ADVICE NEEDED - Dometic RM7655L Freezer cold fridge warm

[ItaMotorhomer]

Hi

As per above title, I’m struggling to find the cause of why our fridge doesn’t cool as it should OR I’m I asking to much?

the Motorhome was bought 3 months ago (2005 Burstner) and while away in warm (ish) weather (around 25 degrees) we noticed the fridge wasn’t cooling. The temperature inside the fridge was around 17 degrees.

THE FREEZER however was reading -6 degrees

So we took it back to the dealers we bought it from only to be told they had run some tests and didn’t find anything wrong with it.

Their test showed:
-Run the fridge on both, 240 and gas and recorded readings. After 4-6 hours of operation their readings showed fridge temperature was around 5-7 degrees (note this completely empty fridge) on both fuels.

So we went and collected the Motorhome back got back home and started doing some tests - note the weather now is a lot cooler compared to when we found it was reading around 18 degrees back in the warm summer week we had


Anyway plug on 240 first let it run for around 8 hours internal temperature was 9 degree


Switch it off for the night the next day switch it on gas after approx 7 hours it was reading 7 degrees (empty fridge)


NOTE the freezer was reading -19 degrees


I since did a bit of research and came across few posts here about replacing the thermal paste behind the metal fins so… great I thought order some GD900 from Amazon and got on with the job


Taken the fins out and found the old paste (grey colour ) was all very dry scrap it all out and clean the back of the fins, then went to clean the black condenser pipe and applied 2 x30g tubes of the GD900. Fitted everything back and spend the last 2 days restrung it all again only to find - very little to no difference

Could anyone more experienced then me suggest any other possible causes/fixes ??

Is the black condenser pipe that runs behind the fins the same for both fridge & freezer ?

I find very strange that the freezer cools down to -19 and the fridge struggles ?

Is 7/9 degrees normal for this fridge (empty)?

Any suggestions will be greatly appreciated

Thanks

 

[GeoffnDee]

Is it possible that the fridge door needs adjusting (if this can be done) or its seal replacing ?

 

[Just smiffy]

These fridges seem to work best on 2-3 setting, if you turn it up to 4-6 it gets hotter, I know that don’t makes sense but it does seem to work,

What setting are you on….

 

[ItaMotorhomer]

Is it possible that the fridge door needs adjusting (if this can be done) or its seal replacing ?

Seal looks good

 

[ItaMotorhomer]

These fridges seem to work best on 2-3 setting, if you turn it up to 4-6 it gets hotter, I know that don’t makes sense but it does seem to work,

What setting are you on….

I’ve tried on pall 4 levels, none seem to get it any cooler

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[GeoffnDee]

Faulty temp. sensor or its connection to the power module ?

 

[ItaMotorhomer]

Faulty temp. sensor or its connection to the power module ?

No no idea sorry does this helps ?

 

[Vikdikdok]

Are you level as these fridges are notorious for not working properly if van not level

 

[ItaMotorhomer]

Are you level as these fridges are notorious for not working properly if van not level

I’d have to say it’s currently parked on my drive which is slightly slopped so tomorrow I’ll put it on the levelling ramps and repeat the testing

 

[GeoffnDee]

No no idea sorry does this helps ?



View attachment 957439

I think the temp. sensor should be on the cooling fins inside the fridge and is connected to the control module that is behind the control panel
There is a service manual for the Dometic 7 series fridge that may help on page 4 of Manuals for Motorhome stuff section of resources (shown at the bottom of this page)

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[Richard n Ann]

Is the black condenser pipe that runs behind the fins the same for both fridge & freezer ?

Yes.
Next I would take the fins off in the fridge and switch it on. The black pipe should frost up, a hard frost that your finger sticks to

 

[rb62]

Two 30g tubes sounds far to much to have used,it only needs to be put on very thinly.

Tube and half the first time

Half a tube the second time and you’ve seen the results

 

[WESTY66]

Two 30g tubes sounds far to much to have used,it only needs to be put on very thinly.

Yes, second time using less has had better results

 

[Thornebt]

My Thetford fridge struggles to get down to temperature in warm weather. I freeze two 2 litre bottles of water in my home freezer and put those in the fridge before a trip. The fridge is then ok, maybe it struggles a bit to stay cool on 12v when driving.

I've also bought a wireless fridge thermometer. That enables me to know the temperature of the fridge without opening the door and filling it with warm air!

 

[ItaMotorhomer]

Yes.
Next I would take the fins off in the fridge and switch it on. The black pipe should frost up, a hard frost that your finger sticks to

Hi Richard

So if this his the case, if the freezer works (-19 degrees) the fridge should be working to??

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[ItaMotorhomer]

Yes, second time using less has had better results

When you say less how much please ? One tube (30g)?

 

[EuroTrotters]

These fridges seem to work best on 2-3 setting, if you turn it up to 4-6 it gets hotter, I know that don’t makes sense but it does seem to work,

What setting are you on….

It can make perfect sense.

If the setting is too high and the fridge cannot attain the required temperature, the evaporator starts to accumulate hoar frost.

This is because the appliance does not cycle into a static defrost mode (off cycle).

So if the evaporator or cooling fins should be at -5c, as an example, the hoar frost formation becomes an insulant, raising the temperature of the surface.

This means there is less heat transfer. Resulting in reducing cooling efficiency.

The easiest way to understand it, think of it as an Igloo Effect. Frost or ice around the evaporator !

ET

 

[Thornebt]

That is an impressive reply from ET. It's convinced me to set my fridge on setting 2 in future.

 

[Richard n Ann]

Hi Richard

So if this his the case, if the freezer works (-19 degrees) the fridge should be working to??

Yes, if it doesn't there is either a blockage or not enough refrigerant in it

 

[Thornebt]

Yes, if it doesn't there is either a blockage or not enough refrigerant in it

Can you add refrigerant?

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[EuroTrotters]

That is an impressive reply from ET. It's convinced me to set my fridge on setting 2 in future.

Just keep an eye on the frost build up. If it's not changing from frost to condensate (sweating). Simply turn it down or even off for a little while to allow the hoar frost to melt.

You usually only get these issues with leisure fridges when the ambient temperature is high along with high humidity.

That or door not closing or gap in gaskets.

 

[Richard n Ann]

Can you add refrigerant?

No not on these absorption fridges. It would have to go back to the factory, and they wouldn't get involved so it's scrap

 

[Richard n Ann]

Just keep an eye on the frost build up. If it's not changing from frost to condensate (sweating). Simply turn it down or even off for a little while to allow the hoar frost to melt.

You usually only get these issues with leisure fridges when the ambient temperature is high along with high humidity.

That or door not closing or gap in gaskets.

Mine always used to half frost up from the right hand side, I used to defrost it every couple of weeks. Used to have the stat set on about 1/3rd

 

[EuroTrotters]

Can you add refrigerant?

Not on 3-way, its amonia

You can on compressor refrigeration. But they should never need it as they are hermitically sealed for life.

 

[WESTY66]

When you say less how much please ? One tube (30g)?

Prob half of that

As an aside, my fridge works best on 4 it’s minus 19 in the freezer and around 3-4 in the fridge, if I put it on 3 it goes to minus15 in freezer and 7-8 in fridge! I have to say it’s working great since I fettled it properly with the help of Paul Two on Tour

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[ItaMotorhomer]

Prob half of that

As an aside, my fridge works best on 4 it’s minus 19 in the freezer and around 3-4 in the fridge, if I put it on 3 it goes to minus15 in freezer and 7-8 in fridge! I have to say it’s working great since I fettled it properly with the help of Paul Two on Tour

Thanks for all the replies