Dometic fridge will not work on AC

[akerrairstreamer]

I have a Dometic RM2551 made in 2010.  Its a 2-way.

I've spent the last two days researching this and reading every post, but I'm not having any luck.  Much as I hate to start another thread, here goes.

When I turn the fridge on it immediately calls for gas, and the check light will eventually turn on.  I can hear the pilot light click.  It works fine on gas, but I'd rather use electric or have electric as an option at least.

I've got AC at the outlet, and I've tested and get AC across the fuse.  I wasn't getting any power at the electric heating element pins on the control board, it just seems to never detect that it has AC even though it does.  Ohms across the heating element are within spec as well.

After going through all the troubleshooting I finally decided it HAD to be the control board.  I just picked up a new one and installed it today, and SAME PROBLEM.

The only thing I can think of is something with the upper mustache board, but I don't know how to tell - and its pretty basic and I can't see what would be wrong there.  Its clearly in 'auto' mode and not the 'gas' mode, and the 'auto' light goes on and off when I toggle the button so I think that means the control board received the signal and has turned on/off the auto light.

Wiring all checks out, no shorts, etc.  Its very clean, its a 2012 camper new to me but always stored and kept clean, but I don't know the full history and the previous owner I believe didn't use shore power often.

Sure would appreciate any expert help.  If its got 110vac AND good 12v (micro works, power meter shows great volts and amps for both 12 and 110, etc) I'm just at a loss.

 

[donn]

Did you buy a Dometic or dinosauer board?
Im far from an expert, but 120VAC as I understand it the 120V goes to the control board, is switched by a relay on the board and then feeds to the heater. If you cant get 120V out of the board, and you have verified the fuses on the board are good, then its pretty obvious a bad board. I dont see any reason the eyebrow board does anything but switch as selected.  You might search out a wiring diagram online to prove out my outline.

 

[Arch Hoagland]

OP said : "I've tested and get AC across the fuse. " 

If a probe is on one end and the other probe is on the other side of the fuse and you read 110 volts AC then the fuse is bad. 

A fuse is a dead short and no voltage can be read across it.

 

[akerrairstreamer]

Thanks for the feedback.

To clarify, I bought a replacement board brand new from a Dometic repair shop.  Its a newer revision of the board but we tripple checked that it is correct for my model and revision of fridge.

When testing AC I tested with my ground against the plate on the fridge where the AC ground is terminated.  With my positive probe I get 110v on both sides of the fuse while leaving my negative probe on that ground terminal.  I'm not getting 110v with one probe on one side of the fuse and another on the other, I agree that'd mean something seriously wrong, but that isn't the case.  The fuses are all good.

I've read the wiring diagram numerous times, and replacing the board was my last resort.  I don't think it could be the eyebrow board either, but I'm at a loss.  Two boards, same behavior.  I have to believe the new one at least, from the factory, was good!

If the fridge starts up, properly calls for cooling, and it decides to start the gas - what else other than the lack of detected AC would cause that?  And I'm clearly getting AC, I've checked the plug (obviously), at the fuse (which confirms I'm getting power)... what else is there in that decision making process to pick gas over electric?  The heating element ohms reading is correct, but even if it wasn't shouldn't I see voltage on its terminals at some point before the fridge decides to light the gas?  I can test again unplugging the heating element and just watching my meter at the electric heating element terminals for voltage, I'm 99% sure I did that properly the last time and never got anything at all before the gas started to light.

PS thanks for helping, getting past that image varification takes me 20 minutes each time, my eyes are bleeding.

 

[Scott 3]

Following...  same issue Norcold

 

[donn]

On the front panel the switch should be gas only, electric only or auto.  What do you have it set to?

 

[akerrairstreamer]

The dometic only has "auto" and "gas only" (a 3-way would have a DC option, but mine is a 2-way).  The "auto" is *supposed* to prefer electric and use gas as a backup, but in my case it just always uses gas, which is the issue.

 

[Gary RV_Wizard]

Going back to basics...
If the circuit board cannot detect 10vac power, it won't close the relay to power the electric heater and will activate the LP gas mode instead.  That is exactly what is happening, so we need to figure out why.  A failing main circuit board was a fair guess in this case, but no luck there.  I don't think the eyebrow board could cause a failure to detect AC, but do not know that for sure.

The only other things I can think of is that the AC voltage that is present somehow does not meet the test criteria, e.g. low of high voltage, not 60 Hz frequency, poor neutral wire connection, etc.  I'd investigate the quality of the power as seen at the fuse and make sure the voltage I was detecting was measured against the circuit boards neutral reference point. When you tested the voltage, you probably bypassed the circuit board neutral reference and connected your meter direct to a known good neutral point.

 

[WILDEBILL308]

Have you checked the 12 volt side? The board controls the 120V side but runs on 12V. Look for a bad 12V fuze or lack of 12V power.
Bill

 

[Gary RV_Wizard]

If he didn't have 12v, it would even light up the eyebrow panel, let alone run in LP gas mode.

 

[akerrairstreamer]

Thanks Gary, I've just tested the new board which is still installed.  I've got a good 112v reading with the ground at several locations on the board - the screw that attaches it to the frame, another spot unused on my camper but set up for another grounding screw, and at the ground pin.  I'm testing the positive side still on either side of the fuse just to be 100% sure.  Thats all about my current multimeter can do as far as testing.  The camper is in my driveway using a 30am-20am adapter, but its a known good plug that I've used before and powers other things just fine (of course nature could have changed things, mice, water, etc - but I normally have a small fountain pump connected and it has been and still is happy to be plugged in there).  I know people have had all sorts of power issues at campgrounds, but my house seems pretty consistent.

