Dometic fridge won't run on gas

[Tel7]

We have a 2010 Bailey Pegasus 554 with a Dometic RM 8550 fridge (according to the sticker behind the vege tray).

After much effort and help from several of you, I solved a problem with a stuck corroded igniter battery, thank you, and I was able to start and use the fridge successfully.

However, in our next visit to the caravan (now), I can't start it.

The gas is on at the tank and is getting to other appliances, (and to the fridge I expect, based on the flame starting sound - see below).
All 4 caravan gas isolator switches are on.
I turn the fridge mode to gas.
I push in the temperature (thermostat?) knob in and turn it at least 75% way around and hold it in.
I then press and hold the igniter button in, and I can hear it clicking several times a second. I promptly hear it light up.
I release the igniter button (at that time or even 5 secs later), but continue to hold the temperature knob in for 15 or even 30 secs.
The needle doesn't start moving towards the green, as it did in our last visit, but I don't know what's changed. I release the temperature knob, and try again, but alas, to no avail.

Anyone had this problem before?
Any suggestions?

Edit: The manuals are here, but I'm not yet convinced any of the troubleshooting suggestions there are relevant to my situation.

Thanks.
Terry
NZland

 

[Jcloughie]

Possibly a blocked jet.

When working, you will hear the flame light.

John

 

[Tel7]

Thanks John,, but I already think I hear it light.

"I then press and hold the igniter button in, and I can hear it clicking several times a second. I promptly hear it light up."

It doesn't light up on every attempt though. If I leave it a while it seems to light again.

Still sound like a blocked jet? If so, how many jets are there and how to get to them and how to unblock them?

Thanks.
Terry

 

[Jcloughie]

Thanks John,, but I already think I hear it light.

"I then press and hold the igniter button in, and I can hear it clicking several times a second. I promptly hear it light up."

It doesn't light up on every attempt though. If I leave it a while it seems to light again.

Still sound like a blocked jet? If so, how many jets are there and how to get to them and how to unblock them?

Thanks.
Terry

There is only one jet. If it is lighting then that is most likely not your problem. If it is not staying lit, it might be the thermomcoupling. These are not expensive and fairly universal. But it may also be the gas control valve, which are expensive I think.

If changing any item it should be done by a gas safe engineer. But be aware, that you can often get spares online for a fraction of the price caravan dealers charge. Look on the components for identification.

John

 

[JTQ]

First I don't know your particular fridge but I know of generic problems many have.
One thing worth a try first, with a minimum of pulling it apart .

There might be an accumulation of flakes of rust over the burner, flakes that have tumbled down the tube directly over the burner. As these fridges age those that have a history of use on gas "suffer" this problem.

In most cases the burner shield is secured by a single screw that only needs slackening not removing to enable the shield to be removed.
Then with a length of plastic tube you can use this in your mouth as a blow pipe to give the burner a good puff of air to blow the rust dust flakes out of the way. Its on the burner they can be critical to a clean flame

The burner is a little tube the jet fires gas into, it has on top a row of slits, the gas air mix coming out of these slits feeds a flame. With the rust flakes the flame is distributed and so does not always properly heat up the gas failure device, so the gas gets switched off even though it initially lit.
Don't jump in and play with the jet too readily, based on what you have said.
It also could be in a really tiny disc and overly easy to get lost, plus to get there you are getting into gas engineering territory and really need to know a bit about what you are doing, here with regulatory implications.

 

[toad a caravan]

Tel7 have you a manual for the fridge,

 

[JTQ]

From page 32 LINK

This might give you more info LINK

I suspect your burner will be of that type rather than the tube, the rust issue is just the same and very evident in the clip. Try blowing either by mouth tube or better still a compressor fed gun, long before going into it as deeply as the presenter did.

 

[IanB1485]

The selector switch is faulty - had this on several fridges of similar models . A set of contacts on the selector switch , when set on gas carry the small electrical current (20mA) generated by the thermocouple , to the gas valve's internal solenoid keeping it open when the thermocouple is hot. The selector switch contacts are coated with a thin layer of dirt /oil increasing the resistance of the contacts preventing enough current from the thermocouple reaching the gas valves' internal solenoid. the switch can be cleaned , by carefully opening up the two halves of it. and physically cleaning the contacts with isopropyl alcohol( Or use switch cleaner spray , you may be able to inject it without opening up the switch) . Make sure the mains is disconnected from the van as the supply to mains heater on the fridge also passes through this switch. If you are not confident in taking the switch apart ( there are fiddly bits inside) then a new switch is available off the web priced between £44 to £75 dependant on supplier .

