Freezer works, fridge does not.

[Scovndrel]

Hello!

I have a 2017 Travel Lite 625SL truck camper that I bought new.
The fridge/freezer unit which is a Dometic RM2354, mfg 2016, worked OK when I bought it, but never as well as the larger units in two other rigs I've owned. It got intermittent for a while, and now it is consistently bad.

I have a digital thermometer with an external probe that I jammed into the fridge through the thermistor hole, so I can check the temp without opening the door. It agrees within a few degrees with the analog one that is inside the fridge.

The problem is that while the freezer can freeze things and keep them frozen, the refrigerator portion does not get very cold, depending on the outside temp. For example, this morning we got a little frost on the roof of our house, and the RV fridge was at 35 degrees. On warmer days (65 to 75 degrees), the fridge gets to about 55 or 65 degrees, only a few degrees below the ambient air temp outside. But the ice packs in the freezer are still frozen solid. The cold just is not making its way into the fridge section well.

I am testing in my driveway. The fridge is perfectly level according to the bullseye level inside the fridge.

I have moved the thermistor clip to different areas on the fins, though my understanding is that this is a maximum of 5 degrees variance, not enough to cover what I am seeing.
The thermistor, when dunked in a glass of cold water with crushed ice, reads 9370 Ohms - right in "the zone". After reading a bit, I have now left the thermistor unplugged and we'll see what happens - it has been about an hour since I unplugged it.

There has never been an ammonia smell nor any yellow residue.

I have very little stuff in the fridge, so there is no air circulation blockage.

I have a little solar fan blowing on the condensor. It doesn't seem to make any difference. I have tried a battery powered fan inside the fridge. No difference.

It doesn't seem to matter whether it's on shore power or propane; in either case the chimney gets hot, the freezer stays frozen, and the fridge is tepid.

I have inspected the door seal. It is tight all the way around.

While I did not measure clearances exactly, I looked at the diagrams in the manual, and the fridge compartment looks pretty much the same as every RV fridge compartment I have looked at.

So, anyone have ideas what the heck is going on?
How, exactly, is the cold supposed to enter the main refrigerator compartment? Does it trickle down from the freezer, or is it a separate mechanism, attached to the cooling unit independently from the freezer?

[Chum_lee]

"OP Freezer at 10*F and food compartment at 45*F running with thermistor unplugged..."

Unless you are operating in high temp conditions, your Dometic freezer unit should have NO problems getting down to 0 degrees F.

IMO, both the refrigerator and the freezer sections are over temp and not cooling properly.

Chum lee

[Scovndrel]

Update: Did some searches on compressor conversion. Not really interested in going all-electric, no propane.

So I guess it's either remove the fridge and put in a portable cooler and a shelf to use that space differently, or buy a replacement cooling unit.

I'll give it some thought.
Thanks to everyone for the help going through yet another fridge cooling issue thread with me.

[Scovndrel]

OK, so I have an obstructed cooling unit.

Replace it with an Amish unit from rvcoolingunit.com or do a compressor conversion?

Amish unit is $515 after core refund. Read some reviews on it and sounds like a good idea. Sounds like it's not too tricky to do.

What are the costs for a compressor conversion? Is it a DIY job?

[Old-Biscuit]

hilke40 wrote:
It could still be the thermistor, even if ohms are okay as mine' 4 door was intermittent. Mine would always cool down when first turned on but would warm up sometimes a day later, or several days later, so the ohms were probably right. part of the time. It would be 0 in freezer and fridge would run 47 to 52. On mine the cooling unit test is to plug a working thermistor and leave the thermistor out in the compartment outside. It showed overnight 20 in top and 25 in bottom and froze a cup of water solid. On some models of dometic, unhooking the thermistor will make it cool constantly. There is a repairman from Washington on you tube that has a great video on how to install the upper fans, and baffles to direct air, as he says one manufacture doesn't have air directed correctly and the will never cool properly. My dealer thought I needed new control board, but the thermistor is what fixed it.

Your model will competely shutdown if thermistor is unplugged....
OPS....thermistor unplugged casues fridge to continuously cool.



OP Freezer at 10*F and food compartment at 45*F running with thermistor unplugged.....cooling unit has obstructions.
Running continuously with thermistor unplugged should have resulted in a freezer at 0*F (or lower) and food compartment at 32*F

'Burpping', 'flipping' 'rolling' a fridge to clear an obsruction is a stop-gap/band-aid at best.
Obsructions are due to the sodium chromate turning to crystals from overheating. The crystals are hard as weld slag/permanent (do not dissolve/go back into solution----just get banged loose and move somewhere else inside cooling unit tubing)
If you go to all the trouble of removing fridge....FIX it
**New cooling unit----Compressor system conversion----new fridge
WHy do it all over again?

[ScottG]

hilke40 wrote:
It could still be the thermistor...

