Can I jump fridge gas valve for TS purposes?

Hook the 120 volt element to power. Unless that has been updated, I believe it used the old Weber valve which doesn’t work like a normal valve.
That said, if it is still available Dometic has a conversion kit with new gas valve, burner and circuit board.

In gas mode, first clean the orifice (I soak it in mineral spirits, and blow through to get it to squirt like a water pistol) but the pros here have other ways). Your solenoid might be ok, don't know until confirmed orifice is clean. Check all wire connections to the solenoid too.

Bang on the flue above the burner slots to shake loose any soot flakes and clean out all soot that might have gone down the slots

On my 1991 3-way Dometic, the AC heater element was rusted out broken so no good. You can check for 120 at its blade terminals on the side of the board. There is a 120v fuse on the board itself (5a on mine) and a 12v fuse (3a on mine) to check.

Like Chris suggests
Direct connect the 120v heating element, with a cheater cord
If it cools fridge is good, replace board
Don't mess around with trying to power the gas valve

Don't know if THIS is the manual you have....LOTS of really good info on the RM3604/3804 fridge

Diagnostic Service Manual

FWIW, the way that valve works is it is powered during trial for ignition, once the flame is ignited, power is dropped and the thermocouple holds the valve open. Shutting it off, the board send ~80 volts dc reverse polarity.

A common failure is if you hear the valve cycling a lot, it is due to oxidation on the thermocouple. When the board stops powering the valve, the gas shuts off and the board kicks in again. To fix, Unscrew it from the gas valve and polish the end with a pencil eraser, then snug it down firm, but don’t crush the insulating piece.
Those valves hardly ever fail, but I have a few of them.

MrWizard wrote:
Like Chris suggests
Direct connect the 120v heating element, with a cheater cord
If it cools fridge is good, replace board
Don't mess around with trying to power the gas valve

+1 on this it is the simplest way to check the unit.

Old-Biscuit, yes, that is the same manual I've been working from, along with another from Dometic that I think it for an older model 3 way in the same series, but has a handy flow chart for troubleshooting purposes.

I had gone to "it's a board issue" since I wasn't getting any voltage on the AC element output, was getting low voltage on the DC output, and hearing the gas valve cycling. That valve is cycling at the same rate that the igniter is firing, but it doesn't appear to ever be flowing any gas through. When the gas valve is cycling, it's doing so with very loud clicks, which I don't know if that's normal or not. It's loud enough that I can hear it inside the camper as well.

I also found 3 wires on the 6 pin connector had melted insulation, as well as the 2 pin wiring harness going to the gas valve. I've since repaired those wires by cutting out the damaged sections and splicing in new wires.

I didn't see any obvious fuses on the control board, though I didn't inspect it throughly either. There may well be SMD fuses that have failed. As a point of reference, I'm a low voltage/electronics tech by trade, so I have a tendency to dig into this stuff deeper than most people probably would, lol.

I'll take a closer look at the board tonight, and pull the gas bits for further inspection and cleaning. Thanks all!

On mine you have to unscrew the Power Supply (the board) from the back of the fridge, take the cover off, then pry the board out of its "tray" to see the components.

The 120v fuse is by the bottom side terminals where the 120v cord goes on.

The DC fuse is at the other end (the higher end when all installed)

DC voltage drop on mine was big. I have the long wire from battery to the terminal block behind the fridge, losing 0.5v at 9 amps.

But then the 12v supply wires go to the side terminals of the board, through the board to the output 12v terminals at the side of the board . You get another half volt or so loss there. But the spec on mine says DC can be from 15.4 to 10v, so "low" can still work.

IM not expert O , since you are getting ignition and can hear the solenoid, your board is ok, and you just need gas from the orifice or to unblock the burner where soot may be in the slots.

You might have the 120v fuse blown on the board, but first confirm you have 120 at the receptacle the cord goes to. If that is dead, try an extension cord from a known live receptacle. You can also check the cord itself by plugging into a good source and meter the end that goes on the board. If fridge then works on 120, you can solve the receptacle problem.

When I was speaking of the DC voltage, I meant the voltage FROM the control board, TO the DC relay. That's where I was measuring the 5VDC, and also getting relay chatter. The voltage going to the fridge connector is 13.6VDC, coming from the onboard converter.

I pulled the control board completely out of the fridge a few minutes ago, and there are definitely burned components on it, that I haven't yet identified. Appears to be either a resistor or diode, immediately under the 6 pin connector. One of the large capacitors may also have gone dry, based on the cracks in the insulation.

I jumped the AC heating element, and if the cooling unit passes, I'll pull components off the board for further checks. When I first applied power, I got a pretty loud gurgling noise from the boiler, and my heart sank, thinking that I had a leaky cooling unit too. But after about 5 mins, it quieted down significantly, and now it's going in cycles of quiet and gurgling....I figure I'll let it run like this for a few hours to see if I notice any cooling inside before making a terminal diagnosis.

The board is a mess, unlike my earlier thought!

The damage seems to include the connection to the eyebrow control board, so no thermostat control for the 120v heater. I suppose you can tell if it heats up anyway. You can feel it hot at the flue when it is.

I do not know if all the outputs from the board are specified the same voltage. Cannot say if 5v for that one is right or wrong. Only have the input spec.