 

[ProfJohnL]

Tel7 was kind enough to indicate in his last line that he is in New Zealand. I do not know what the NZ regulations are regarding DIY repairs to gas appliances, You will have to check your local regulations to see what you are allowed to do in respect of gas work.

 

[Tel7]

Tel7 have you a manual for the fridge,

Yes, I have a link to some manuals online, thanks.

 

[toad a caravan]

Usually manuals have a trouble shooting section

 

[Tel7]

The selector switch is faulty - had this on several fridges of similar models . A set of contacts on the selector switch , when set on gas carry the small electrical current (20mA) generated by the thermocouple , to the gas valve's internal solenoid keeping it open when the thermocouple is hot. The selector switch contacts are coated with a thin layer of dirt /oil increasing the resistance of the contacts preventing enough current from the thermocouple reaching the gas valves' internal solenoid. the switch can be cleaned , by carefully opening up the two halves of it. and physically cleaning the contacts with isopropyl alcohol( Or use switch cleaner spray , you may be able to inject it without opening up the switch) . Make sure the mains is disconnected from the van as the supply to mains heater on the fridge also passes through this switch. If you are not confident in taking the switch apart ( there are fiddly bits inside) then a new switch is available off the web priced between £44 to £75 dependant on supplier .

Thanks for that, Ian.
I assume you're talking about the energy selector switch (near the left on the photo below).
How do I remove the energy selector switch? It looks as if I may have to take the front white-ish horizontal strip off first, is that right? If so how? I have already removed two small screws from thecwhite-ish strip, but I can't move it.

 

[IanB1485]

The Spindle holds it in, you just should be able to gently lift it up and it will be released.On the switch will be two black wires that go to the gas solenoid. To test the theory of the faulty switch , short these together and light the gas , if the thermocouple indicator starts to rise into the green when the flame is lit then its the switch . Do not be tempted to permentantly bypass the switch as you won't be able to turn the gas valve off once lit and its not allowed to modify a gas appliance by adding a separate switch.
Don't be fooled by testing the switch with a simple multimeter, a resistance of about 0.5 ohms or higher is enough to stop enough current flowing to hold the gas valve open.

 

[toad a caravan]

 

[Tel7]

The Spindle holds it in, you just should be able to gently lift it up and it will be released. .....

Thanks again, Ian, but I'm confused.

Attached is a similar photo to my last one, but this one is zoomed in on the energy selector.

I can't see how to lift that up. I tried gently pushing the spindle up, but it doesn't budge. And if it did budge, I don't see how I could lift it out anyway.
Or am I supposed to somehow remove the whole block which holds all the controls first, because that looks difficult, especially with the fridge being under a caravan bench.

Please explain what you mean.

Thanks.

View attachment 9119View attachment 9120

Thanks toad a caravan.

That's not quite the same fridge model, but close enough for many purposes.

But the 3 possible causes under "THE REFRIGERATOR DOES NOT COOL IN GAS OPERATION MODE" don't seem to apply to my situation, because:
1. The gas cylinder is not empty as I'm using it for other appliances, and I hear it light up for the fridge.
2. The upstream valve is on, and I haven't touched it since last time I visited the caravan, when the fridge worked on gas.
3. I doubt there is a gas pipe because I hear it light up and I've repeated this a lot of times.

Have I missed anything else?

 

[IanB1485]

Its held down by the shelf above it . To lift it you will have to pull the fridge forward about a 100mm , it is held by four screws located on the inner side walls covered with white plastic caps. At the rear of the fridge the gas pipe may not allow any forward movement ( some have a long piece of 'free copper pipe which will allow the fridge to move forward enough to lift the switch ( about 100mm) .if the pipe is short then it will need to be disconnected and this is were you really need a registered gas engineer as required under NZ regulations as disturbing the gas pipes requires you to ensure once re assembled the gas system is leak free and safe to run, Also you may disturb the sealing around the front face of the fridge and the heat deflector at the back of the fridge .When refitting the fridge you must ensure the fridge is 'room sealed' so that combustion gases can't enter the habitation area.

