odd refrigerator issue, Dometic

[centerline]

the unit is a Dometic 2852, it has always worked, but at times it wont get cold.... it will get cooler, but not cold on gas or electric.

sometimes it will get cold and work as it should.

all testing has been done on gas, with shore power disconnected from the trailer, and also on shore power alone with the gas off.

this unit had the automatic temp control with the thermistor clipped on to the fins in the fridge compartment... I thought it may be faulty so I replace it with the "Articca" adjustable thermistor from www.snip-the-tip.com...

this upgrade made a HUGE difference in how cold it gets when it gets cold, but it still has its problem of only getting cold sometimes.
when it works, the new adjustable thermostat will allow the fridge compartment to maintain 20degrees when the rest of the trailer interior is 80degrees... so im certain the fridge still has some useful life, if I can only find the intermittent problem.

the flame burns perfect and works great when it works, but it seems to be a thermistor problem and I dont know how the electrics work on these units or how the thermistor wires connect to the control panel, or if the board they connect to is bad, or where else the issue could be hiding.

im looking for suggestion as to how to further test it in an attempt to find the problem, or get it to fail permanently so that the local tech can find it.

thanks for any help you can offer..

[centerline]

I appreciate all the thought that is going into my cooling problem.... if anyone has doubts as to how cold its getting, I can take pictures or video of the readings.

the simple wall thermometer that I used normally hangs on the post outside my back door... when I brought it in the house, it read the same as my inside thermometer.
the industrial freezer thermometer I have been using is a certified thermometer. my intent has been to install it permanently so that I can monitor the interior of the fridge without opening the door to read an interior thermometer
its not difficult to read a thermometer and the thermometers are at least accurate within a degree or two....

I am positive that the aftermarket thermostat I installed is the reason it gets so cold now, as the original non adjustable thermistor did not allow it to get near as cold..

since we got back from our last trip (when the fridge quit cooling again) I have had the unit running for two weeks now without any issues.

with the suggestions I have gotten in an attempt to find the issue, I am more familiar with it, and about all i can do now is hit the road again and see if it remains working... if/when it quits working again, I have some knowledge of what I should be looking for. thanks for all the support.

[Old-Biscuit]

dougrainer wrote:

Old-Biscuit wrote:

drsteve wrote:

dougrainer wrote:
I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

The OP stated that the problem was there before he installed the aftermarket thermistor. I'm still trying to figure out how the freezer hits -24F.

Yep...
OP changed the thermistor to a rheostat replacement because CU wasn't cooling...then it was cooling...then it wasn't ....then it is again

Cooling unit is DYING

A dying CU will not perform as the OP's. When it works, it works TOO GOOD, for a marginal or bad CU. Doug

TOO GOOD......exactly
When have you ever measured -24*F in a freezer even when being 'forced cooled'?

[dougrainer]

Old-Biscuit wrote:

drsteve wrote:

dougrainer wrote:
I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

The OP stated that the problem was there before he installed the aftermarket thermistor. I'm still trying to figure out how the freezer hits -24F.

Yep...
OP changed the thermistor to a rheostat replacement because CU wasn't cooling...then it was cooling...then it wasn't ....then it is again

Cooling unit is DYING

A dying CU will not perform as the OP's. When it works, it works TOO GOOD, for a marginal or bad CU. Doug

[dougrainer]

drsteve wrote:

dougrainer wrote:
I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

The OP stated that the problem was there before he installed the aftermarket thermistor. I'm still trying to figure out how the freezer hits -24F.

His original Thermister was a preset temp. Just because he changed to an aftermarket does not mean THAT new Thermister is not OK. He could have had the original bad, if he had replaced with OEM part, then that takes that out of testing. Doug

[Old-Biscuit]

drsteve wrote:

dougrainer wrote:
I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

The OP stated that the problem was there before he installed the aftermarket thermistor. I'm still trying to figure out how the freezer hits -24F.

Yep...
OP changed the thermistor to a rheostat replacement because CU wasn't cooling...then it was cooling...then it wasn't ....then it is again

Cooling unit is DYING

[drsteve]

dougrainer wrote:
I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

The OP stated that the problem was there before he installed the aftermarket thermistor. I'm still trying to figure out how the freezer hits -24F.

[dougrainer]

I would say your after market Thermister system is the culprit. Since your test show a fully functional CU, the only thing that is a variable is a NON Dometic part---The aftermarket Thermister. THAT controls when and how the Refer cools. There are NO moving parts in the Cooling unit, all it takes is Gravity(being level) and HEAT to function. Doug

[dougrainer]

Your Thermometers are not accurate or you are not reading them correctly. There is NO WAY you could get -24 in the freezer, unless your version of -24 is 8 degrees----32-24= 8. Doug

[Old-Biscuit]

drsteve wrote:

centerline wrote:
.

im going to let it run at this setting this for a week to insure the best circulation, and hopefully dissolve any crystals/obstructions that may have been formed in the cooling system...

