Dometic Will Not Cool on DC

[Esther315]

I have a 2007 Casita SD

The Dometic refrigerator is a 3-way Dometic model RM2454
It cools to 33 on AC. Same for LP



I want to use the dc power mode on occasion.


It will not cool at all on DC, even when trailer is connected to 30A, and batteries fully charged (this was our test mode).
After 12 hours, thermometer reads ambient temperature (74F)
We use a power ventilator, and it was on.
Freezer is not cold, compartment is not cold.



The DC light stays on, and the check light DOES NOT COME ON.


I know the pros and cons of using DC while towing, so no need to bring these up.


Just need advice as to how to troubleshoot or repair.

[Raz]

Realizing long distance trouble shooting is a crap shoot.....

With the fridge on DC for a while, put your hand on the chimney.

-warm? DC heating element may be going bad

-cold? DC element circuit is open. With a volt meter, measure the voltage at the element .

If you measure the battery voltage, the element is most likely open. With power disconnected, measure the element resistance. I would guess a good element would be around 1 ohm but the manual will give you an exact number.

If you measure no voltage, then there is an open between the battery and the element. Most likely a bad connector, open fuse, or bad switch.

Good luck, Raz

[Doug Arthurs]

Yes check the chimney see if it's warm. Could it be a fuse? I see you mention a light on so probably not but don't go down to many troubleshooting trails until you have check the basics.

[steve dunham]

Originally Posted by genesis315

I have a 2007 Casita SD

The Dometic refrigerator is a 3-way Dometic model RM2454
It cools to 33 on AC. Same for LP



I want to use the dc power mode on occasion.


It will not cool at all on DC, even when trailer is connected to 30A, and batteries fully charged (this was our test mode).
After 12 hours, thermometer reads ambient temperature (74F)
We use a power ventilator, and it was on.
Freezer is not cold, compartment is not cold.



The DC light stays on, and the check light DOES NOT COME ON.


I know the pros and cons of using DC while towing, so no need to bring these up.


Just need advice as to how to troubleshoot or repair.

The refrigerator has 2 electrical heating elements , one works on 120 VAC and the other works on 12VDC also there is a 12 VDC fuse for the refrigerator in the converter . I would check the fuse first and if that’s good then the 12 V element
The elements are inexpensive and not difficult to change out

[Esther315]

I understand that trying to diagnose from a distance is indeed a crap shoot, but if it is used for telemedicine, I am very willing to accept advice that is free.

I will check these out and advise as to what I find.

[redbarron55]

Check the current draw. If it is not drawing current there is an open circuit, if it is low then a poor connection. Perhaps a bad ground if you are measuring 12 or 13.5 on the input.

[Esther315]

Column was cold.

The 30 amp fuse in the lower compartment was fried, as well as its case.
It was not touching any heat source.
It appears that someone replaced the fuse in the past, and spliced the wire with a lesser gauge wire from the fuse case to the 12v terminal block (a red wire).
The wire leading to the case is orange.



They spliced the fuse case with orange on one side, and ran red to the terminal block.
Does anyone know the proper gauge of wire to use to connect the fuse to the 12v terminal block? Color?
Should I guess orange? 8 guage?
Really want to know. Don't want to do this again.

[wilyoung]

Originally Posted by genesis315

Column was cold.

The 30 amp fuse in the lower compartment was fried, as well as its case.
It was not touching any heat source.
It appears that someone replaced the fuse in the past, and spliced the wire with a lesser gauge wire from the fuse case to the 12v terminal block (a red wire).
The wire leading to the case is orange.



They spliced the fuse case with orange on one side, and ran red to the terminal block.
Does anyone know the proper gauge of wire to use to connect the fuse to the 12v terminal block? Color?
Should I guess orange? 8 guage?
Really want to know. Don't want to do this again.

My only experience with telemedicine included video. A picture would help.


That being said, is sounds like a lot of heat was generated around that fried fuse. This may indicate a short to ground somewhere. I'd disconnect the ground wire at the heating element and check resistance to ground at the fuse end of the hot wire before hooking things back up. The ground wire at the heating element because the element itself may be shorted to ground. If you do get a short indication then disconnect the hot wire at the element. If the short is still there something is wrong with the wiring; happy hunting. If the short goes away it's probably the element.


If there is no short to ground it may be that someone used too small a wire to hook-up the fuse. Right off hand I don't know the wire size for 30 A, but you should be able to find a DC wire size chart that would tell.

Good luck

[Esther315]

Attached is a photo of the 30A fuse. The holder is also melted.
Before the yellow sleeve, the wire is orange. (Doesn't look like it in the photo)
After the yellow sleeve and to the terminal block, the wire is red.
The orange and yellow wires don't appear to be the same gauge.


Doubt if this is factory wiring, but prior owner never mentioned any problem.
I have had this unit for 5 years without any DC refrigerator problem.


I know I have to replace the fuse.

Is the correct fuse case shown?
It also looks like the wire needs to be replaced. If so, what gauge/color (?orange)
Finally, is there an underlying issue that caused the problem in the first place?

[gordon2]

Originally Posted by genesis315

Attached is a photo of the 30A fuse. The holder is also melted.
Before the yellow sleeve, the wire is orange. (Doesn't look like it in the photo)
After the yellow sleeve and to the terminal block, the wire is red.
The orange and yellow wires don't appear to be the same gauge.


