Dometic RM2453. LP good, AC freezes, nothing on DC.

[pjw73nh]

Dometic RM2453. Works fine on LP, freezes on AC and does not appear to do any cooling on DC. I know from what the previous owner told me that the AC heater was replaced last year.

I am using the following diagram for troubleshooting.I am also using the Dometic troubleshooting manual.

Schematic

I am just getting around to writing this now. But based on my observations from the summer (and if I remember them correctly), the fridge operates as mentioned above.

I am pretty sure I have a shorted thermostat but would like a second opinion. Not only is the part quite expensive, but being installed a Roadtrek, this fridge is a real PITA to remove to gain access to the thermostat. If in fact, I need to remove to to get to the thermostat.

It's rather cold up here in the northeast today (11/11/2-17), but I figured it's a good environment to test for a thermostat short, because if anything, it would be too cold and the thermostat would be satisfied (open). I made two sets of tests today.

The first set was done with the inside of the fridge at about 25 deg F. Then I turned to fridge on AC for a few hours and brought the inside temp down to 5 deg F and did the second round.

Outdoor ambient is around 35 deg F, internal fridge (not freezer) temp is about 25 deg F. In AC mode, with the thermostat knob all the way counterclockwise (off) with an inductive clamp-on ammeter directly on the AC heater lead, I measure 1.5 amps flowing to the AC heater. Turning the thermostat knob full on makes no difference in current flow. Turning the selector switch from AC to off reduces current flow to 0 amps as expected.

Performing the same test with the same environmental conditions but in DC mode and measuring the DC heater, yields similar results. The only difference is that the current flow when on DC is 15 amps. Again, the thermostat control has no effect and switching the mode selector from DC to off kills all current flow to the DC heater.

As mentioned, I repeated these same procedures with the internal fridge temp at 5 Deg F and I received the exact same results. The current NEVER stops flowing to the heaters in either mode at either internal fridge temp.

If I recall correctly from the summer, gas operation works properly.

I don't see any schematic information for the gas operation. The manual mentions that the thermostat is "calibrated by the manufacturer to maintain a 40 deg temp" in the fridge. But at the same time it says that temp can be controlled by the thermostat when is gas mode. What is the mechanism that turns the flame on for cooling, and off for pilot (standby/bypass) operation?

Summarizing my issue:

1. Does it sound like a defective thermostat? Do they go bad? Often? In 30 years of RVing, in 6 different rigs, I've never had one go bad. From the schematic, I can't see it being anything else.

2. If it IS the thermostat, is there any means of accessing it without removing the fridge? What about the little capillary sensor? How is that routed into the fridge?

3. Why might it not cool on DC mode, when in fact, there's current flow? I am thinking when they replaced the AC heater, they might have mis-positioned the DC heater, and it just doesn't get close enough to the boiler for effective heat transfer.

Any thoughts or suggestions welcome.

Thanks.

P.../NH

[pjw73nh]

Well... Three years later I have some new information. I have taken no action and just lived with the situation the way it is/was.

New findings: Contrary to the post title. Whether on AC or LP everything freezes. This is regardless of thermostat knob position (even in the "off" position). Unless it's REALLY REALLY hot outside day and night. Then it pretty much keeps up fine. Cooler days and nights? It freezes.

I gave up using it on 12V. Not worth my time and aggravation. It may or may not work.

Hopefully still waiting on some updated schematic documentation.

[pjw73nh]

Hi Doug, we're getting closer..

Dougrainer wrote:
1. It is NOT the size wire gauge for SAFETY. It is the SIZE wire gauge to adequately transfer FULL 12 volt power to the refer. The smaller the wire gauge the LESS 12 volt power is transmitted to the 12 volt element.

Wouldn't you think that if 10 ga wire can support -100 amps- of 12 volts at 7 feet, it would be enough for the 12v, -16 amps-, 6 feet that the my fridge draws? After all, 100 amps is more than 6 times what my fridge draws.

Dougrainer wrote:
2. You have as BYPASS tstat. That is why it freezes on 120 and cools correctly on LP. The POINTS in the 120 side of the tstat are welded/stuck together and the unit runs 24/7 on 120. You need a new tstat to fix the 120 problem. IF you have a silver metal capillary tube inside on the evap fins the tstat I linked too is the correct tstat. It is a 120 and LP ONLY tstat

I don't know what a "BYPASS" thermostat is when referencing refrigeration. I have only seen the term used in automotive coolant thermostats. Can you help me with this? Yes, I do have the capillary tube running on to the fins. and Yes, line voltage is 122vac.

Dougrainer wrote:
3. Regardless of what the OEM did does NOT make the original install correct. Chinnok motorhomes were about the same size as yours and their Dometic 3 way refers had 8 gauge wire to the refer from the battery.

