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Old 07-12-2016, 01:02 AM   #1
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Dometic DMR702 Boondocking

Taking your newer Dometic refrigerator boondocking?
Want to drop 1/2 an amp of constant 12V power?
Don't care about some potential condensation?

Here is how you fix this problem

First there are 2 different heaters in your Dometic DMR702:
1. The LAC "Low Ambient Control" heater - this one only runs when the outside air temperature is cold enough. It is possible that the fridge compartment can run too cold and the freezer to hot under some conditions. So they fix it by introducing a bit of a heat source into the fridge section. This heat source is a 18 ohm resistor burning off almost an AMP of 12V power.
2. The real crime though is the condensation control heat loop that runs ALL the time and burns off 1/2 AMP of 12V power. Just to prevent condensation from occurring between the two doors.

Some folks remove a fuse to disable these but you can do MUCH better, like disable the heater but still have lights in your fridge.

Here is the LED light and heater connection PC board as it comes out of the top of the fridge section:
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And this is the top side of the PC board after removing from the plastic housing:
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Note the 2 pin/wire connection - this is the heat loop connection and the simplest thing you can do is leave this disconnected. This will disable the heat loop but leave the LAC function enabled. Since the LAC is thermostatically controlled it will not be a factor in many cases. BTW that large beige ceramic block is the LAC heater.

Now if you want to get fancy you will need to add a couple of switches here. I used some PC board mount slide switches, one for the LAC and another for the heat loop. This picture shows the top side of the PC board modified for both of these switches. The LAC switch (in the middle of the picture) is inline with the PC board traces for the LAC and one has been cut between the switch mounting pins. The heater loop switch is on the right side and all you see is a couple wires connected to the switch pins. This switch was mounted in an otherwise open area of the PC board with no traces. Note that the switch is a DPST and both poles have been connected to the wires.

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This picture shows the same switch modifications but from the bottom side of the PC board. Not much to see on the LAC switch since it is using the traces on the other side of the board. But here you can see where the wires hook up for the heater loop: one to the terminal block post and the other to the 12V input on the 4 wire terminal block. The PC board trace that normally connects these two terminal block pins has been cut.

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And this last picture shows the PC board mounted back into the modified plastic housing. The housing has been cut around the switches to allow them to sit flush with the bottom of the housing. When mounted back in the fridge you will not even see the switches unless you look. I recommend labelling which switch is which and which direction OFF/ON are in.

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Turn off that head loop switch and you can save 12 AH per day while boondocking. Keep those batteries charged and the beer cold my friends
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Old 07-12-2016, 06:17 AM   #2
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Dometic DMR702 Boondocking

Thanks for the great documentation.
I just cut the wire by the fridge light switch and done.
The lac is not common on most fridges.

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Old 07-12-2016, 06:34 AM   #3
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Ok I replaced the stupid blue light board with white light board and the new board no longer beige ceramic block. So is this mod still uefull? Later RJD
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Old 07-12-2016, 06:45 AM   #4
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Like I said, I just cut the wire, less then two minutes and it can be hooked back up.





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Old 07-12-2016, 08:12 AM   #5
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Any concerns of the condensation caused by disconnecting the condensation heat loop getting behind and into the eyebrow board?
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Old 07-12-2016, 09:27 AM   #6
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Quote:
Originally Posted by aceinspp View Post
Ok I replaced the stupid blue light board with white light board and the new board no longer beige ceramic block. So is this mod still uefull? Later RJD
Your board has mostly the same circuitry: all of the PC board traces are there for the LAC resistor but they have not "loaded" that component. So you can skip the LAC switch.

The heater loop switch is still applicable. I would study the PC board traces carefully to make sure the switch mount area is still open on your version of the PC board. You do have a bit of extra circuitry as evidenced by the extra component on yours.
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Old 07-12-2016, 09:31 AM   #7
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Thanks for the great documentation.
I just cut the wire by the fridge light switch and done.
The lac is not common on most fridges.
Indeed your version of the modification works for older Dometic fridges. But for those of us with newer hardware things have changed, thus my writeup.

Note that the LAC may be more common than you think: they used to use the incandescent light bulb as the LAC heater. That trick does not work so well with cool running LEDs as the light source.
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Old 07-12-2016, 10:28 AM   #8
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Dometic DMR702 Boondocking

Quote:
Originally Posted by stevejahr View Post
Indeed your version of the modification works for older Dometic fridges. But for those of us with newer hardware things have changed, thus my writeup.



Note that the LAC may be more common than you think: they used to use the incandescent light bulb as the LAC heater. That trick does not work so well with cool running LEDs as the light source.


My fridge is brand new, less then a year old in my new camper.



All the campers I've seen, I've yet to see one outfitted with lac.




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Old 05-21-2017, 11:32 AM   #9
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Nice mod. Another option is to disconnect (or install a switch) on the ground side of the light/door heater circuit. In the rear access panel 4 black wires are joined together on a screw terminal. One is the ground feed from 12v, it's a very short jumper. One goes into the control board box. The other two go up into the fridge compartment above. One of those is for the fan above. The other one is for the interior light and the door heater tape. Unscrew (or switch) that one and the door heater and light are offline. But, it leaves the LAC heater intact because the LAC has a separate ground connection on the circuit board.
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Old 05-21-2017, 12:03 PM   #10
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Sad thing is, Domestic used to include a switch for the door heater on the control panel. They saved a few cents and now boondockers have to improvise.
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