Troubleshooting Dometic RMS 8501 Fridge Issues (1 Viewer)

[RustyRuss]

Hi guys. VERY frustrated! I want to enjoy our Moho. The Dometic fridge is a complete and utter piece of JUNK! It’s an RMS8501 and guess what, it doesn’t work on gas! The pipe work is getting hot at the back of it, I’ve vacuumed it and cleaned the igniters and the chimney gets too hot to touch, I’ve checked the thermistor with my multimeter and it’s dropping in resistance as the temperature rises, but the useless piece of sh1t isn’t cooling even slightly! I put a new front control panel on it 2 years ago (£245!!! Dometic ROBBING BARSTEWARDS!!) that’s probably the worst fit for an original equipment piece of kit I’ve EVER come across! What do I have to do to get the f****er to work? Get on my knees and beg? Some of you guys must have come up with a solution. Please Help!

I’ve been trying to get it to work all day and now I want to drag it out of the Moho and beat it to death with a sledgehammer!

Think I’m a little tired and emotional…….

Sorry to loose my cool, can any of you guys suggest what’s wrong with the heap of junk?

Or can you suggest a compressor alternative to replace it please?


Yours weeping in rage and frustration,
Russ

 

[DJT]

The fridge isn’t working and now you’ve lost your cool!!
A double whammy!!
Sorry Russ couldn’t resist.
Someone will be along with an answer before long

 

[Figaro]

Is it the same on 12v 230v and gas ?
Have you tried replacing the thermal transfer paste ?

 

[Abacist]

Mine only works on gas and 12 volts. I got mains elements replaced then intermittent fault on mains and now nothing on EHU.

I did fit CBE cooling fans behind the top vent to improve air flow and can’t fault it on gas or 12 volts.

 

[RustyRuss]

Is it the same on 12v 230v and gas ?
Have you tried replacing the thermal transfer paste ?

Thermal transfer paste? Where is that likely to be lurking and how and where will I apply and get it from? Thanks for the reply!

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[RustyRuss]

Mine only works on gas and 12 volts. I got mains elements replaced then intermittent fault on mains and now nothing on EHU.

I did fit CBE cooling fans behind the top vent to improve air flow and can’t fault it on gas or 12 volts.

Where are the mains elements?

 

[Figaro]

There should be an aluminium plate with fins in the fridge
The cold gases pass behind this plate and there is transfer paste that transfers the cold to the fins and they cool the fridge
It's the stuff computer builder set the chips in the heat sink to disipate the heat, just working in reverse in the case of a fridge.
I replaced mine on a different model Dometic fridge and it made a big difference to performance
Lots of info on here if you do a search

 

[DavidG58]

Ours lost its refrigerant some years ago , we knew due the ammonia like smell, not sure if that stops it cooling on only gas or gas and electric , terminal in our case

Only slight benefit you have yours probably isn’t attached to the oven bit

 

[ManTheVan]

For thermal paste, go to Amazon or EBay and search for it. You’ll find it in the computer sections, as it’s commonly used to join a computer’s CPU to the motherboard. It should cost you about £5-6. You’ll need a marmite tub’s worth of it, approximately.
Open the fridge and remove the shelves, then unscrew the aluminium fins at the rear of the fridge. Clean off the old gunk (expired thermal paste) and butter on the new paste to the back of the fins, then screw back on. Do the same in the freezer compartment. Make it a decent, thickly buttered job.

If that is the issue, this will solve the problem. If the issue is that you’ve had a refrigerant leak, then no amount of paste will resolve it. You’ll need to get a refrigerant refill in that case.

Good luck.. it’s an easy job that will take you no more than 20 mins.

 

[RustyRuss]

To show commitment, and dedication to the cause I’ve just been outside in my negligee to check that it’s cooling on the EHU, which I plugged in at 7.30pm. For those that come to this thread in the am, it’s now 23.48 hours. The blighter is working! I don’t know whether to laugh or cry! I still want the swine to work on gas though, just in case we go of grid in the near future. I also want to be sure that it’s going to work properly when we go to Il de Rey in June. Just want to swear a lot at the contemptible piece of junk! What’s the matter with making things work properly and not be prone to being unreliable?! GRRR!!! My experiences with anything made by Dometic is their build quality, materials and reliability are all rubbish, very expensive, impossible to get spares for, but still rubbish.

Obviously still tired and emotional……..

Off to my pit now, catch you all in the morning when hopefully I’ll have had suggestions for a solution, OR a replacement with a compressor!

Thanks for listening!