Thats why I was wondering if anyone had any insight in to the decision making process of the board.  I'd expect that if it found 110v, even if it was dirty, it'd prefer that source.  I wonder if anyone happens to know if it checks any other input sources only when it wants AC, and grasping at straws but there is a thermister (or something like that) at the top of my fridge on the fins behind my freezer, a fan is also attached there (its DC and is currently running).  Does it check resistance for any of that ONLY on AC and not when on gas?  Or is the ONLY thing it looks for in that decision process between gas an AC the presence of AC?

I'm off camping first thing in the morning, so maybe it'll magically be better tomorrow with a different power source.  I'll report back, but I'm not very hopeful.  With 60# of LP though I'm not too worried.

 

[Henry J Fate]

I am fairly certain that the new control board and the original control board do not decide what mode to run or at least not within their circuitry. I am fairly certain that the command to run the fridge in a certain mode is sent to the control board from the eyebrow board. The two boards work together. It maybe time to replace that brow board. Nothing is for certain but if everything checks out and the control board is new, it is looking like the eyebrow board.

I would suggest to use one of the Dometic technical support numbers to try and get some factory help for your next step.

https://www.dometic.com/en-us/us/contact-us

 

[Gary RV_Wizard]

I am fairly certain that the new control board and the original control board do not decide what mode to run or at least not within their circuitry. I am fairly certain that the command to run the fridge in a certain mode is sent to the control board from the eyebrow board.

LOL, Henry, I'm equally certain that is NOT the case when the mode is set to AUTO.  The main circuit board selects AC mode if a nominal 120v is present at the board but automatically reverts to LP Gas mode if not. There is no way the eyebrow board can determine that.  The eyebrow board sends the switch state to the main board, either Auto or Gas and the main board handles it from that point on.

There is no AC mode on the RM2551 - the only choices are AUTO and GAS.

 

[Koodog]

Did you check your AC across the wires and not ground?(frame, screw or other metal surface)
You may be missing your neutral.

 

[Rob&Deryl]

Did you check your AC across the wires and not ground?(frame, screw or other metal surface)
You may be missing your neutral.

+1

 

[Gary RV_Wizard]

Did you check your AC across the wires and not ground?

+2

 

[Henry J Fate]

LOL, Henry, I'm equally certain that is NOT the case when the mode is set to AUTO.  The main circuit board selects AC mode if a nominal 120v is present at the board but automatically reverts to LP Gas mode if not. There is no way the eyebrow board can determine that.  The eyebrow board sends the switch state to the main board, either Auto or Gas and the main board handles it from that point on.

There is no AC mode on the RM2551 - the only choices are AUTO and GAS.

You may be correct but when I say mode, in this case it is auto, gas or off. If the upper control board is not functioning properly and keeps telling the lower control board to use the gas mode, gas mode it will be and is that not what the symptom is?  It dosent matter what the upper board is indicating. That may not be what it is doing. The upper board tells the control board what to do in all cases either auto or gas or off. My guess is that the upper board is malfunctioning and keeps applying the gas mode. I dont quite see how you could eliminate the upper board as being the problem after 2 lower boards producing the same malfunction, It is definitely on the list of possibilities.

Another suspicion would be the inter wiring between the upper board and the lower board. Could be a bad wire or connection somewhere in that communication link.

If you can get at the upper board, reset the connector to it and inspect it while it is disconnected. Both the connector and mate on the upper board. IF you can follow the cable from the upper board to the lower board, have a good look at the wires to be sure they are in good order.

 

[gentlewind]

I have a Dometic RM2551 made in 2010. Its a 2-way.

I've spent the last two days researching this and reading every post, but I'm not having any luck. Much as I hate to start another thread, here goes.

When I turn the fridge on it immediately calls for gas, and the check light will eventually turn on. I can hear the pilot light click. It works fine on gas, but I'd rather use electric or have electric as an option at least.

I've got AC at the outlet, and I've tested and get AC across the fuse. I wasn't getting any power at the electric heating element pins on the control board, it just seems to never detect that it has AC even though it does. Ohms across the heating element are within spec as well.

After going through all the troubleshooting I finally decided it HAD to be the control board. I just picked up a new one and installed it today, and SAME PROBLEM.

The only thing I can think of is something with the upper mustache board, but I don't know how to tell - and its pretty basic and I can't see what would be wrong there. Its clearly in 'auto' mode and not the 'gas' mode, and the 'auto' light goes on and off when I toggle the button so I think that means the control board received the signal and has turned on/off the auto light.

Wiring all checks out, no shorts, etc. Its very clean, its a 2012 camper new to me but always stored and kept clean, but I don't know the full history and the previous owner I believe didn't use shore power often.

Sure would appreciate any expert help. If its got 110vac AND good 12v (micro works, power meter shows great volts and amps for both 12 and 110, etc) I'm just at a loss.

Hello, I have exactly the same problems with my 2663. Did you ever find a fix or what the problem was? I have done everything that you have, including the new circuit board. My next try would be the eyebrow board. Any updates with you? Thanks!

 

[Scott 3]

A new control board fixed my issue.

 

[Arch Hoagland]

Thanks for the update, glad you got it going.