The Installation manual for the fridge calls for 10 gauge wire up to 17 feet from battery, and 8 gauge wire for up to 27 feet.
RM2453 Install manual Page 8.

Dougrainer wrote:
5. I doubt the element sleeve has come loose. That is extremely rare, I have only seen 1 in 38 years.

I would tend to agree. I guess the only way I'll find out is to take it apart and have a look-see.

Dougrainer wrote:
Your model does have the 12 volt thru the tstat, but this is what the instructions state.

This appears to be contrary to what you have stated in several posts previously.

This is your quote from the manual.

Dougrainer wrote:
DO NOT operate the refrigerator on 12 volt when the vehicle is parked. The amperage draw of the 12-volt DC heating element can discharge a battery in a very short time. The installation of a 12volt DC operated refrigerator requires a relay to be installed on the tow vehicle or in the caravan. The relay will automatically shut off the 12 volt DC power to the refrigerator when the ignition is turned off.

This is not relevant to my either of my issues but just to be on the same page, my Roadtrek does not have this relay in place and is not needed. I understand that if I leave the fridge on 12 V while parked, It will simply drain the HOUSE battery down NOT the vehicle's chassis battery. There IS a battery isolator installed that allows charging BOTH HOUSE and CHASSIS batteries while the engine is running, but when the vehicle's ignition is turned off, the chassis battery is no longer connected to the house battery, so it can't drain the chassis battery down and leave me stranded.

I think we agree on the fact that I need at least a new thermostat for the 120 VAC issue. As I mentioned earlier, I do believe it is shorted. I am going to have to wait until I can pull the sheet metal cover off the boiler area and check the 12v heater positioning.

I am going to try and contact Dometic and see if they can provide me with clarification of the tstat operation for all 3 modes. Or at least ask them what the LP open/close portion of the tstat mechanism is. It is not listed in the schematic, yet the manual mentions its use in the operation of LP mode.

I will update this thread as I find answers and resolutions to my issues.

Thanks.

[dougrainer]

1. It is NOT the size wire gauge for SAFETY. It is the SIZE wire gauge to adequately transfer FULL 12 volt power to the refer. The smaller the wire gauge the LESS 12 volt power is transmitted to the 12 volt element.
2. You have as BYPASS tstat. That is why it freezes on 120 and cools correctly on LP. The POINTS in the 120 side of the tstat are welded/stuck together and the unit runs 24/7 on 120. You need a new tstat to fix the 120 problem. IF you have a silver metal capillary tube inside on the evap fins the tstat I linked too is the correct tstat. It is a 120 and LP ONLY tstat
3. Regardless of what the OEM did does NOT make the original install correct. Chinnok motorhomes were about the same size as yours and their Dometic 3 way refers had 8 gauge wire to the refer from the battery.
4. While some 3 ways do have a tstat on the 12 volt side, that does NOT change the fact that the DC element is NOT for cooling down, only maintaining existing cold while in transit.
5. I doubt the element sleeve has come loose. That is extremely rare, I have only seen 1 in 38 years. Doug

Your model does have the 12 volt thru the tstat, but this is what the instructions state. Doug

DO NOT operate the refrigerator on 12 volt when the vehicle is parked. The amperage draw of the 12-volt DC heating element can discharge a battery in a very short time. The installation of a 12volt DC operated refrigerator requires a relay to be installed on the tow vehicle or in the caravan. The relay will automatically shut off the 12 volt DC power to the refrigerator when the ignition is turned off.

[pjw73nh]

Unit is original equipment in a 2003 Roadtrek Class B. I doubt Roadtrek would knowingly manufacture anything inadequate, or more importantly something that might be a safety or fire hazard.

1. Not questioning your credentials, You appear to have access to information that I don't that may be beneficial to my situation.

2. We will have to agree to disagree on wire size needed. 12V @ 15A at can safely run 10 feet with 18 AWG nevermind 8 AWG. 8 AWG can support 150A (conservatively) at 7 feet.

12V AWG wire capacities

3. I have 10 gauge wire (6 feet. 3 each way) to refer. More than adequate.

4. Unit is OEM to the motorhome. RM2453. I suspect a 2002-2003 manufacture date. No auto igniter. Piezo click to light.

Diagram here.


That part number is the same one shown in my manual (assuming my manual is correct, which at this time is in doubt) but I don't know for certain if that is my thermostat or not. I don't have the refer out of the motor home at this time so I can't see it. According to the description in the auction, it "says" it is the correct one. I won't know until spring when the Wx warms up and I have time to remove the refer. It is a several hour job in these small class B units to remove the fridge.

Could it be the manual I am using is incorrect regarding the correct operation of the 3 modes?

Could it be the schematic diagram in the manual incorrect?

Thanks.

