the house tank did not improve the fridge cooling.  I'll try the slow-on recommendation...Nan

Richard:  I'm using some of your suggestions to continue troubleshooting.  The external tank works fine for my stove and furnace, so I don't think there is any problem with the tank. I'll work through your other ideas.  Thanks for taking time to help me think through this.  Nan

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Nan,

Most every RV place can check propane pressure in a matter of a few minutes.  If that is not practical (don't know where you are), it may be more practical to just replace the regulator-- around $25.

If you do replace it, verify that the regulator is designed for HORIZONTAL INSTALLATION. The vent (screened part) needs to be perpendicular to the long axis of the regulator.  Said another way, you do not want a regulator designed for vertical installation.  Price is the same, but they are NOT interchangeable.

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Brett -  I'm going to re-examine the burner...make sure nothing is blocking the fuel or flame.  I think I did a good job of cleaning it, but it's easy enough to check and re-do if necessary.  I'm more than 100 miles from a small town and 200 m from a large one with RV repair. But I can get on the phone to see where I'll get a repair.   I've removed the gray cover over the regulator....there seem to be two 'regulator-type' insertions along the horizontal from the gas valves (internal and external) to the coach appliances. Does that mean I have a 2-stage regulator?  I'll go back through the manual and see what I'm missing here.  

A little history:  I was running all appliances on house propane and it ran out...leaving air in the line.  When I hooked up my auxiliary tank and fed new gas through the line, the stove came on ok and the fridge burner lit but never cooled the fridge again.  That's when I took the fridge burner apart and cleaned it. I don't know if my running out of gas was coincident or causal with the fridge breakdown.  

Thanks...nan

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Excellent. Thanks for forwarding that to me. How do I determine that replacing the regulators is the next step?  Process of elimination?  Everything else seems to work fine, so the regulators are the next logical point of breakdown?

I've been studying the 2652 Diagnostic Service Manual and there are a couple other things I probably need to do, like clean the flue, replace the door seal, re-check all the gas lines for restrictions....

The regulators are inexpensive enough that may just be an easy step to take.   Thanks again.....

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When you connected the external tank to the system, did you shut the valve to the built-in tank? If not, much of the LP & pressure may have been spent 'refilling' the built-in tank, causing a low-pressure situation. My first attempt would be to get my hands on another tank which is known to be full and working properly. Connect that with the house tank valve closed and see what happens.

It worked on the house tank. It didn't work on the external tank. Simple fix is to try another external tank. Little sense in starting to replace parts one by one until you can isolate what the exact problem is.

On a side note, is there a propane company near you that can come to fill your house tank onsite?

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I shut the valve to the house tank, then connect the external tank and slowly turn on the gas from the external. The fridge burner lights as soon as I turn on the gas setting on the fridge and it burns roughly the same whether I'm on the house tank or the cylinder.  I thought at first it ran better on the house tank, but after a number of tests, I really don't see a difference.  It will need to be tested with more precision.  I have another tank I can try.   And I'm recleaning and realigning the gas burner. 

I'll look for a propane store (not gas station) that can test my external tank for pressure.  I found someone to replace the regulators if that's an appropriate step.

 

N

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Nan,

I hate to "diagnose by throwing parts at it", but cost of a new regulator is probably about the same as testing. And, at 11 years old, probably a good preventive maintenance move.

Agree, this may not be the problem with the refrigerator,  but eliminates one of the causes of poor performance on propane (low gas pressure means small flame means poor cooling).

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I'm cooling the burner unit and taking it apart again.   I'll check back in after I've run all the tests and cleaned everything.......thanks.

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Nan --

Sorry to hear you are having problems with your frig.  Having read through all of the great replies above have you checked that the chimney above the burner has no obstructions?

Most RV refrigerators have an aqueous ammonia based cooling system (see attached diagram).  Heat is required to boil the ammonia out of the ammonia-water solution (ammonia vapor is the refrigerant for the frig much like the Freon is the refrigerant for your dash A/C).  The source of that heat is either the 120 volt heating element or the propane burner (see the attached diagram).

Your frig works fine on 120 volt which means the electric heating element has good contact with the boiler/perk tube and the heat input is adequate.

Your describe the propane burner as working "OK" regardless of using propane from your on-board tank or external tank.  My suspicion is the chimney above the burner is restricted with cobwebs/dirt or a bird's nest or something else meaning inadequate hot gas flow along the boiler/perk tube.  Typically the chimney "exhausts" through a rectangular opening through the top of an RV's roof.  The chimney has a rectangular cover to keep rain, branches, leaves, etc. out of the chimney.  To check the chimney I'd suggest removing the top cover and peer down into the chimney with a suitable flashlight to look for an obstruction.  If there is an obstruction, a small width broom could be used to push the "stuff" out the bottom of the chimney.  Also  check the baffles in the bottom of the chimney above the burner to assure they are not partially plugged.

Hope this info is useful.

RV Frig Schematic.gif

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On my Norcold it was simple to clean the chimney, it was just like the picture above you pull the rod that is attached to the baffle,  Repeat the process several times than either blow out or vacuum the chimney.  You will have to remove the roof vent to access the chiminey from the top.

 

Jim

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3 hours ago, wolfe10 said:

If you do replace it, verify that the regulator is designed for HORIZONTAL INSTALLATION. The vent (screened part) needs to be perpendicular to the long axis of the regulator.  Said another way, you do not want a regulator designed for vertical installation.  Price is the same, but they are NOT interchangeable.

This may be a gotcha, the coach tank is horizontal, the add on cylinder is vertical, it seems to me that the extend a stay should have been placed in line after the built in regulator and then use a regulator at the add on cylinder. Maybe not true, but if the regulator for onboard is for horizontal only, then there may be a restriction there. The flame on the stove may not be as obvious as the fridge because of the size of the flame.

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