Russ

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[RustyRuss]

For thermal paste, go to Amazon or EBay and search for it. You’ll find it in the computer sections, as it’s commonly used to join a computer’s CPU to the motherboard. It should cost you about £5-6. You’ll need a marmite tub’s worth of it, approximately.
Open the fridge and remove the shelves, then unscrew the aluminium fins at the rear of the fridge. Clean off the old gunk (expired thermal paste) and butter on the new paste to the back of the fins, then screw back on. Do the same in the freezer compartment. Make it a decent, thickly buttered job.

If that is the issue, this will solve the problem. If the issue is that you’ve had a refrigerant leak, then no amount of paste will resolve it. You’ll need to get a refrigerant refill in that case.

Good luck.. it’s an easy job that will take you no more than 20 mins.

Thanks for that! I’ll give it a go when I’ve exhausted electrical twiddling, will the paste affect how it works on 230v as it seems to be working on EHU?

Thanks!

Russ

 

[RustyRuss]

The fridge isn’t working and now you’ve lost your cool!!
A double whammy!!
Sorry Russ couldn’t resist.
Someone will be along with an answer before long

A glimmer of a smile has passed my lips for the first time today…..

 

[ManTheVan]

Thanks for that! I’ll give it a go when I’ve exhausted electrical twiddling, will the paste affect how it works on 230v as it seems to be working on EHU?

Thanks!

Russ

No, the paste will just make sure that the heat is conducted out of the fridge. If it’s working on EHU that IS 230V! Should also work on gas and 12V in that case.

 

[TinaLes]

I took our new at the time Carthago van back to the dealership when it was a month old as the Dometic FF didnt get cool on gas or electric, and we had to dump all our food whilst away on a 4 day rally event.
The dealership asked me to call Dometic and see if they could get a mobile engineer to come to our house and fix it under warranty. I tried every listed Dometic engineer in Surrey, Sussex & Berkshire, and they were all booked up for months!
In sheer frustration, I drove the van 120 miles back to the dealership, and told them it might as well sit on their forecourt as apposed to my drive as it cannot be used without a fridge.
It was only then that I discovered they did not have an in house Dometic Service engineer, they used a mobile chap.
He came along to the dealership, checked the FF over and diagnosed after a couple of hours that the cooler unit probably had a leak, therefore was not cooling.
He returned a week later, with the new cooling unit, ready to take the whole fridge, freezer out, split in half (back & front) and replace the rear cooling unit, which would have been a very tight job to do inside the MH.
He then discovered much to his surprise, that the existing FF was very cold and the freezer was working even better than average! He had left the van on EHU hook up for a week before returning with the new parts, only to find it was working perfectly, and I got the good news to come and collect the van, all was working.
I went down stayed overnight at the dealership and sure enough all was well.
I then realised that the van parked at home for a month on our sloping drive was the problem.
The coolant was not level at the bottom of the heat exchanger, and would not circulate when heated. It needed a few days on a level ground for the coolant to find its level in the pipes at the rear.
I got over this by building permanent ramps to level the van front to rear, all has been well ever since...touch wood.
So the question is....is your van parked on the level?
Good Luck.
LES

 

[Tricky One]

Hi guys. VERY frustrated! I want to enjoy our Moho. The Dometic fridge is a complete and utter piece of JUNK! It’s an RMS8501 and guess what, it doesn’t work on gas! The pipe work is getting hot at the back of it, I’ve vacuumed it and cleaned the igniters and the chimney gets too hot to touch, I’ve checked the thermistor with my multimeter and it’s dropping in resistance as the temperature rises, but the useless piece of sh1t isn’t cooling even slightly! I put a new front control panel on it 2 years ago (£245!!! Dometic ROBBING BARSTEWARDS!!) that’s probably the worst fit for an original equipment piece of kit I’ve EVER come across! What do I have to do to get the f****er to work? Get on my knees and beg? Some of you guys must have come up with a solution. Please Help!

I’ve been trying to get it to work all day and now I want to drag it out of the Moho and beat it to death with a sledgehammer!

Think I’m a little tired and emotional…….

Sorry to loose my cool, can any of you guys suggest what’s wrong with the heap of junk?

Or can you suggest a compressor alternative to replace it please?


Yours weeping in rage and frustration,
Russ

Have similar problem with my Dometic 8555. Now listed as obsolete and few if any parts available. Going to junk it in favour of a Thetford T2160 Compressor FF. Leisure Direct and Jacksons have them on around £1390 pp £39.

