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-   -   Dometic fridge not working on gas (https://forums.motorhomefacts.com/30-parts-accessories/237171-dometic-fridge-not-working-gas.html)

sheds 16-09-2019 10:25

Dometic fridge not working on gas
 
Hi, we just got back from a three month trip and managed to keep food fresh by hooking up to campsite electricity because our dometic RM7655 fridge won't work on gas. I followed the basic steps of diagnosis by googling and I found that the gas jet is clean, the igniter clicks away happily without igniting any gas, and that if I apply a flame to the burner while the igniter is clicking, not gas flame appears. So I assume no gas is getting to the burner. I checked the 3 electrical connections to the gas valve/solenoid unit and replaced any which looked corroded, but still no gas is flowing. Of course I could test that the control unit is applying a current to the gas valve (if I knew how to do this with my basic gunson electro tester). A replacement gas valve unit is pricey at £155 so I was wondering if anyone can help me with the last step of diagnosis (is current flowing when unit is switched to Gas?) and whether the gas valve is a part I can change given that it involves gas and hence safety.

If not next step is to find a local firm who do dometic fridge maintenance in the Reading area if anyone can advise?

Can anyone give me the basic steps to test the current flow to this device?

thanks

Ian

raynipper 16-09-2019 10:32

Temperamental aren't they. If you can easily access the gas valve try giving it a right whack. You have nothing to lose as all these valves can stick.

Ray.

Webby1 16-09-2019 10:39

Quote:

Originally Posted by raynipper (Post 3050813)
Temperamental aren't they. If you can easily access the gas valve try giving it a right whack. You have nothing to lose as all these valves can stick.

Ray.

After doing all the cleaning it would spark but still not light.

The whack on the gas valve/solenoid freed up something and all is now working well.

sheds 16-09-2019 10:39

As you say, nothing to lose! I did think of this yesterday as it has a solenoid mechanism inside but I was too hot in the sun so will give that a try today as it is cooler here now. I shall also read the Gunson manual to figure out how to test a current flow. Trouble is it needs my partner to be in the van switching the unit on and off gas, and she gets bored doing that! I'm still hoping that we will be allowed to repeat our summer long Greek visit after Oct 31st 2019 as this has been part of our life since retirement in 2007

Drew 16-09-2019 13:01

2 Attachment(s)
This was posted in answer to a similar question by jhelm a few months ago.

Before attempting this isolate both 12 & 240v electric supplies and turn gas off.

Might I suggest that you completely dismantle the gas burner assembly and clear out the debris (Rust) from the burner itself. I will guarantee that you will remove about a tea spoonful of rust. If as you say that you had difficulty in removing the retaining nut, pre soak it with a good squirt of WD40 and leave it for a while. The little jet shown will need a good clean but no attempt should be made to enlarge the hole although it can be cleaned with a Primus Pricker or an extremely fine sewing needle. If you attempt this take care not to lose or damage the jet. Before assembling clean out the flu, most of the debris comes from this.

I believe on an absorption fridge it is impossible to top up the refrigerant.

I used to do this twice a year on my 1993 Hymer that I had for nearly twenty years and never once did it let me down. If you have any questions please ask.

Posted by Eurojohn.

Firstly with the outer vent cover off and the burner shield removed have a helper turn the control from off to gas operation, if the igniter sparks but no flame is produced you can safely assume no gas is being delivered to the burner, the most common reason is dirt, dust, rust covering the top of burner, it is very very unlikely to be a blocked jet as there is an efficient filter / strainer upstream of jet. It is also possible that there is a fault / failure of the gas control device, however that is quite rare, so won't go into detail here.
If you consider yourself proficient enough to carry out DIY repairs you will need a pozi drive No.2 screwdriver, an 11mm open end spanner and a 13mm open end spanner.
Before you start work turn fridge control to off and isolate the gas supply to fridge.
If fitted remove the push on earth connector on burner head (later models don't have separate earth lead) then unplug the igniter and flame failure leads from the control module (they simply push in and pull out) make a note of which one goes where.
Support the square aluminium jet / burner housing with the 13mm spanner and undo the 11mm nut that retains the gas feed pipe into the burner, undo the single No.2 pozi screw that holds the burner assembly to the exhaust tube, allow the burner housing to drop away from exhaust tube and carefully remove the burner assembly, be aware that the jet is simply dropped into the housing and held in place with the feed tube, so is free to fall out and get lost on floor, it is a small pressed dished washer like device that has a tiny hole in the centre. When you have the assembly safely on a clean work surface ensure that the ring of holes at the top of the burner are clear of obstruction and clean if available blow out with compressed air, ensure the jet is actually clear but under no circumstance poke anything in it, the size of the hole is critical to the correct operation of the fridge, so long as the hole is clear and there is no damage to it you will not need a new jet they do not wear. It is possible the flue exhaust will also need cleaning, it's not unknown for them to become blocked by spiders etc. a long bottle type brush is best here , don't try to pull rag through it will get jammed, also if cleaning the flue you will need to access the top of pipe and remove the spiral baffle within the flue before you attempt to clean it, it is simply dropped back in place after cleaning.
Re-assembly is a reversal of dismantling, ensure the jet is correctly placed within the burner (dished end towards burner), at this stage do not replace the burner shield, turn on the gas supply and get your helper to turn control to gas operation, you may need to do this a few times to bleed air out of supply pipe, the burner should now light and stay alight, using a leak detector fluid ensure any joint you disturbed is sound and not leaking. Turn off fridge control and the taking care as the area will now be hot replace the shield and outer covers.