The OP unplugged the thermistor so that cannot be it.

[hilke40]

It could still be the thermistor, even if ohms are okay as mine' 4 door was intermittent. Mine would always cool down when first turned on but would warm up sometimes a day later, or several days later, so the ohms were probably right. part of the time. It would be 0 in freezer and fridge would run 47 to 52. On mine the cooling unit test is to plug a working thermistor and leave the thermistor out in the compartment outside. It showed overnight 20 in top and 25 in bottom and froze a cup of water solid. On some models of dometic, unhooking the thermistor will make it cool constantly. There is a repairman from Washington on you tube that has a great video on how to install the upper fans, and baffles to direct air, as he says one manufacture doesn't have air directed correctly and the will never cool properly. My dealer thought I needed new control board, but the thermistor is what fixed it.

[Scovndrel]

Well, after running for 12 hours with the thermistor unplugged, the fridge is still at 45 degrees. Ambient temp outside is 47 degrees right now.

The freezer is at 10 degrees, ice packs are still frozen solid. Every time I touched the chimney today it was hot, every time I touched the 120 heating unit it was almost hot enough to burn after a 1-second touch.

It seems hardly necessary to plug the heater leads into the 120V directly. If the controls were turning off the heat improperly, the freezer would not be staying cold. So plugging the 120V heating leads directly into the outlet bypassing the controls doesn't seem like it will do anything.

In doing some more searching specifically on the freezer getting cold while the fridge stays warm, it really seems like I have a blockage in the cooling unit.

It is suggested on some other forum threads that I take the fridge out and lay it on each side for a few hours in an attempt to dislodge the blockage, which may help temporarily, or possibly for a very long time if the flakes settle in the bottom. Or buy a refurbished cooling unit, which seems to me like a better plan. Anyone know if you still have to pull the fridge to replace that?

[ScottG]

OB is not talking about an obstruction in the chimney. He's talking about a clog in the cooling unit itself.
Do exactly what he describes: Unplug the fridge, disconnect the heater and connect the heaters leads directly to 120VAC.

[Scovndrel]

Old-Biscuit wrote:
Insufficient cooling on both heat sources is one of three things
*Ventilation ----- draft/airflow is obstructed across backside of fridge (insultaion fallen down, top vent obsctructed/birds nests, etc)
*Thermistor ------ even when ohms are within range they still can be bad
(Unplug and run firdge for 12 hrs minimum then check temps)
*Cooling Unit ---- obstruction/blockage between freezer coil and food compartment coil. Freezer gets ALL of the cooling effect and food compartment is minimal.
(Unplug electric heat element leads from lower circuit board. Plug the leads DIRECTLY into the 120VAC Outlet and run fridge for 12 hrs minimum. This is 'forced' cooling....bypassing ALL controls. If cooling unit functions both compartments will get COLD. If cooling unit obstructed only freezer will continue to get cold.

Hopefully...bad thermistor.
Replace with a 'Snip-The-Tip'

Otherwise...cooling unit DEAD



AS for MOVING thermistor on FIN.
YOUR Model has Temp Settings (1-5)
Put the themistor BACK where it was (OEM Position--middle of fin)
Make sure the tip is just protruding above top of clip and it is secure against the Fin

Moving the thermistor UP/DOWN is for those Models that use an 'AUTO TEMP CONTROL' (no temp setting adjustments)
NOT your Model

I forgot to mention, I verified that the chimney did not have any obstructions a long time ago when I first started troubleshooting this. I have been lazy and this has been a problem for a while now. Beyond that, the area behind the fridge is quite clean and unobstructed. Insulation is where it should be, no bird nests :), the screen on the top vent is intact, checked when I installed the fan back there running to a solar panel on top of the vent cover, so nothing has gotten in there to chew things up. So I am pretty sure I do not have an external obstruction.

I'm having trouble with the concept that the thermistor could provide the correct resistance and still be bad. Its function is to provide a certain number of ohms of resistance back to the board. If I plugged my multimeter into the ends of the wires where they plug into the board and the ohms check out, how can the thermistor still be bad? Believe me, I WANT it to be a bad thermistor. But I don't see how. Further detail on that: When I first hooked up my meter the fridge temp was about 40 (had been 35 until I opened the door), and the thermistor was reading about 6500 ohms roughly. I wrapped my hand around the tip of the thermistor for about 30 seconds to warm it up and checked the reading again and it had dropped to about 5000-ish. Then I dunked it in the ice water and watched the numbers on the meter start to rise. After about 10 minutes it had settled at 9370, with the occasional twitch of about 10 ohms either direction.