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[RustyRuss]

I took our new at the time Carthago van back to the dealership when it was a month old as the Dometic FF didnt get cool on gas or electric, and we had to dump all our food whilst away on a 4 day rally event.
The dealership asked me to call Dometic and see if they could get a mobile engineer to come to our house and fix it under warranty. I tried every listed Dometic engineer in Surrey, Sussex & Berkshire, and they were all booked up for months!
In sheer frustration, I drove the van 120 miles back to the dealership, and told them it might as well sit on their forecourt as apposed to my drive as it cannot be used without a fridge.
It was only then that I discovered they did not have an in house Dometic Service engineer, they used a mobile chap.
He came along to the dealership, checked the FF over and diagnosed after a couple of hours that the cooler unit probably had a leak, therefore was not cooling.
He returned a week later, with the new cooling unit, ready to take the whole fridge, freezer out, split in half (back & front) and replace the rear cooling unit, which would have been a very tight job to do inside the MH.
He then discovered much to his surprise, that the existing FF was very cold and the freezer was working even better than average! He had left the van on EHU hook up for a week before returning with the new parts, only to find it was working perfectly, and I got the good news to come and collect the van, all was working.
I went down stayed overnight at the dealership and sure enough all was well.
I then realised that the van parked at home for a month on our sloping drive was the problem.
The coolant was not level at the bottom of the heat exchanger, and would not circulate when heated. It needed a few days on a level ground for the coolant to find its level in the pipes at the rear.
I got over this by building permanent ramps to level the van front to rear, all has been well ever since...touch wood.
So the question is....is your van parked on the level?
Good Luck.
LES

How interesting! The Moho is on a slight slope. I don’t normally worry about getting it absolutely plumb when it’s on the driveway, which it has been for over a month bar being in Sheffield last weekend. It’s back in the same spot as before on the drive now, tail down, fridge on drivers side. It was working on mains/EHU at midnight last night. I’ll get it absolutely plumb this morning and see how that works. Thanks for that Les! IF this is the solution does it imply that some of the refrigerant has leaked out? Can the unit be re-gassed by an Aircon specialist at my local, tame, garage?

Russ

 

[RustyRuss]

No, the paste will just make sure that the heat is conducted out of the fridge. If it’s working on EHU that IS 230V! Should also work on gas and 12V in that case.

I’m an electrician, I had a reasonably good idea that the EHU plugged into a waterproof socket n the wall of the house would give me 230ish volts, but thanks anyway. Others reading this may not be quite so savvy, so thanks, a good point, well made!

Russ

 

[Hettie's Crew]

Thermal transfer paste? Where is that likely to be lurking and how and where will I apply and get it from? Thanks for the reply!

3way fridge thermal gel replacement ?

As previously discussed have received the tube of thermal gel and dismantled the fridge cooling fins which shows no sign of the old gel.Where does the gel (copper paste ) go.. between the screws or where it goes around the black tubes? Also does it go on tubes before the freezer plate slides...

www.motorhomefun.co.uk

Baffle

Anyone know where the fridge baffle hangs from?

www.motorhomefun.co.uk

I replaced the paste on mine and fitted a baffle into the chimney, after cleaning it and it works great. No3 on gas, No4 on EHU.

 

[Abacist]

Where are the mains elements?

About half way up the back between the 2 external vents. I watched a German Dometic Mobile engineer do it completely by feel as there is no way you can see them. If it works on electric they are fine and don’t need changing.

 

[RustyRuss]

About half way up the back between the 2 external vents. I watched a German Dometic Mobile engineer do it completely by feel as there is no way you can see them. If it works on electric they are fine and don’t need changing.

So logic implies that the electric elements heat the same refrigerant in the same tubing as the gas burner, just in different places. TinaLes established that having the van level made the refrigerant circulate properly, does it then follow that once you’ve got the useless bar steward working on EHU just swap it to gas and it should run?

What thoughts people?

Russ

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[Hettie's Crew]

So logic implies that the electric elements heat the same refrigerant in the same tubing as the gas burner, just in different places. TinaLes established that having the van level made the refrigerant circulate properly, does it then follow that once you’ve got the useless bar steward working on EHU just swap it to gas and it should run?

What thoughts people?

Russ

Yes, basically but the right amount of heat has to be produced in order for it to work. 12v can’t produce enough heat and is just there to maintain whilst driving. The two main sources of heat are the 240v and gas. The electric elements are in contact with the lower tubes and apply heat to the Water, Ammonia, Chromate and Hydrogen mix to make the refrigerant process work.
The gas flame has a chimney and has to be restricted or baffled to prevent most of the heat just going straight up the chimney and out the top, so it gets concentrated around the lower tubes.
It should burn blue with no white flame.
These fridges don’t produce cold in the compartment they absorb heat from it, which is why it’s important to have the best thermal bridge from the aluminium finned plate to the rear pipe work, hence replacing/renewing the paste.
Some fridges were fitted, by the converter without the baffle in the chimney resulting in poor performance on gas. Though, some fridges aren’t specified to have a baffle.
Being level will result in best performance because of the way the refrigerant mix flows back down.

