Any suggestions for fixing Dometic fridge cooling issue?

[Pete and Liz]

Hi All
Early Happy New year and safe travels for 2024 to you all.

As we have the MH on the drive I ,like many of you probably did, wanted to use the fridge as a beer wine overflow chiller for the festive season. Now we haven't used the MH since November ,when all worked ok, but when I turned on the fridge (Dometic RMDT8505 ) to auto with the hook up plugged in I found after 6 hours it was not even vaguely chilled. The MH is about 40 months old and so the fridge is roughly the same age so this was not expected. I have carried out the normal checks:
Q: Is the 230v working Q:Yes
Q: Are there any alarms or symbols on the fridge control panel A: No
Q: Are there any fuses blown A: No
Q: Does it work on Gas A: Yes
Q: Do the 230V heating elements get hot A: Yes (dam hot)

So I am a bit stumped as I was expecting it to be an element failure , although I haven't checked the resistance but the fact they get hand burning hot makes me think that they are ok. I have done the usual searching through the posts and inter web but most examples of failures either have no power to the element or alarms on the panel.

So my question to the collective is what else can I check? Is there some form or reset for the control brick?

TIA

 

[Two on Tour]

Maybe it requires the winter covers on the vents if the outside air temperature is too cold.

 

[Pete and Liz]

Maybe it requires the winter covers on the vents if the outside air temperature is too cold.

Its only been between +4C and +7C now so not that cold but I will give that a try thanks.

 

[Two on Tour]

Its only been between +4C and +7C now so not that cold but I will give that a try thanks.

I seem to remember Dometic saying in their literature to fit them below 10 deg C.

 

[rosalan]

Almost certainly the fridge fins are not in contact with the cold freezer pipe at the back. You could try tightening the screws inside the fins a tiny bit to make better contact. Otherwise remove the 7 screws and gently pull away the fins taking care of the attached sensor. With the fins removed you can better understand the problem. The fin unit has to make contact with the freezer pipe behind via a very thin layer of thermal plastic. The fridge cold comes from the contact with this cold pipe. You may need to buy new thermal paste if yours has broken down. This is not a difficult job if you can avoid bending the fins.

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[Pete and Liz]

Almost certainly the fridge fins are not in contact with the cold freezer pipe at the back. You could try tightening the screws inside the fins a tiny bit to make better contact. Otherwise remove the 7 screws and gently pull away the fins taking care of the attached sensor. With the fins removed you can better understand the problem. The fin unit has to make contact with the freezer pipe behind via a very thin layer of thermal plastic. The fridge cold comes from the contact with this cold pipe. You may need to buy new thermal paste if yours has broken down. This is not a difficult job if you can avoid bending the fins.

I did think of that but foolishly dismissed the idea as the fridge is only 40 months old and works on gas. I will order a tube and give that a go thanks.

 

[namwaldog]

There are very comprehensive Installation and service manuals for your Dometic Fridge Freezer in the Resources Section.

Click the Menu Bars and scroll down to Resources
They were uploaded August 2020 so midway on page 4.

Good Luck

 

[rosalan]

Interesting, mine was almost exactly the same age when I had the problem, just out of warranty. It seems to be a common problem but when I contacted three different Dometic agents, their opinion was to replace the internal unit, then I met another Dometic repair man who explained this simple repair, which worked. Although first time I used too much mastic before learning how thin the layer should be. Basically if the freezer works ok, this must be the answer.

 

[bigtwin]

Almost certainly the fridge fins are not in contact with the cold freezer pipe at the back. You could try tightening the screws inside the fins a tiny bit to make better contact. Otherwise remove the 7 screws and gently pull away the fins taking care of the attached sensor. With the fins removed you can better understand the problem. The fin unit has to make contact with the freezer pipe behind via a very thin layer of thermal plastic. The fridge cold comes from the contact with this cold pipe. You may need to buy new thermal paste if yours has broken down. This is not a difficult job if you can avoid bending the fins.

But it works fine on gas so that rules that failure mode out.

Ian

 

[bigtwin]

Q: Do the 230V heating elements get hot A: Yes (dam hot)

When did you check the temperature?

