# Fridge frame heater



## ceejayt (Nov 25, 2005)

So, hopped off the ferry today to find our fridge dead as a dodo. we went to the local service centre who did a great job and fixed it but left me a bit puzzled.

Our fridge freezer is a Dometic RMD5505 - it has a frame heater which we have never used that apparently evaporates condensation from the freezer frame. The problem with the fridge was that water had got into the switch on the fridge which is a circuit board and blown another fuse on a circuit board behind the fridge (accessed from outside). 

Apparently, in warm weather one should switch on this frame heater as it stops this happening and he said keep it on all the time. However, reading the manual the frame heater when switched on only stays on for two hours anyway. So, should we turn it on every day or what?

Quite mysterious and sounds more like a design fault really.

Anyone any thoughts?


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## Ozzyjohn (Sep 3, 2007)

Our fridge is the Dometic 7655L - it too has the frame heater. I'd almost forgotten about the feature - though we did use it briefly when we first had the motorhome a couple of years ago - it did effectively chase away the visible condensation on the fridge frame in the area between the fridge and freezer doors. Haven't been anywhere so consistently warm since to prompt me to use it again. 

Reading our Dethleffs manual it contains a warning, "If the frame heater is switched on, it will always consume current. Therefore, switch off the frame heater if the vehicle engine is off and the vehicle is not connected to the 240 V power supply." It goes on to say that the frame heater should be used if the temperature and humidity are high to prevent corrosion. 

Current Dometic website states that the purpose of the frame heater is to prevent the freezer door from sticking.

So, as you've probably guessed, I'm no expert on this subject. At least the timer yours has seems to be a step towards avoiding unexpected battery drain. I must check to see if ours is drawing current from leisure or vehicle battery.


Regards,
John


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## ceejayt (Nov 25, 2005)

Interesting re the comment on 230v or engine on as when we used it we did notice a significant ensure battery drain as we weren't on EHU. 

Will keep that in mind 

Thanks


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## voyagerstan (Aug 6, 2010)

could you tell me where abouts the switch is . ihave a switch on the underside of the freezer compartment frame and ihave no idea what its for ? :?: :?:


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## Ozzyjohn (Sep 3, 2007)

Hi,

The switch on ours is next to the energy source selection dial. It is a push button switch with a red light next to it. Neither switch nor light has any identifying mark or label.


Regards,
John


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## ceejayt (Nov 25, 2005)

Ours has a switch next to the energy selection and has a picture that looks like heater. It then lights up an led to say it is on


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## Ozzyjohn (Sep 3, 2007)

Hmm, my memory isn't what it used to be. Our switch also has a heater symbol next to it, contrary to my earlier assertion. 

From the Dometic handbook, it would seem that the current draw is 3.5 amps.


Regards,
John


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## teemyob (Nov 22, 2005)

*Use*

Hello,

The frame heater is what is know as an "Anti Condensation Heater" Some people call it a "Mullion heater".

*Keep it on as much as possible*

Our is on all the time we have it in-use.

Failure to do so will lead to condensate forming on the inside of the Separator shelf and insulation. This in-turn leads to moisture ingress into the insulation and as mentioned, the electrics. Causing further problems.

Moisture will collect on the inside where you can't see it. It well then leak and impregnate the insulation. This makes the appliance less efficient too.

On most Domestic Refrigeration appliances, the Anti Condensation heater is an "Anti Condensation Coil". The heat is provided by taking a loop from the compressor discharge and forming around the inside the door frame as part of the condensor. This simply uses waste heat from the refrigeration cycle to keep the seals and frame warm.

TM


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## Ozzyjohn (Sep 3, 2007)

*Re: Use*



teemyob said:


> This simply uses waste heat from the refrigeration cycle to keep the seals and frame warm.


Hi,

Keeping it on all the time makes perfect sense - indeed if it used waste heat then the manufacturers needn't have bothered to fit a switch? Using a separately powered electrical element (with a not insignificant current draw) seems like a somewhat sub-optimal piece of design. Presumably done on cost grounds - that will have helped to make these fridges so cheap... :?

Regards,
John


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## teemyob (Nov 22, 2005)

*Re: Use*



Ozzyjohn said:


> teemyob said:
> 
> 
> > This simply uses waste heat from the refrigeration cycle to keep the seals and frame warm.
> ...


You can make a loop condensate heater from an absorption system. But....

The Absorption system works on, temperature to make the Ammonia rise and gravity fall. So the loop is difficult to build into the circuit as it would be below and cause a kind of lock.

I dare say it is possible, but then there would be no way of controlling the temperature of that part of the circuit and it could get so hot it could melt or injure the user.

Domestic or Compressor refrigeration is pumped. So it is possible. And easier to design so as to not get so hot.

TM


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## Sheeds (Apr 8, 2011)

I just wish the whole 12V electrical system would be OFF when the main control switch was turned OFF. Nothing at all should be able to be turned on! Wiring in one Australian Motorhome leaves "live" current to the fridge heater, any diesel space heater, outside awning light and 12V electric step. I understand this "sytem design" is a copy of a European setup. Forget to turn them off,particularly the fridge heater,and you come back to a flat battery. I say such a system is unsatisfactory and the Australian Motorhome manufacturer has no satisfactory answer. I just like absolutely everything to be OFF when the Motorhome is to be vacated for some time.


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## teemyob (Nov 22, 2005)

Sheeds said:


> I just wish the whole 12V electrical system would be OFF when the main control switch was turned OFF. Nothing at all should be able to be turned on! Wiring in one Australian Motorhome leaves "live" current to the fridge heater, any diesel space heater, outside awning light and 12V electric step. I understand this "sytem design" is a copy of a European setup. Forget to turn them off,particularly the fridge heater,and you come back to a flat battery. I say such a system is unsatisfactory and the Australian Motorhome manufacturer has no satisfactory answer. I just like absolutely everything to be OFF when the Motorhome is to be vacated for some time.


I understand your point and agree.

Solution: Fit an Isolator Switch to the Battery(ies)

Inexpensive and Simple.

Like this

or

Maybe this?

TM


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## voyagerstan (Aug 6, 2010)

*climate control*

i have had my fridge about 5 years just noticed this switch a couple days ago (it is tucked away under main switch panel and marked climate control ). anyway turned on last night this morning bateries flat as fluke ! so not be doing that again . :evil: :evil:


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