I have a Dometic S630 absorption fridge from 1991. AFAIK newer ones work the same way. Apparently the freezer cools down and then eventually the fridge cools down to its proper temp range just above freezing.This works ok when on propane. My 120v heater is irreparable.When I use my jury-rigged AC method powering the 12v heater with 12v (15.2v actually to get the watts needed) from a converter on its 120v input, I get 200w instead of the 300w that the 120v heater would do.With colder ambient outside, this 200w is enough to get the freezer cold enough, and the fridge part too, but now in summer, the fridge part only gets down to about 9C, which is too high for the job. Have to go to propane to get the fridge part down to its proper range.Is there any way to increase the amount of cooling from the freezer part down to the fridge part? ( I have the eyebrow setting on "coldest" already) If there is, I would likely need to put it back the other way for when on propane so the fridge does not freeze, but one step at a time!Thanks.

Why is the 120 volt not repairable?Service manualOn 12 volt side make sure you are getting a good 12 volt power to the element not just to refer.

Hi BFL13,You would need to increase voltage to increase wattage.I know my fridge works ok on 12 volt--but ONLY when I'm plugged into shore power.

Enbethen,BFL13's electric heater is rusted into place. Hence it can't be replaced.

The 120v heater element rusted out and is rusted stuck in, so there is no way to replace it. One of the guys here described how he got his out, but I don't dare try what he did. Great risk to the whole stack part on mine! The control board 12v limit is 15.4 so I have to stay under that with the converter's adjustable voltage. There is some voltage drop in the board, but can't be helped. If I by-pass the board and go DC direct to the element I lose temp control for when it should cycle.If I put 15v direct to the 12v heater, leaving it also connected to the board,(to avoid the voltage drop in the board) and "regular" 12-14v from another DC source to the board as when on propane, the controls would not work---but maybe they would?I don't know if the terminals for the 12v element on the board, when seeing the 12v would "back feed" the board, same as if the board were getting power from its regular 12v inputs.What does the slider thing on the fins in the fridge do? ISTR you can play with that, but I don't know which way to move it, if that is the key.PT--good memory on my fridge situation! I don't follow why your 12v would work any better when you have shore power, unless you mean it works with 13.6v and not with 12.6v? I get no joy with 13.6 into the board. It needs 15.2 to get enough to the element.

Can you remove the 12 volt heater? A new 120 volt heater would fit. You can also just use a stainless hose clamp to clamp a new heater to the side of the boiler tube- pack insulation around it and it will work.

Fridge Temp Control Question | Good Sam Community

Chris_Bryant
Explorer II
Jul 29, 2019
One thing to keep in mind is that is basically a Norcold- Dometic built cooling units for Norcold for a while and in the deal they marketed the Unit with the server name.
wnjj
Explorer II
Jul 29, 2019
BFL13 wrote:
I think I got that this time! Have you a link to such a relay with illustrations for the terminals you describe--"common", N.O. pins, etc? Thanks!

I have ordered a 120v element but it is 325w instead of 300w in hopes I can make it work from the 120v output from the board. The specs for the 300 and 325 in amps and ohms are not much different.

The 120V option will be your best bet. If you still want to try the relay hack, Google for lighting relay diagrams since they’re basically doing something similar.

On automotive style relays, pin 85 and 86 are the coil , 30 is common and 87 is normally open. https://www.the12volt.com/relays/spdt-and-spst-automotive-relays.asp
BFL13
Explorer II
Jul 29, 2019
pianotuna wrote:
BFL13,

325 watts is what mine draws. I hope you will be pleased with the results.

The Dometic in my ride is a 6 cubic foot.

I could not find the 300w rated part for mine on Amazon, but figure this 325w rated part will be close enough. The rated 325w must vary in real life anyway depending on what the "120v" is at.

Doug, you are right, but it was worth it for me to do the 120v powered 12v trick. It worked ok in winter ambients where the fridge part was already almost in the proper temp range, but not now in summer. Can't get it down past 9C/48F and moving the thermistor did nothing as was predicted. the freezer part is cold enough though. I need to drill a hole in the freezer floor to let some cold down into the fridge! (Not!)
pianotuna
Nomad III
Jul 29, 2019
BFL13,

325 watts is what mine draws. I hope you will be pleased with the results.

The Dometic in my ride is a 6 cubic foot.
dougrainer
Nomad
Jul 29, 2019
pianotuna wrote:
34 amps @ nominally 12 volts. Mine operated just fine on a 35 amp PD converter with wizard. It was not a "planned" test, but rather happened by accident.

The alternator doesn't seem to power the fridge well at all in 12 volt mode.

dougrainer wrote:
2. Even if you have a 3 way refer, operating on 12 volts is ONLY for when the unit is in Transit and your Chassis engine Alternator is supplying the needed voltage/amps to power the 12 volt element. It is NOT designed to operate on a Power Converter, as it takes a lot of power to run that 12 volt element.