Both the gas and electric element heat the same area. You didn’t check after you'd run it on gas did you?

Ian

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[Pete and Liz]

Whe

When did you check the temperature?

Both the gas and electric element heat the same area. You didn’t check after you'd run it on gas did you?

Ian

No I checked the heating element before going on to gas.

And just removed the fins and the pipe at the back is not cold on mains but the thermal compound is still very pliable and sticky, but I will change it no I have disturbed it.

I am let the element cool down and check the resistance , does anyone know what it should be or the wattage so I can work it out?

 

[1967bowesj]

Whe

No I checked the heating element before going on to gas.

And just removed the fins and the pipe at the back is not cold on mains but the thermal compound is still very pliable and sticky, but I will change it no I have disturbed it.

I am let the element cool down and check the resistance , does anyone know what it should be or the wattage so I can work it out?

Think the wattage varies but will be somewhere near this one that prima have listed.

Element

 

[Pete and Liz]

Whe

No I checked the heating element before going on to gas.

And just removed the fins and the pipe at the back is not cold on mains but the thermal compound is still very pliable and sticky, but I will change it no I have disturbed it.

I am let the element cool down and check the resistance , does anyone know what it should be or the wattage so I can work it out?

Just found there service manual in the resources section , thanks Namwaldog, and it say the resistance of the element is approx 350 Ohms so P=V2/R or 52900/350 = 151 W element

 

[1967bowesj]

On a side note, are there no fail warning lights?
I ask as that model group havea bit of issues with the rear low circuit board.I would check all connections on that to make sure there’s no easy obvious faults.

 

[Lenny HB]

There is another thread with similar problems I think it was haganap.
Working on gas but not on mains, I believe the conclusion was that it was a partial blockage in the refrigerant. The refrigerant gets hotter on gas which overcomes the problem. The fix is a new cooling unit which I think is around £600.

Edit:
Found the thread.

Dometic RMDT8505 fridge freezer - not cooling on Mains Electric

This works fine on both gas and 12 volts but is not working on 240 mains voltage, or if it is, it is not noticeably performing any cooling or freezing function. The unit does not display any of the handbook error lights or beeps but seems happy to apparently operate on the mains button. The...

www.motorhomefun.co.uk

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[Pete and Liz]

On a side note, are there no fail warning lights?
I ask as that model group havea bit of issues with the rear low circuit board.I would check all connections on that to make sure there’s no easy obvious faults.

No fail light or bleeps of any kind. I can make it bleep by manually setting it to GAS ands turning it off or 12V or 230v so you would think the auto detect part of the electronics is working.

 

[Pete and Liz]

There is another thread with similar problems I think it was haganap.
Working on gas but not on mains, I believe the conclusion was that it was a partial blockage in the refrigerant. The refrigerant gets hotter on gas which overcomes the problem. The fix is a new cooling unit which I think is around £600.

Edit:
Found the thread.

Dometic RMDT8505 fridge freezer - not cooling on Mains Electric

This works fine on both gas and 12 volts but is not working on 240 mains voltage, or if it is, it is not noticeably performing any cooling or freezing function. The unit does not display any of the handbook error lights or beeps but seems happy to apparently operate on the mains button. The...

www.motorhomefun.co.uk

If it's going to be that expensive I will replace it with a compressor fridge as I had them before with no problems.

 

[Lenny HB]

If it's going to be that expensive I will replace it with a compressor fridge as I had them before with no problems.

Probably be a days labour on top of that.

289035240 DOMETIC FRIDGE COOLER UNIT

www.swordcrowncaravans.com

 

[bigtwin]

Just found there service manual in the resources section , thanks Namwaldog, and it say the resistance of the element is approx 350 Ohms so P=V2/R or 52900/350 = 151 W element

Yes, that’s about right. Calculating back from a 185W element gives a resistance of 311 Ohms.

Ian

 

[Fragle]

No fail light or bleeps of any kind. I can make it bleep by manually setting it to GAS ands turning it off or 12V or 230v so you would think the auto detect part of the electronics is working.