My understanding is that the crystallization is not reversible. If that is your problem, the cooling unit is dying.

Correct....

Once formed the sodium chromate crystals do NOT dissolve back into solution
They are PERMANENT and ACCUMULATIVE

[drsteve]

centerline wrote:
.

im going to let it run at this setting this for a week to insure the best circulation, and hopefully dissolve any crystals/obstructions that may have been formed in the cooling system...

My understanding is that the crystallization is not reversible. If that truly is the problem, the cooling unit is dying. The question I have is how is it getting that cold if it has a partial blockage...

[centerline]

I cleaned the cobwebs from the rear of the fridge and made sure the vent is free of obstructions from the bottom to the top..
then I removed and replaced all the wire connectors at the board in an attempt to make better contact between the pins and receptacles

and after further testing by placing the thermometer in a tub of water and letting it freeze there, with the thermostat set to its lowest point, Im getting 22 degrees on the middle shelf of the fridge... and in the freezer the temp is -24 degrees...

I am now using two different thermometers to check accuracy and they both read the same... one is a normal 5 dollar outdoor, old fashioned glass bulb type, and the other is an industrial round dial type with a 30" flexible remote wire so the thermometer can be outside the unit while its reading the temp inside...

im going to let it run at this setting this for a week to insure the best circulation, and hopefully dissolve any crystals/obstructions that may have been formed in the cooling system...

STILL, I see no need to bypass all controls and connect directly to the AC heating element, as the unit has been working for the past two weeks without quitting and has proven that it is fully capable of cooling down and staying cold.... AND the original problem was the same on gas as it was AC power... as to whether it will quit again when we want to use the trailer, that is yet to be found out...

[dougrainer]

The FINS which are very close to the top rack will be 10 degrees COLDER than the actual temp. So, put that cup of water in there and test the water. If you have a CU that works sometimes and does NOT, then you have a partial blockage. Your unit is 11 years old and you have no clue as to what the previous owner did with that RV. The fact you changed the tstat to an adjustable one will NOT make the refer run colder than it is capable of. What type of Thermometer are you using. A Dial round thermometer? A Digital Thermometer? OR a CHEAP generic refer thermometer? If the round Dial thermometer---CALIBRATE it. You put it in a glass of ICE water and then turn the dial to 32 degrees. Doug

[centerline]

dougrainer wrote:
1. I doubt when it IS working you are getting 20 degrees in the refer. RETEST the operation. The ONLY valid temp measurement is the temp of a glass of water after 24 hours. In 38 years as a tech, I have NEVER been able to get an RV refer below 25/26 degrees and that is with the Tstat bypassed.
2. HOW are you measuring the temp? With a glass of water or just laying a Thermometer inside?
3. The Correct temps should be BELOW 10 degrees in the freezer and below 36 to 38 degrees in the refer. LOWER temps in the refer are more common----28 to 32 degrees.
4. How old is the refer and are you the original owner?
5. The correct way to measure the performance of a refer is to run the 120 element direct, bypassing any controls for 24 hours. That will tell you the state of the cooling unit. Doug

laying the thermometer on the top rack, I get 22degrees, running on gas... I havent actually took a good reading of the thermometer when on AC...

there is no testing of a glass of "water" at 22 degrees, but I could check to see what happens by setting the thermometer in a glass of water and then checking the internal temp of the glass of ice in about 12 hours.

when it is working, and with the thermostat turned down, it only takes about 5hrs for the fridge compartment to come to freezing from 70 degrees.... I have not checked to see what the freezer temp is, but it is definitely cold...

the unit is an '07, and I am the second owner.. the entire trailer was used very little before I purchased it and was just setting for the past 6 years without any use at all..

the reason I have not tested the unit directly at the ac element and bypassing the controls is because when its working and cooling, it can work for WEEKS just fine on AC or gas, which tells ME the cooling unit is capable of doing what it is supposed to do...

I will be checking the venting and the thermostat connection to the board today..

[Old-Biscuit]

Your cooling unit is DYING..........

There is no 'saving' it.

There is nothing you can do to 'repair' it.

Cooling unit has internal obstructions/blockages that disrupt the internal flow of coolant.

Prime example of those that 'flip' a fridge, bang on tubing, drive on rough bumpy roads and then fridge starts cooling again........for a while.

Cooling unit is DYING.