# Constant buzzing on 12volts



## Tansy (May 11, 2005)

Hi all,
Dometic RM78605L.
Have just returned from a weekend away, and whilst all was well the first day, on the second, a buzzing started from behind the control panel whilst driving. This happens both when the engine is going and the 12v switch is manually selected or when AES is selected. Anyone had experience of this, and if so what is the cause/remedy?

Many thanks


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## cabby (May 14, 2005)

It will be either a loose connection or a faulty unit.

cabby


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## Patrick_Phillips (Aug 17, 2006)

A loose connection will normally be uneven in frequency. It might be worth checking any screw terminals there may be.
The other causes of consistent buzzing are transformers and relays.
Both are fairly easy to diagnose by getting a wooden or other non-conductive stick and touching any transformers or relay covers and you will probably fee the guilty party vibrating.
A transformer often buzzes because the steel laminations have come loose but they are associated with AC current, of course, so probably not the culprit here.
That leaves us looking at relays. most common causes are poor circuit design where the relay chatters on the threshold of a change of state. Unlikely in this case due to the quantity produced.
So we come down to dirty contacts on a relay.
Most small relays are boxed around the contacts. But nevertheless, it may be worth getting some switch cleaner (Maplins or any electrical wholesaler) and spray it about a bit. It may cure the problem but I don't give guarantees!!!

Patrick


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## uncleswede (Apr 16, 2010)

We had exactly this issue with our RM76xx Dometic fridge. It's a low voltage alarm which, in our case, was due to old, corroded connections rather than a component failure. 

The only person we found who knew what he was talking about was Peter Hambilton at Preston (but he is a Hymer specialist...). He dismantled and cleaned the connections and all has been fine since then.


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## Geriatricbackpacker (Aug 21, 2012)

Had this with my elektroblock and it was a blown fuse and the buzzer was warning that the leisure batteries were not charging. Fuses all looked ok but when I eventually found the defective one it had cracked across one the bayonet blades and still looked intact at first glance. Replaced fuse and the annoying noise stopped...if I could just find the same one on the wife. :lol:


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## dalspa (Jul 1, 2008)

I had this happen a couple of years ago - had to turn off the auto 12v supply switch on the AES to get rid of the loud buzz, in order to continue journey home. The 12v feed for the fridge comes from the vehicle battery (in our case under the floor in the cab area) so as only to work with the engine running. There were two fuses side by side near the battery and one of them had burnt out along with the fuse holder. Fitted a new holder and fuse, then checked to see what may have caused the problem. Took the fridge lower external vent cover off and checked the heavy duty 12v feed and found the wire was loose in a connector block - so probably caused heat build up in the wire. May have been never tightened up from new/build! Checked all other connections while I was at it. Only cost a few pounds to sort out. Fridge has worked perfectly since.
DavidL


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## Tansy (May 11, 2005)

Hi, thanks to all respondents. I have checked as far as possible, without dismantling the fridge, all connections which are tight, so I can only assume that some unit must be faulty. Does anyone know how to gain access to the control panel? There are 3 screws on the black bit behind the panel, but when I undid them, the piece that looked as though it would come off, didn't. I don't want tyo exert too much force in case the plastic breaks!!


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