[dougrainer]

1. MY advice is based on 38 years as an RV tech and still working
2. The SIZE gauge wire to the back of the refer is CRITICAL to 12 volt DC operation IF you do NOT have at least 8 gauge wire, then DC operation is futile.
3. WHAT size gauge wire is to the refer?
4. What Year refer is this? Does the refer have an auto ignition LP flame or do you have to manually click it to light? Doug

Look at this link. Is this your tstat?

https://www.ebay.com/itm/Dometic-2931336016-RV-Refrigerator-Thermostat-RM2453-RM2322-RM2333-/3913860...

[pjw73nh]

Art, Tnx for the reply. Agreed Schematic shows only ONE tstat.
Yes, I suspected the misplacement of the 12V heater in one of my earlier threads. Yes, not a good idea to weld on pressured ANH... Boom !

Doug,
First to answer your questions/recap.

1. LP? yes, works fine.
2. 120 AC? NO !! It freezes everything in both the freezer and the fridge compartments.
3. As the post title says: "LP good, AC freezes, nothing on DC"
4. See my answer to you in post #3 While camped or in transit (Transit)

Second, if

dougrainer wrote:
the tstat has no relation to the DC element. The DC element is wired direct.

why does the manual specifically mention (see my quote from the manual above) Thermostat mentioned the thermostat by name and reference number for operation in all 3 modes AC, DC, LP, AND include it in the schematic?

Where did you get your information that the DC heater DOES NOT go through the thermostat? I suspect this may have some valuable information for my situation. You seem have access to some information that I don't and that contradicts what I have from the manufacturer. If you could get this information to me, I would bet a paycheck that it also has a lot more updated information than I am currently working with. Thanks.

[dougrainer]

As I stated, the tstat has no relation to the DC element. The DC element is wired direct. BECAUSE, the DC element is a maintainer of existing temp. It is NOT designed to cool DOWN the refer. Now, the same tstat operates in both Gas and 120 mode. IF it operates on LP it will operate the same on 120. The ONLY variable for 120 operation is the line voltage. If too low(below 108) then the refer will not operate correctly on 120. Same if the LP burner is dirty or the LP pressure is NOT at 11.5 inches W/C.
So you need to recap.
1. Does the refer operate on LP correctly?
2. Does the refer operate on 120 correctly?
3. If one mode does not, state what it does not do correctly
4. HOW are you attempting to operate on DC? Camped or in transit? Doug

[Rvpapa]

There is only ONE thermostat. From all that you have observed it sounds like the 12 volt heater is not in good thermal contact with the boiler. Perhaps it was not installed in the socket / tube that is on the boiler, or welds have been known to corrode and separate. If this is the case there is no simple fix. Rewelding on a closed system full of amonia is a sure way to ruin your day.
Art.

[pjw73nh]

Hi Bob, no offense taken, and I certainly appreciate the input but I would ask that you re-read my previous posts and examine all the information I have provided. Let's consider the facts (or perhaps better stated, the facts I have at my disposal) and what I have to work with.

1. I have a (presumably) accurate schematic.
2. I am not an expert in this field (hence my presence in this forum), but I consider myself pretty knowlegable and a pretty good troubleshooter.
3.There are some discrepancies presented by others here in this thread as to whether the schematic I have is, in fact accurate. An earlier poster mentioned a few things that would lead me to belive that there may be another, more accurate schematic than I have.
4.From my schematic and the troubleshooting manual for my model, and contrary to your mention, the amount of thermostats is unclear. The troubleshooting manual mentions (QUOTING):

From Troubleshooting Manual wrote:
GAS OPERATION
REFRIGERATORS WITH PIEZO IGNITOR
(RM2452 & RM2453)

To start the refrigerator, turn knob “A” to the “GAS” position.
Turn the thermostat knob “B” one-quarter (1/4) of a turn from the “OFF” position.
Push button “C”, push button “D” for the piezo ignitor several times to light the burner. This can be observed on the flame indicator “E”, on the refrigerator.
After the flame lights, continue to hold button “C” for an additional ten (10) seconds. Release the button “C” and check the flame indicator

ELECTRIC OPERATION
Check to be sure the power cord is properly connected to the power supply. If the refrigerator is equipped for 12 volt DC operation, the tow vehicle or caravan engine should be running to prevent discharging the battery.
Turn knob “A” to the position marked “ELEC” for 120 volt AC operation or “12V” for 12 volt DC operation.
Turn the thermostat knob “9” one-quarter (l/4) of a turn from the “OFF” position.
To shut off the refrigerator, turn knob “A” to the “OFF” position.

THERMOSTAT
The refrigerator is equipped with a thermostat that can be adjusted by turning knob “9” to a different setting to maintain the desired cabinet temperature.
“OFF” Setting of the Thermostat: In gas operation, the thermostat closes its main valve and the burner runs continuously at the bypass rate or pilot. In electrical operation, the contacts in the thermostat are open and the heating elements are off.

