Dometic RM3601 Fridge works on AC but only sometimes on propane

I have a 1989 Lance truck camper with the original Dometic RM3601 reefer.

The unit will always run perfectly on AC. It usually runs fine on propane, but sometimes it will not attempt to light. When this failure happens, I can run the reefer on AC for a while (maybe half an hour) and then the propane always fires off and works fine.

When it doesn't fire off, I can not hear or see the propane valve click or the igniter spark.

I'm assuming the wiring and various circuits must be hooked up correctly or it wouldn't work at all?????

Might there be some component (igniter, valve, etc) that doesn't always work at, say, 12.8V but works nicely at 13.5V and above and, therefore, only works with a very, very well charged house battery?

Any thoughts or suggestions would be appreciated.

Are you making sure the unit is level

Yes, the camper and fridge are dead level.

"Level" won't stop it from igniting - it just may not get as cold as it should.

My best guess is a faulty control board, intermittently knocking out the LP igniter circuit.  The fridge uses 12v for control purposes even in AC mode, so the 12v and 120v wiring should be ok. That leaves the gas igniter circuit as the problem. Either the control panel ("eyebrow panel") isn't correctly signalling that LP gas mode is selected OR the main control board simply doesn't respond to LP mode every time.

For replacement boards.............

Be sure and read the Service Bulletin info at the top of the page.

https://www.dinosaurelectronics.com/Dom_boards.htm

According to their chart a RM 3601 uses a P246 Plus board

https://www.dinosaurelectronics.com/MICRO_P-246.htm

Here is the eyebrow board for the 3600 series.

https://www.dinosaurelectronics.com/RM35_36_38.htm

You have to buy from one of their dealers https://www.dinosaurelectronics.com/Online_Sales.htm

Charles

Thanks for the replies. I will try replacing the control boards, one at a time. Any guesses as to which one to try first?

I really appreciate the help!

Danl

OK. I replaced the control board with the Dinosaur board. No luck. Nothing changed.

But I was doing the diagnostics again with my VOM and checked the resistance across the coil of the solenoid valve again. Read 19 to 20 ohms, just like before. But, as I was pondering "what next" and continuing to hold the probes on the solenoid, the readings were all over the place; 19, 20, 87, 91 7, OL, 7, OL, 82, 19,18,20,19, 87, OL........etc. I can repeat this test with the same results. So maybe I need a new solenoid/valve assembly. Anyone have a lead on the correct part number and perhaps a source to buy from?

Thanks for all your help!

If the solenoid has external terminals, re-do the solder joints at the coil terminals.  You may have a bad connection where the internal wires connect to the terminals.

Thanks, Lou. I'll try that, I guess.

I checked again to be sure that the previous behavior has not changed with the new board and nothing has changed. If the LPG doesn't start, I plug into shore power, run the reefer for 20 minutes on shore power, and then the LPG always fires off. Very weird!! This time I checked the solenoid before I tried the reefer after it was running on shore power and it tested at 20 ohms and steady. Then the reefer fired off on LPG just fine!!!!

You mentioned that sometimes when placed in the gas mode that nothing happens. No spark no sound of the valve opening. You should be witnessing one or the other or both. If it does nothing, it sounds like the control board is not receiving the command.

Be sure that the gas valve is not opening. You should be able to smell gas in the service door. Be sure that no gas is being vented and the valve is not opening.

A bad ignitor is very typical however a bad ignitor/sensor will not prevent the flow of gas at start up.

You will have either a combo ignitor/sensor or an ignitor and a sensor. These components are responsible for igniting the gas and confirming a flame is present. This becomes a likely suspect if  gas is being vented. Make sure there is no gas.

If the gas mode produces no response at all, it becomes likely that the control voltage (12 volts) is not making its way to the control board or the gas mode command is not getting to the control board.

A freshly charged battery will offer about 12.6 volts. When you plug into shore power the voltage will be 13.5 - 14 or about.

Thanks for the input, Henry.

When the gas doesn't light, there is no click from the valve, no gas or gas smell, and no click or spark from the igniter.  So your thought about the "gas command" not being sent sounds right. I guess I can replace the eyebrow board on the fridge and see. Is there a way to manually fake a "gas command" on the main control board? If so, that would isolate the problem to the eyebrow board.