 

[Figaro]

If it's cools properly on any energy sources it won't be the thermal paste that's the problem, although as it's such a simple job it might be worth doing anyway as it definitely gives a worthwhile benefit.
Get the van level and then test on each energy source

 

[Fdhadi]

We are also having problems with our Dometic RML9335 but on 12v only.
It buzzes away when the engine is started.
I believe it has 2 x fuses so will try to find those and check these first.

If the fuses aren’t the problem, where should I start looking next?

 

[jockaneezer]

Fdhadi, if it's making a buzzing sound, that generally means a relay isn't working/latching properly and will need replacing. See if you can follow the sound to find the offending item.

 

[tonyidle]

Yes, basically but the right amount of heat has to be produced in order for it to work. 12v can’t produce enough heat and is just there to maintain whilst driving. The two main sources of heat are the 240v and gas. The electric elements are in contact with the lower tubes and apply heat to the Water, Ammonia, Chromate and Hydrogen mix to make the refrigerant process work.
The gas flame has a chimney and has to be restricted or baffled to prevent most of the heat just going straight up the chimney and out the top, so it gets concentrated around the lower tubes.
It should burn blue with no white flame.
These fridges don’t produce cold in the compartment they absorb heat from it, which is why it’s important to have the best thermal bridge from the aluminium finned plate to the rear pipe work, hence replacing/renewing the paste.
Some fridges were fitted, by the converter without the baffle in the chimney resulting in poor performance on gas. Though, some fridges aren’t specified to have a baffle.
Being level will result in best performance because of the way the refrigerant mix flows back down.

The 12V element is little different to the 230V element in terms of heat output and correctly connected with appropriately sized wiring will perform as well as any other heat source. 12V running gained a poor reputation because of the lengthy and inadequate wiring run used in caravans. Some MH converters try to replicate this inadequacy by using thin wiring. A check is to measure the voltage at the fridge itself when running on 12V - you might be surprised.

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[TinaLes]

How interesting! The Moho is on a slight slope. I don’t normally worry about getting it absolutely plumb when it’s on the driveway, which it has been for over a month bar being in Sheffield last weekend. It’s back in the same spot as before on the drive now, tail down, fridge on drivers side. It was working on mains/EHU at midnight last night. I’ll get it absolutely plumb this morning and see how that works. Thanks for that Les! IF this is the solution does it imply that some of the refrigerant has leaked out? Can the unit be re-gassed by an Aircon specialist at my local, tame, garage?

Russ

The quoted allowance from Dometic I think was that the van should be level +or- 5% for the FF to perform at its best.
In my case the van was parked up for a month at much more than that, but as it was parked up not being used I thought no more of it.
What I didnt realise was how long it would take for the gas fluid stuff to find its level again. As mentioned mine took a few days on level ground to find its own level, but as its a sealed unit no gas had escaped. I have no idea of the viscosity of the cooling fluid, maybe others will know, but it still took a while, with I presume with FF set to max cold for the cooling fluid to start to circulate and the FF to start cooling.
Good luck, I hope it works for you when you get the van leveled, let us all know the outcome.
LES

 

[Just smiffy]

Baffle… check that it has a baffle in the chimney, I had this problem and it solved it completely….

It’s the curly thing that hangs down the chimney…

 

[RustyRuss]

Baffle… check that it has a baffle in the chimney, I had this problem and it solved it completely….

It’s the curly thing that hangs down the chimney…

View attachment 892505

Smiffy I’m definitely baffled! I had the baffle out and the flue vacuumed and I reinserted it correctly. Thanks for your suggestion though.

Russ

 

[TinaLes]

RustyRuss I should have mentioned that when I had the problem with the van not being level, therefore not cooling, if I ran it on gas it would spark up ignite & run only for a short while, as the burner reached its temp the thermostat kicked in and turned the gas off until the heating element cooled back down, then it would repeat, fire up for a short while then turn off again.
This should have been an indication that the coolant was not circulating, if it was circulating as it should then the burners would run longer and the fridge start to cool inside. I had exactly the same problem with the 240V mains elements as they would cut out also.
I am not aware of any method of getting the coolant to settle where it should at the bottom, other than leveling the van for a few days, then re-trying the warming process via electric or gas. A fridge/air con engineer would probably use a pressure gauge to check coolant pressure, but I have no idea how they get it to circulate.
Any luck yet leveling the van?
LES

 

[RustyRuss]

I had to take the van back to storage yesterday as I needed the MX5 I’d used to go and get it in the first place, I’m bringing it back next weekend for another play, will definitely let you know how I get on. I got it to work really well on the EHU, do you think that will have got the refrigerant circulating properly? I know I can get the gas to light and make the chimney too hot to touch, but not cool the fridge. Thanks for all your suggestions so far.

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