Dometic fridge works only on LP for a couple of months

[hydrocynus]

Hello all.,

I have a DM2852RBX (dometic brand) for a couple of years and it started acting about two years ago by cooling with LP only. It is a two way fridge that works on AC and LP only. I took the manual and tested all the components. The heating AC component reads 44 ohms which is spot on, the board is under voltage and receives the adequate DC and AC. Both fuses are good. When I remove the thermistor to test the board the fridge still works on LP only. I cannot get it to switch to AC. The AC heating element does not get any current/voltage.

Based on my testings, I ordered a refurbished board from Amazon (Dometic (3316348.900)) but after installation, the fridge still switches to LP (although it is on AUTO).

So, I suspect my heating element although the resistance tests correctly. Any idea before I order a new heating element? The reason I am doing all the diagnostics myself (the unit still under warranty) is that the cost of a visit by a specialist is more than just replace the parts (if I had an ammonia leak, that would be different).

Thanks for helping.

Serge

[hydrocynus]

Chris Bryant wrote:
That is the correct board if the original had the integrated ignition module. Does the AUTO light come on but it stays on LP or does the AUTO light not come on?
With the switch in the auto position, check for 12 volts between the red (-) and black (+) on the 6 position plug on the lower board.

Chris, I was reading again your post. I am not sure what is needed to be tested here:
"With the switch in the auto position, check for 12 volts between the red (-) and black (+) on the 6 position plug on the lower board."

Can you please clarify? thanks a bunch

[hydrocynus]

I received the part this morning. I unhooked the AC and DC power, even pulled out the fuse just to make sure. I turned off the display panel.

I installed the board, connected everything, tested everything before I applied power. Unfortunately, the fridge still switched to LP cooling on AUTO (solid LED lit).

I got an extension cord, plugged the fridge into clean AC power from the main AC outlet getting to the Home, still I am getting LP cooling.

I then additionally connected the fridge to a brand new fully charged battery, and still LP cooling.

Of course, fuses were tested (including their mounting brackets), heating element tested for resistance (44 ohms), thermistor tested as the manual indicates (but that is not really an issue here as I can either let it plugged in or unplugged to get the fridge to cool and I still get the LP cooling), heating element connected to the the AC supply to bypass the board's switch and it heats up good.

So, the only thing I have not tested is the display control board. I have the old one from the fridge I replaced when I bought this fridge that causes me issues. It is in the storage, so I will get it and plug it in to see what happens.

Meanwhile, I ordered a digital temperature controller to fully bypass the board and control the AC power getting to the heating element. At least, I will be able to control the temp inside the fridge better than rising the thermistor up and down.

Cost is only $20 bucks for the controller and all the parts.

If you have any ideas (looks like I have tested everything), let me know.

[hydrocynus]

BTW, when pulled out of the unit, the heating element works when connected on AC. Waiting for my new board to arrive. I highly suspect this was the replacement board as it was from amazon warehouse deals (ie. return from customers and not a refurbished item). I will let you know. I think I have done all the testings needed to be done on both boards.

If the error persists, I will just hack the fridge and control the heating element with a AC freezer temperature controler (about $50) and be done with it.

Cheers to all.

[hydrocynus]

Chris Bryant wrote:
That is the correct board if the original had the integrated ignition module. Does the AUTO light come on but it stays on LP or does the AUTO light not come on?
With the switch in the auto position, check for 12 volts between the red (-) and black (+) on the 6 position plug on the lower board.

The auto light is solid on AUTO, the LP light does not lit unless I switch the fridge to LP only. I tested the thermostat which works as well as the display control board.

[Chris_Bryant]

That is the correct board if the original had the integrated ignition module. Does the AUTO light come on but it stays on LP or does the AUTO light not come on?
With the switch in the auto position, check for 12 volts between the red (-) and black (+) on the 6 position plug on the lower board.

[hydrocynus]

So, FYI, I have been using the Dometic diagnostic manual to conduct my test. I read it again today and this is what it states for the AC mode:

Test upper control board and harness between upper and lower before testing lower for proper AC operation. Check that incoming AC voltage is present at terminals J5 (black) and J6 (white) on the circuit board. With unit on
AC operation, check for voltage at the heating element connection terminals J7 and J8 on the circuit board. If no voltage is present, check the 5 amp AC, 3 amp DC fuses, wiring harness and upper control. If AC volts are present at J5 and J6 and no voltage on J7 and J8 the AC voltage detection circuit is damaged and the control board will need to be changed.

J5 and J6 had the correct voltage but nothing on J7 and J8 when the unit is on AUTO. I cannot get the control board to be on AC only since I only have AUTO and LP. How do I force the unit to be in AC mode only?

Again, this occurs with a refurbished board that I changed after I suspected the original board was faulty.

Additionally, it just occurred to me that I forgot to mentioned that I replaced the board with a slightly different board: Dometic (3316348.900) Power Module Board which only has a 5amp fuse instead of 3amp and 5amp fuses on my original board. I was told by the vendor on amazon that this was the correct replacement board for my model.

Could this be the issue?

[hydrocynus]

j.p.f. wrote:
sounds like you tested everything except the ac/gas switch on the fridge?

Correct, I did not test the control board on top of the fridge.

[hydrocynus]

Chris Bryant wrote:
When you are checking points on the board for 120 volt power, are you actually testing between the board neutral and hot, or are you just grounding the meter and testing for power? Also are you testing it under load- i.e., turned on set on AUTO ?

I have tested it by removing the rubber caps of the plugs of the AC input and the meter reads the right voltage. I also unplugged the AC plug and plugged it onto the main power input to the construction site. The fridge still switches to LP automatically (under the AUTO mode).

This is a great forum guys! Thanks for your help!

[hydrocynus]

I have to get the person come over to the 5th wheel trailer as I do not have any means to move it. It is on our construction site until the house is built.

In any case, the fridge seems to be out of warranty (although it is pretty bad that the manuals did not get reprinted with the correct warranty info), so it looks like I am not doing anything wrong.

The fridge cools on propane so it is OK for me if I cannot get it to work on AC (although I could just bypass the board and make it run on AC using my own board, like I have done to transform chest freezers into a solar powered fridge).

[Chris_Bryant]

When you are checking points on the board for 120 volt power, are you actually testing between the board neutral and hot, or are you just grounding the meter and testing for power? Also are you testing it under load- i.e., turned on set on AUTO ?

[j_p_f_]

sounds like you tested everything except the ac/gas switch on the fridge?

[dougrainer]

hydrocynus wrote:
BTW. My manual states 3 year exclusive warranty.

I know, but the manual is wrong. They never reprinted the new warranty terms. Still YOU modify a under warranty product with aftermarket parts and you VOID the warranty. If you brought that unit to my shop and I see the Dino board, you would then be PAYING me to fix it as Dometic will also NOT pay to fix. Why did you not just take it to a Dometic Service Center? Doug

[hydrocynus]

BTW. My manual states 3 year exclusive warranty.

[hydrocynus]

Sorry about the discrepancy. The title says 2 months but my post states 2 year. The correct time is 2 months.

The unit is correctly set to auto. It used to cool on ac when set on auto. To test the unit i disconnected the temperature sensor. It then cools on LP but not AC.