“MAX” Setting of the Thermostat: In gas operation, the thermostat allows the burner to remain on high flame continuously. In electric operation, the heating element is “ON” continuously.

The thermostat can be adjusted between “MAX” and “OFF” to obtain the desired cabinet temperature. The closer the knob is to “MAX”, the colder the cabinet temperature. The closer the knob is to “OFF”, the warmer the cabinet temperature.

When the thermostat reaches the set temperature, it will cut the burner back to bypass or, in electric operation, shut off the heating element.

THERMOSTAT LP GAS MODE
The thermostat is calibrated by the manufacturer so that at mid-range the cabinet temperature should be approximately 40 degrees Fahrenheit.

From the above, I gleen that the unit has ONE thermostat and that it controls all 3 modes of operation. AC, DC and LP.

3. Also contrary to your recent post, it DOES NOT work properly on AC it freezes everything (see OP). It DOES however, appear to function properly on LP.

4. 12V is not used for ANYTHING else on this fridge. Except secondarily, the voltage necessary to hold the LP gas solenoid open for proper operation when in LP mode. (the schematic I have shows NOTHING for this). There is no interior light and no circuit boards etc.

Summarizing, I believe I have two separate issues.

1. A shorted thermostat or the wiring pertaining to it.

2. A 12V cooling issue. I don't think they are related.

My conclusions:
1. Most likely a bad tstat. (But why does LP work fine).
2. I'm stumped. Electrical and resistive measurements check out ok and corroborate each other with 13.67V at the heater, and 15 Amps current and (newly measured .9 OHMS resistance). If it's not providing heat to the boiler, the energy in this circuit HAS to be going somewhere.

I am not trying to be argumentative. I am trying to provide as much pertinent information as possible in the hope that my situation could be explained/confirmed. My objective in posting was hoping that someone may have seen this (these) symptom(s) before and could shed some light on it/them.

Only the first issue makes logical sense, and If I had confirmation I'd be willing to go through the arduous and expensive task of removing the fridge and replacing the tstat.

The second one? I am at a loss.

Thanks.

[dougrainer]

BFL13 wrote:
Here is a link I have handy, that might be the one you already have. Anyway:

http://rvrefrigeratorrepair.com/wp-content/uploads/2016/07/Dometic-Service-AES.pdf

Do you realize that link is for a 30 year old Dometic? The Op's Dometic is not that model and the operational system is not the AES model system in the link. The AES system ONLY ran on 12 volt DC when the refer saw a 12 volt ignition signal from the Chassis Charge system or from the TOW vehicle Ignition system. Doug

[bob_nestor]

pjw73nh wrote:
Hi Bob, tnx for the reply. Yes, I saw that. I have the same manual. I have 13.67V at the heater. I have not measured resistance. I will try and do that tomorrow. But with the 15 amp current flow I must be pretty close to the .83 Ohms plus/minus 10% that they are looking for. I don't think there is another way of testing it (replacement $$). Would rather not spend the $$ unless I am CERTAIN that it is the issue.

I am still left with the thermostat issue even AFTER I fix the 12V issue.

No offense, but it seems like you're fixated on the thermostat and looking for confirmation before springing for the new one. It also seems you might be over analyzing the problem - a common thing many engineers often do. You need to find those components that are unique to the 12V cooling cycle and not used anyplace else. (Occam's Razor and the KISS principle are often overlooked when trying to solve complex problems.)

If the unit cools properly on AC and gas and it doesn't have two thermostats then you should be able to eliminate the thermostat. And with the testing you've done on the 12V you can probably eliminate that cause as well. The unit needs 12V for other things and with everything else seeming to work as expected then the 12V is probably not an issue. That only leaves you with the heater which is only used when cooling with 12V.

[pjw73nh]

Hi Bob, tnx for the reply. Yes, I saw that. I have the same manual. I have 13.67V at the heater. I have not measured resistance. I will try and do that tomorrow. But with the 15 amp current flow I must be pretty close to the .83 Ohms plus/minus 10% that they are looking for. I don't think there is another way of testing it (replacement $$). Would rather not spend the $$ unless I am CERTAIN that it is the issue.

I am still left with the thermostat issue even AFTER I fix the 12V issue.

[bob_nestor]

According to this Dometic document symptom 16 it's either DC voltage or the heating element. Don't think it can be the relay since that seems to only apply to the RM2610/RM2810 units.

[pjw73nh]

BFL13, Thanks for the reply. After seeing the link, at first I was excited because I hadn't seen it before and I thought YES!!!!! Better documentation. But then after looking at it, it is only for the larger, electronically controlled units. Mine is an older, smaller unit with no electronics (circuit boards). But thanks for trying I appreciate your effort.