I should have clarified. 4 Cubic Foot and smaller RV refers will usually operate fine on 12 volts. 6CF and larger are NOT designed to run on 12 volts unless the Truck Alternator is engaged. 6 CF and larger, the 12 volt element is a MAINTAINER, not a cooling mode Heat element. Using a Inverter/Charger or a Power Converter to run a 6CF and larger on 12 volts is foolish and a detriment to a Power Converter. Why put the strain on those chargers when you can operate on 120 or LP? Doug
BFL13
Explorer II
Jul 28, 2019
wnjj wrote:
BFL13 wrote:
wnjj wrote:
BFL13 wrote:
I don't know if the terminals for the 12v element on the board, when seeing the 12v would "back feed" the board, same as if the board were getting power from its regular 12v inputs.

Yes, it would likely back feed into your whole RV 12V system. If you do want to go this route, buy a 12V relay and use the wires heading to the element to power the coil and then use whatever voltage the 12V element can take through the switches terminals to the element.

Still not clear on this. You have the relay being operated by the temp control switching the 12v element terminals? So you still need regular 12v into the board at its 12v input terminals.

Now the 16 or whatever voltage supplied externally to the element is being switched by the relay.

How do you get say 13v to the relay from the board's 12v element supply terminals, while the relay is switching say 16v? Two different voltages. I don't understand how this relay works so it can do that.

Basically, the relay coil “replaces” the heating element as far as the control board is concerned. Instead of switching the element on, it activates the relay coil. Then the control board can continue to operate at 12V. The heating element is connected from a separate supply (e.g. 15V) through the relay common and N.O. pins to the element. Connect the supply to the “common” terminal on the relay and the element to the NO terminal, with the other side of the element grounded. If you figure out which is already ground, you can just leave the element grounded at the control board connection and add the coil ground to it.

I think I got that this time! Have you a link to such a relay with illustrations for the terminals you describe--"common", N.O. pins, etc? Thanks!

I have ordered a 120v element but it is 325w instead of 300w in hopes I can make it work from the 120v output from the board. The specs for the 300 and 325 in amps and ohms are not much different.
wnjj
Explorer II
Jul 28, 2019
BFL13 wrote:
wnjj wrote:
BFL13 wrote:
I don't know if the terminals for the 12v element on the board, when seeing the 12v would "back feed" the board, same as if the board were getting power from its regular 12v inputs.

Yes, it would likely back feed into your whole RV 12V system. If you do want to go this route, buy a 12V relay and use the wires heading to the element to power the coil and then use whatever voltage the 12V element can take through the switches terminals to the element.

Still not clear on this. You have the relay being operated by the temp control switching the 12v element terminals? So you still need regular 12v into the board at its 12v input terminals.

Now the 16 or whatever voltage supplied externally to the element is being switched by the relay.

How do you get say 13v to the relay from the board's 12v element supply terminals, while the relay is switching say 16v? Two different voltages. I don't understand how this relay works so it can do that.

Basically, the relay coil “replaces” the heating element as far as the control board is concerned. Instead of switching the element on, it activates the relay coil. Then the control board can continue to operate at 12V. The heating element is connected from a separate supply (e.g. 15V) through the relay common and N.O. pins to the element. Connect the supply to the “common” terminal on the relay and the element to the NO terminal, with the other side of the element grounded. If you figure out which is already ground, you can just leave the element grounded at the control board connection and add the coil ground to it.
BFL13
Explorer II
Jul 28, 2019
Chris Bryant wrote:
Boy, that does look smaller diameter...

EDIT --It might just look thinner by being behind the other one, hard to tell. 300w vs 225w--would the 300 be fatter?

This is the 12v one:

https://www.ebay.ca/itm/Refrigerator-Heating-Element-Dometic-2943467-007-Direct-2-U-SKU-2910/163722694417?hash=item261ea20f11:g:huIAAOSwBQVc-Ugt&vxp=mtr

Says it is 225w and 18.75 volts. Howinheck can it get 18.75 volts? EDIT--the table linked below shows that the 18.75 is amps, not volts as shown on the eBay link.

The 120v element is part # 2943469.003 at 300w. Listed here, but can't find one right off using that number. They do change the numbers. Lots of those 325w ones, but don't know if I can use one. It would be clamped onto the pipe, not sitting in its sleeve.

http://techsupport.pdxrvwholesale.com/wp-content/uploads/2019/01/Dometic-Refrigerator-Technical-Data-Chart.pdf
Chris_Bryant
Explorer II
Jul 28, 2019
Boy, that does look smaller diameter...
grizzzman
Explorer
Jul 28, 2019
You could use a boost converter to feed the 16 volt side. Or a buck converter for to the board power.

Forum Discussion

Fridge Temp Control Question

About Technical Issues

Related Content

ARP Control for fridge

more electric control panel questions

outdoor kitchen fridge question

dumb question about my fridge

Residential Fridge