In our new to us 3 year old van. First time out all looking great no fault lights etc. But the fridge didn’t cool. So much for the pre handover check. Connection to 240v overnight and no difference. Cancelled the break and van went back. They changed some parts but still no good. In the end they fitted a new one as they could not find the problem.
Looks like 3 years is the dometic problem time. Any problems with this one in the future I will change to compressor fridge

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[haganap]

If it's going to be that expensive I will replace it with a compressor fridge as I had them before with no problems.

Mine is yet to be repaired, being fixed under warranty in a few weeks.

3 possibilities.
1) heating element which you've ruled out.
2) the pcb unit at the back of the fridge, known to be a common fail.
3) in my case cooling unit .. you can look at the pipe work. Turn the fridge on electric for a few hours, feel the pipe work as it travels up ( careful could be hot)
Then feel where it returns., if cooler then a blockage could be identified. Then repeat process on gas and you may note the pipe work is hot all the way round.
This is because gas can produce more power and push through the blockage.

There is a cheaper solution to repairing, which is to remove the fridge and shake and turn upside down.. (check you YouTube). This can resolve but generally always comes back at some point.

Good luck

 

[Pete and Liz]

Mine is yet to be repaired, being fixed under warranty in a few weeks.

3 possibilities.
1) heating element which you've ruled out.
2) the pcb unit at the back of the fridge, known to be a common fail.
3) in my case cooling unit .. you can look at the pipe work. Turn the fridge on electric for a few hours, feel the pipe work as it travels up ( careful could be hot)
Then feel where it returns., if cooler then a blockage could be identified. Then repeat process on gas and you may note the pipe work is hot all the way round.
This is because gas can produce more power and push through the blockage.

There is a cheaper solution to repairing, which is to remove the fridge and shake and turn upside down.. (check you YouTube). This can resolve but generally always comes back at some point.

Good luck

Update

Left it on Gas for 2 hours . Fridge and freezer dropped to correct temp according to the little fridge thermometers I used. Switch over to mains and left it for 6 hours and the temp dropped off and after 8 hours back to warm. Temp of the flue pipe at the back very hot , too hot to touch , so the 230v element is working so can I assume the electronic brick /PCB is working?

I like the idea at taking it out and turning it upside down but not sure it's that practical as its unit is 54KG and I don't think there is the space to do it. Also how would you even get it out of the van as it looks to be wider than the hab door

 

[Lenny HB]

Also how would you even get it out of the van as it looks to be wider than the hab door

If your hab door is the wider 60cm one it will go through if you remove the flyscreen and the door catches on the frame. Otherwise it would be a windscreen out job. Same would apply if replacing the fridge.

 

[Pete and Liz]

Update
Dometic replaced with Thetford compressor fridge. I kept the Dometic oven , just removed it from the tech tower and put it on a shelf above the fridge. The guys at Autogas 2000 repiped the oven for me and the final part was to block off the extra vents with the artic covers.
The fridge draws about 3.1A with on max and warm unit it reaches temp and the very little (0.4-0.7A) on keeping it at temp. As we have a 300Ah battery 375W of solar and a 50A B2B I don't think we will be having a problem. Overall not a bad job but it would have been better with two people for the removal of the old fridge and the lifting in of the old.

 

[haganap]

Forgot to update on mine.

All fixed, cooiling unit changed and works again.

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[StillGoing]

Update
Dometic replaced with Thetford compressor fridge. I kept the Dometic oven , just removed it from the tech tower and put it on a shelf above the fridge. The guys at Autogas 2000 repiped the oven for me and the final part was to block off the extra vents with the artic covers.
The fridge draws about 3.1A with on max and warm unit it reaches temp and the very little (0.4-0.7A) on keeping it at temp. As we have a 300Ah battery 375W of solar and a 50A B2B I don't think we will be having a problem. Overall not a bad job but it would have been better with two people for the removal of the old fridge and the lifting in of the old.



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I replaced my RMD 8505 with a Thetford T2160 after my Dometic failed similar to yours. I’m impressed that you did it on your own! I couldn’t have done it without help lifting the old unit out and lifting the new unit in. Respect!