 

[Mr Grumpy]

After all this good advice if you're still struggling I would strongly urge you to get a mobile engineer round to sort it out for you.

 

[IanB1485]

Not many mobile caravan engineers in new zealand

 

[Mr Grumpy]

Looking like I missed something 🤔

 

[JTQ]

Did you check if the burner was burning clean enough for the thermocouple to work in the first place, as suggested in #5?

As said my experience, as a user who almost exclusively runs on gas has been that rust dust falling from the tube onto the burner can create poor burning, leading to the burner lighting but then go out by failing to set the flame failure device.

A very simple and basic initial check to make. If the flame poorly heats the thermocouple, its has little chance of powering the flame failure device.

 

[Dustydog]

In addition to Ian’s #16 I found it necessary to remove the exterior flue vent and then the flue pipe elbow before moving the fridge forward.

 

[Tel7]

Hi again all,

We're visiting the caravan again for a few days and did some more testing.
I took both Dometic fridge vent covers off the outside of the caraven and took some photos and video (links below).

Through the lower vent hole I see the relection of a small blue flame (maybe just a pilot light) that stays on only until the thermostat dial is released. No change in flame size regarless of what level the thermostat is turned to. If feel some warmth on the metal in front of the flame. Even if we hold the thermostat dial in for a few mins, the flame still goes off when released, except in one of our tests when it continued until we turned it off by turning the fuel selector away from gas mode. None of these tests resulted in any movement of the fridge temperature guage.

Do you have any more specific suggestions of the likely cause and what I may be able to do myself about it, based on this new info?

This photo shows where I saw the flame reflection, a little to the right of the white label. (Flame not visible in photo due to lighting.)

This video shows what I can see through both vent holes.

Thanks again.

 

[IanB1485]

Definitely the selector switch as if the flame lights and the needle does not move it shows the thermocouple circuit is open circuit. There is no such thing as a pilot light, the small flame is the main flame and this produces enough heat to boil the ammonia/water mixture . As I have said in previous posts , the test is to short out the selector switch thermocouple contacts - see first attached picture, the red circle shows the two black wires which are the thermocouple circuit wires. You will need to pull the fridge forward to access these wires and use a short piece of copper wire ( insulated) to short out the connections and then start the fridge normally. This was a faulty fridge I did in the last week or two with the same fault. If it is the selector switch, to remove it it needs to be popped out the white front panel using a screwdriver underneath it. See second attached photo , you can see the red handled screwdriver on the left which was used to lift the switch out of the font panel and the red circle shows the recess in the white panel which holds the selector switch in place. On the switch body there are four clips holding the two halves together, gently prise them off to open the two halves. Once apart you will see the contacts and the switch 'levers'.Its pretty fiddly to clean them and put back together or if unsure to to do this , just buy a new switch assembly . The issue IMO as I have done quite a few of these , is that the manufacturers put too much grease around the contacts and this migrates onto the contacts over time and as the voltage is only about 17 -25mV a thin layer of grease is enough to stop the current from flowing , I found even inserting my DMM in mA current mode into the circuit had enough resistance to prevent the gas valve locking on. The Dial on the gas valve allows different amount of gas to flow but it is very difficult to see the change in the flame height. I know you you New Zealanders are a hardy bunch and very independent so I'm sure you will sort it.

 

[ProfJohnL]

Based on what you have now added to the symptoms, the fact you can see a reflection of a blue flame suggests the flame is burning correctly, it would be more yellow or orange if it was being obstructed, or had a problem with the aeration.

So the problem is the flame is intermittently turned off when you release the gas valve after lighting the gas. This points to a problem with the flame failure thermocouple circuit the purpose of which is to turn the gas off if it looses the flame detection current from the thermocouple. Anything that brakes or impedes the thermocouple's current flow will have the same effect. and Ian's energy selector switch could well do that.

...I found even inserting my DMM in mA current mode into the circuit had enough resistance to prevent the gas valve locking on. The Dial on the gas valve allows different amount of gas to flow but it is very difficult to see the change in the flame height. ...

You are correct , the shunt resistance in most DMM's is enough to limit the thermocouples current such there is not enough current to hold the solenoid valve open.