If the burner fires up but fails to stay alight the flame failure device is faulty and you will need to purchase a new burner assembly as they do not supply the flame failure probe separately.


As I mentioned earlier only attempt this if you feel confident to do so otherwise get a qualified and certified person to carry out the repairs for you.

eurajohn 16-09-2019 14:05

Are you sure it's nothing silly like the isolation tap for the fridge gas supply turned off, unusual for no gas to be present at the ignition phase.

If you contemplate the next suggestion you do it at your own peril and you will need to take all necessary precautions.
Firstly switch off the gas supply at your bottle or tank, find the union for the fridge supply and undo nut and release pipe, ensure no external ignition source in the vicinity and then get an assistant to open the supply from your bottle or tank, this should result in gas coming out of the pipe, if not you'll need to find out why.

.

Webby1 16-09-2019 14:27

Quote:

Originally Posted by Drew (Post 3050829)
This was posted in answer to a similar question by jhelm a few months ago.

Before attempting this isolate both 12 & 240v electric supplies and turn gas off.

Might I suggest that you completely dismantle the gas burner assembly and clear out the debris (Rust) from the burner itself. I will guarantee that you will remove about a tea spoonful of rust. If as you say that you had difficulty in removing the retaining nut, pre soak it with a good squirt of WD40 and leave it for a while. The little jet shown will need a good clean but no attempt should be made to enlarge the hole although it can be cleaned with a Primus Pricker or an extremely fine sewing needle. If you attempt this take care not to lose or damage the jet. Before assembling clean out the flu, most of the debris comes from this.

I believe on an absorption fridge it is impossible to top up the refrigerant.

I used to do this twice a year on my 1993 Hymer that I had for nearly twenty years and never once did it let me down. If you have any questions please ask.

Posted by Eurojohn.

Firstly with the outer vent cover off and the burner shield removed have a helper turn the control from off to gas operation, if the igniter sparks but no flame is produced you can safely assume no gas is being delivered to the burner, the most common reason is dirt, dust, rust covering the top of burner, it is very very unlikely to be a blocked jet as there is an efficient filter / strainer upstream of jet. It is also possible that there is a fault / failure of the gas control device, however that is quite rare, so won't go into detail here.
If you consider yourself proficient enough to carry out DIY repairs you will need a pozi drive No.2 screwdriver, an 11mm open end spanner and a 13mm open end spanner.
Before you start work turn fridge control to off and isolate the gas supply to fridge.
If fitted remove the push on earth connector on burner head (later models don't have separate earth lead) then unplug the igniter and flame failure leads from the control module (they simply push in and pull out) make a note of which one goes where.
Support the square aluminium jet / burner housing with the 13mm spanner and undo the 11mm nut that retains the gas feed pipe into the burner, undo the single No.2 pozi screw that holds the burner assembly to the exhaust tube, allow the burner housing to drop away from exhaust tube and carefully remove the burner assembly, be aware that the jet is simply dropped into the housing and held in place with the feed tube, so is free to fall out and get lost on floor, it is a small pressed dished washer like device that has a tiny hole in the centre. When you have the assembly safely on a clean work surface ensure that the ring of holes at the top of the burner are clear of obstruction and clean if available blow out with compressed air, ensure the jet is actually clear but under no circumstance poke anything in it, the size of the hole is critical to the correct operation of the fridge, so long as the hole is clear and there is no damage to it you will not need a new jet they do not wear. It is possible the flue exhaust will also need cleaning, it's not unknown for them to become blocked by spiders etc. a long bottle type brush is best here , don't try to pull rag through it will get jammed, also if cleaning the flue you will need to access the top of pipe and remove the spiral baffle within the flue before you attempt to clean it, it is simply dropped back in place after cleaning.
Re-assembly is a reversal of dismantling, ensure the jet is correctly placed within the burner (dished end towards burner), at this stage do not replace the burner shield, turn on the gas supply and get your helper to turn control to gas operation, you may need to do this a few times to bleed air out of supply pipe, the burner should now light and stay alight, using a leak detector fluid ensure any joint you disturbed is sound and not leaking. Turn off fridge control and the taking care as the area will now be hot replace the shield and outer covers.


If the burner fires up but fails to stay alight the flame failure device is faulty and you will need to purchase a new burner assembly as they do not supply the flame failure probe separately.

.

And THEN give it a good smack :wink2::wink2:

Drew 16-09-2019 14:32

Hi it with a hammer, with a hammer said the fitter,
Very fine men are we,
There's non so fair as can compare,
With the boys of ****.

Your as bad as Ray.

raynipper 16-09-2019 15:38

I used to work on the VC10 aircraft at Weybridge Surrey and often had a snag list to sort out while on nights.
On tropical trials the odd fuel transfer valve would get stuck and they would fly the aircraft back to Weybridge where a fuel fitter climbed into the 'torque' box between the wings and take out the offending valve to change for a new one.
We soon twigged that using a long lump of wood we could just open the hatch and give the 'stuck' valve a whack with the timber and voila working again.

Never heard of any further stuck valves while in service.
In fact that lump of timber was kept in the stores labeled "Fuel Valve Actuator".

Ray.

sheds 16-09-2019 19:45

I have checked the jet and cleaned the burner. The problem is that no gas is arriving down the pipe to the burner. I have made sure the isolator tap for the fridge is open i guess the last thing would be to check that gas is arriving at the solenoid valve, thereafter its off to drain the bank account for a new one.......


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