I still can't figure out why the gas always works if I first run on AC for 20 minutes or so. Any ideas?

Probably time to look at the brow board. There should be a connector to it. Many times the connections within connectors will become stagnant. Removing the connector and reconnecting it may solve a connector problem. Try that at the eyebrow board to see if anything changes and while you have that connector off, have a good look at things before reconnecting.

There is a way to jumper commands to the lower control board. That would require a review of the wiring diagram. It becomes a little tricky when you get into that sort of stuff. I would first try the connector reset.

I suspect that if you plug into external power without placing the fridge in the ac mode, you may still find the gas mode working. A logical guess would be that the increase in control voltage is having some effect on the control circuit.

You have a new lower control board. The new board has produced the same symptom as the old board. The symptom is that when in the gas mode, nothing happens. No spark, no gas, nothing but mysteriously it fires up after a short period of running in the ac mode.

The chances of two bad lower control boards is very low.

The valve issue that Lou mentioned would be a little more intriguing if you were getting a spark as those two circuits should be completely separate at start up, meaning that if the valve is bad, the control board should still produce a spark.

Since the gas mode works fine at times then it becomes likely a command issue. Something between the lower control board to the upper board. (eyebrow board)

Another thought....

I believe the 3601 has a delay built into the gas mode. This is dependent on the way the unit is wired.

The delay is applied when the fridge is in the 12 volt heating mode. The 12 volt heating mode is designed for when you are traveling which requires the ignition key to be in the ON position. If wired this way and with a 12 volt heating element, the fridge will automatically switch to the 12 volt heating element when the vehicle is turned on. To prevent an un safe condition when stopping for fuel or likewise, they built in a 25 minute timer which prevents the fridge from going into gas mode for 25 minutes. It will however turn on immediately in ac mode if you plug in during that 25 minute delay.

Do you have a manual for your fridge?

https://www.google.com/url?sa=t&source=web&rct=j&url=https://rvrefrigeratorrepair.com/wp-content/uploads/2016/07/Dometic-Service-AES.pdf&ved=2ahUKEwjuxcb5p8rqAhVqQt8KHem-A4sQFjABegQIARAC&usg=AOvVaw21txHkvh1iHrDYulD_g4nU

This link should help. I could not find the owners manual for the 3601

Thanks for all the help and suggestions, Henry. I'm going to uninstall, clean, and reinstall the eyebrow board today. Hopefully, I can find something.

I do have the manuals for reefer. Thanks for the link, though. It's good to have a digital copy.

Good thought on the increased voltage from shore power. I had stumbled on that earlier. However, if I plug into shore power and then try the gas option it doesn't work, even if I wait an hour. It seems that I have to actually run the reefer on AC for about 20 minutes and then the gas option works. Weird!

Danl

Hopefully the brow board produces an answer. That 20 minute wait for the gas mode to work is awfully similar to the gas mode delay when traveling. I do not know how they designed that delay or where it physically is delaying the gas mode.

Another thought, was the fridge running fine and then started the current symptoms? Maybe a history lesson might produce another clue. Good luck with the brow board.

Good news, bad news.

Good news: After speaking with a tech at Dinosaur Electronics, and doing the metering of components again, I am now sure  that I have a bad, intermittent igniter.

Bad news: Due to my previous poor metering abilities, I now have a brand new expensive, but unnecessary, control board.

Could be worse. The new igniter will be here Wednesday. I'll update then.

Again, thanks for all the help.

Danl

So the gas valve was opening and venting gas but not igniting?

No. The Dometic manual is not crystal clear, but the tech spelled it out much more clearly. When the LPG option is chosen, the control board first sends 12v to the igniter. There is a mechanism for the control board to detect whether or not a spark is actually being produced. If a spark is detected, then, and only then, the control board sends 12v to the solenoid valve to apply LPG to the now sparking igniter.

So, sometimes my igniter module would not respond to the 12v, therefore no sparking sound and as a result no clicking of gas valve. I misinterpreted the manual to say that both things happen at once.

Hopefully that will solve the problem.