Doubt if this is factory wiring, but prior owner never mentioned any problem.
I have had this unit for 5 years without any DC refrigerator problem.


I know I have to replace the fuse.

Is the correct fuse case shown?
It also looks like the wire needs to be replaced. If so, what gauge/color (?orange)
Finally, is there an underlying issue that caused the problem in the first place?

That can happen when the electrical connection between the fuse and fuse holder is bad and has high resistance. So maybe after it got knocked loose at some point, it melted when you ran your test. So first cut out the melted fuse holder. The good news is that if you have voltage on the hot wire that went to the fuse, the repair should be easy. If not, work your way backwards.

Inline fuse holders come with pig tail wires and different color leads from the fuse holder (compared to the wires they attach to) are not at all uncommon. And they are often smaller gauge, but since its only a few inches going down one gauge size should be OK. Resistance is affected by gauge and wire length (and to a lesser extent some other factors).

[redbarron55]

The refrigerator draws about 10 amps constantly and a poor connection on the blade type fuse holder generated the heat, dissipating the power right at the connections which caused the melting of the fuse before it gave up. My guess is that the 30 amp fuse is oversized.
The refrigerator probably draws about 12.5 amps and I don't think that it operated on the thermostat like the PL and 120 VAC and the power going to the 12 volt heater is less than either.
Fuses should be about 120 to 150% of the constant load which would indicate a 15 or 20 amp fuse, 20 being more nearly correct.
The fuse protects the wire from over heating and the wire should comfortably carry more than the fuse is rated for. #10 AWG would be OK, nothing wrong with #8.
Of great importance is good connections, both in any terminals, splices and the actual grip the fuse holder puts on the blades.
Probably best is to use the same size as the manufacturer used when they built the unit.

[Esther315]

Ok. I get it. You are correct. We have an inline voltage regulator and have measured Amp usage (so we don't run AC/microwave/electric hot water/drip coffeemaker simultaneously). We have a wall chart.


The wiring diagram in the original owners manual specifies a 30A fuse for the DC component in that location. I don't understand why.
Will replace with a 20A
Thank you.

[wilyoung]

Originally Posted by genesis315

Attached is a photo of the 30A fuse. The holder is also melted.
Before the yellow sleeve, the wire is orange. (Doesn't look like it in the photo)
After the yellow sleeve and to the terminal block, the wire is red.
The orange and yellow wires don't appear to be the same gauge.


Doubt if this is factory wiring, but prior owner never mentioned any problem.
I have had this unit for 5 years without any DC refrigerator problem.


I know I have to replace the fuse.

Is the correct fuse case shown?
It also looks like the wire needs to be replaced. If so, what gauge/color (?orange)
Finally, is there an underlying issue that caused the problem in the first place?

OK. A picture's worth a thousand words. I thought you indicated that the wire was also hot (thermally). It looks like the heat was limited to the fuse holder so loose connection between fuse and holder is probable cause. Cancel my previous short to ground theory. Install new fuse holder and give it a go.


Edit: If the wiring diagram specifies a 30 A fuse that's what I would use. You may blow a 20 A unnecessarily. It depends on what all that circuit feeds.

[Raz]

Here's a link to the installation/operation manual for a Dometic RM 2454. Page 8 covers DC installation including wire size. Page 13 specs the inline fuse at 30 amps.

http://www.manualslib.com/manual/254...54.html#manual

[redbarron55]

Of course it has no bearing on this issue, but my Norcold DE 490 has a current draw of less than 4 amps on 12 volt DC.
And it doesn't use any LP gas...

[Raz]

Manual says both heating elements are 175 watt, so the 12 volt element will draw about 15 amps. Add a couple for a controller, so I guess a 30 amp fuse is not unreasonable. That said, I would suggest that the blown fuse is a symptom, not the problem.

[RogerDat]

That fuse doesn't look like it blew from a short, it looks like what several have suggested poor connection right inside or at the fuse holder. There looks to have been excessive resistance that created a hot spot right there.

Have seen something similar once before. Corrosion on the clips for a glass barrel fuse. The fuse didn't look burned out BUT the wire was melted back under the metal end cap. New fuse got pretty hot on the end pretty quick. Cleaned clips and all was cool again.

I would replace the fuse holder, maybe buy one with 10 gauge wire. During your test feel that new holder for heat.

I believe the heating elements are typically the same ones for 110 volt and 12 volt so if it works on one it probably isn't the heating elements.

IF the new fuse holder and fuse blow you have a short, if even with a good connection the holder gets hot you are drawing too much current or have too much resistance on that wire or circuit. Then I would be poking around with a meter trying to find out where.

[redbarron55]

The heating elements cannot be the same as the resistance of the 120 volt would be quite a bit higher than the 12 volt for the same power.
If they are the same the current would be quite a bit less for the 12 volt unit.
They may both be 150 watt.

[Esther315]

This is the second time that this fuse has burned out, though the last time was over 5 years ago.
Do I have to open the column to access the wires I need to test for a short?
Looking at the wiring diagram, I am not sure the location of the ground wire.

[stevebaz]

You have to get to the heating element to check for short from wire to case of the heater cartridge. Their should be no short from either wire to the cartridge case.