I will check the fridge tonight after the thermistor has been unplugged for 12 hours.
If the fridge has not responded as expected for a bad thermistor I will see about plugging those leads directly into 120V (I will remove shore power first, plug them in there carefully, and then re-apply power.) and give it another 18 hours. Would just do 12 but ambient temps are pretty low this time of year here so I want to see if it stays cold when the sun comes up. Should have gotten around to this testing sooner.

Thank you for the additional testing steps to try. And I'll put my thermistor and clip back where it belongs, thanks.

[Scovndrel]

wa8yxm wrote:
On my Fridge (Also Dometic) I added two fans outside blowing up (4" computer fans they run all the time) and two more (Also 4") on the top shelf blowing towards the rear to circulate air.. ONE of them blows harder than the other and actually does a fair job of keepign the fins on the thermistor end frost free!!!

There is a kit you can get (about 100Bucks) includes both fans and lights mounts to the top of the fridge compartment.. CW among others sell it. I'm thinking of getting one because of the nuisance factor of what I use now.

Will decide tomorrow when I go shopping.

My Fridge currently is non-op awaiting repair next week. Thankfully I have a stand-alone ice maker, a second freezer and a coleman ice chest. Cooler.

Thank you for the ideas. I may hook up a fan on the fins on the inside connected to a little solar panel on the roof at some point, once basic functionality is restored, so I can pack more into the fridge. But I'll wait on that until I know whether I'm replacing it or not.

[Scovndrel]

Old-Biscuit wrote:

ksg5000 wrote:
Make sure the humidity switch located in the door jam isn't turned on - that provides power to heat tape which may eventually impact cooling capacity - also make sure your fridge light bulb is turning off when you close the door. Make sure there is adequate air flow behind the fridge. Also suggest you use YouTube and check burner orifice and baffle. If all that doesn't fix issue then it's possible you have partial blockage of the cooling unit - that usually is the beginning of the end but there are temp fix (google).

OPs Model does NOT have that feature.

Thank you for saving me the time I would have spent searching for that. Pretty sure I don't have a light bulb either. Will double check next time I go out there.

[wa8yxm]

On my Fridge (Also Dometic) I added two fans outside blowing up (4" computer fans they run all the time) and two more (Also 4") on the top shelf blowing towards the rear to circulate air.. ONE of them blows harder than the other and actually does a fair job of keepign the fins on the thermistor end frost free!!!

There is a kit you can get (about 100Bucks) includes both fans and lights mounts to the top of the fridge compartment.. CW among others sell it. I'm thinking of getting one because of the nuisance factor of what I use now.

Will decide tomorrow when I go shopping.

My Fridge currently is non-op awaiting repair next week. Thankfully I have a stand-alone ice maker, a second freezer and a coleman ice chest. Cooler.

[Old-Biscuit]

ksg5000 wrote:
Make sure the humidity switch located in the door jam isn't turned on - that provides power to heat tape which may eventually impact cooling capacity - also make sure your fridge light bulb is turning off when you close the door. Make sure there is adequate air flow behind the fridge. Also suggest you use YouTube and check burner orifice and baffle. If all that doesn't fix issue then it's possible you have partial blockage of the cooling unit - that usually is the beginning of the end but there are temp fix (google).

OPs Model does NOT have that feature.

[Old-Biscuit]

Insufficient cooling on both heat sources is one of three things
*Ventilation ----- draft/airflow is obstructed across backside of fridge (insultaion fallen down, top vent obsctructed/birds nests, etc)
*Thermistor ------ even when ohms are within range they still can be bad
(Unplug and run firdge for 12 hrs minimum then check temps)
*Cooling Unit ---- obstruction/blockage between freezer coil and food compartment coil. Freezer gets ALL of the cooling effect and food compartment is minimal.
(Unplug electric heat element leads from lower circuit board. Plug the leads DIRECTLY into the 120VAC Outlet and run fridge for 12 hrs minimum. This is 'forced' cooling....bypassing ALL controls. If cooling unit functions both compartments will get COLD. If cooling unit obstructed only freezer will continue to get cold.

Hopefully...bad thermistor.
Replace with a 'Snip-The-Tip'

Otherwise...cooling unit DEAD



AS for MOVING thermistor on FIN.
YOUR Model has Temp Settings (1-5)
Put the themistor BACK where it was (OEM Position--middle of fin)
Make sure the tip is just protruding above top of clip and it is secure against the Fin

Moving the thermistor UP/DOWN is for those Models that use an 'AUTO TEMP CONTROL' (no temp setting adjustments)
NOT your Model

[ksg5000]

Make sure the humidity switch located in the door jam isn't turned on - that provides power to heat tape which may eventually impact cooling capacity - also make sure your fridge light bulb is turning off when you close the door. Make sure there is adequate air flow behind the fridge. Also suggest you use YouTube and check burner orifice and baffle. If all that doesn't fix issue then it's possible you have partial blockage of the cooling unit - that usually is the beginning of the end but there are temp fix (google).