Fridge not running on 12volt

Aug 2, 2010
175
130
TONYPANDY Rhondda Wales
Funster No
12,986
MH
Auto-Trail Cheyenne 660
Exp
Since 2009
Hi my fridge will not work on 12volt only makes a buzzing noise. Runs great on 240 and gas any idea’ s please thanks Robert
 
Dec 21, 2011
3,372
2,778
London
Funster No
19,230
MH
IH PVC
Exp
Since 2012
As above. 12v usually only works with the engine running
 

pappajohn

LIFE MEMBER
Aug 26, 2007
36,081
24,130
Dark side of the moon
Funster No
172
Exp
Since 2005
Engine running and fridge will not work only a buzzing noise from fridge
How do you know it's not working.
In 12v operation there is very little heat from the vent, if any, and no noise at all.
12v will not cool the fridge, it will only maintain a temperature already present from gas or 230v.
 
Jan 28, 2008
5,778
5,782
walthamstow east london
Funster No
1,353
MH
renault burstner delphin
Exp
7 years campers before that
you need to find out if theres a 12v supply to the fridge when the engine is running if theres not it could be the relay
 
OP
RobGriff
Aug 2, 2010
175
130
TONYPANDY Rhondda Wales
Funster No
12,986
MH
Auto-Trail Cheyenne 660
Exp
Since 2009
Hi Steve thought it might be the relay ,going to have a look tomorrow after work . Hope you and Diane are keeping well . Rob and Deb
 
Nov 7, 2015
296
163
Shropshire
Funster No
40,071
MH
Autosleeper Broadway
Exp
since 2015 previously caravaning 25 years
Can't help with the noise but when our Thetford fridge stopped working on 12 volts it was due to a bad electrical connection at the plug and socket found at the rear of the fridge at floor level in our case easily accessible from the lower vent cover, pull the connector apart and look for a burnt connection.
 
Jan 28, 2008
5,778
5,782
walthamstow east london
Funster No
1,353
MH
renault burstner delphin
Exp
7 years campers before that
actually the buzzing does point towards a relay not holding follow the buzzing noise to locate it mine is behind the fridge
 
Dec 12, 2010
2,860
5,068
Cumbria
Funster No
14,651
MH
C Class
Exp
since 2011
I've just recently deleted the couple of pics on my phone that I took of the 12 volt electrical connections on the rear of my Dometic and I seem to remember seeing an automotive relay in amongst it all. If that's playing up, it will make a buzzing noise. Usual reasons for it to buzz are low voltage supply to the coil or a bad connection. I've had to replace a couple of corroded Lucar connectors on mine.
 
Apr 27, 2016
1,007
458
Manchester
Funster No
42,762
MH
A class Hymer
Exp
Since the 80s
There are two 12V supplies to the fridge. One is a low-current supply to power the control board. The other is a high-current supply (about 14 amps) that powers the heater element that works the cooling.

The low-current one is on all the time. The high-current one is selected by the manual or auto selection. On most British MHs you can not run on 12 volts unless the engine is running, and this is done using a relay.

Has this problem suddenly started after working OK for some time? I ask this because if it's always been like this, or the wiring has been changed or is incorrect, the relay could be wired wrong, so that it switches itself on and off rapidly, making a loud buzzing sound.
 

Taff Thomas

Free Member
Apr 7, 2018
39
14
Deepest Kernow
Funster No
53,218
MH
Don't own one yet
Funnily enough I have this problem on the motorhome I have just bought (second hand.) I will post more detail when I pick it up.
 

Gladys

Free Member
Jul 29, 2018
2
0
Funster No
55,233
We have had our second hand Motorhome for the last 2 and a half years and the fridge has always worked fine whilst we’re travelling on 12v. But the last 2 times we switched over to 12v when setting off, the fridge has made a really bad noise. If we turn it off, the noise stops. Can’t understand why suddenly it has started this really bad noise
 

Gladys

Free Member
Jul 29, 2018
2
0
Funster No
55,233
Hi pappajohn

It’s like a really high pitched screech. It doesn’t make the noise on electric or gas mode, only after we have have switched it to 12v. Pretty sure the noise starts when we start the engine when it’s in 12v mode.

Thanks for your reply.
 

oppy

Free Member
Nov 8, 2014
87
54
Glossop, North Derbyshire
Funster No
34,156
MH
Coach built Lunar
Exp
5 years
At the FFF meet last weekend we had an expert tell us that the fridge would not work on 12v (whilst the engine was running) because the relay was faulty. I found the relay, or rather two relays jammed behind the battery. I now have them in front of me, one is a Hella rated at 20/30V and the other is a Tyco but with no rating on it. Both are 5 pin and both have the same numbers allocated to the pins. So, do you think that both are related to the fridge? Can anyone help this poor numpty ?

Peter
 

pappajohn

LIFE MEMBER
Aug 26, 2007
36,081
24,130
Dark side of the moon
Funster No
172
Exp
Since 2005
At the FFF meet last weekend we had an expert tell us that the fridge would not work on 12v (whilst the engine was running) because the relay was faulty. I found the relay, or rather two relays jammed behind the battery. I now have them in front of me, one is a Hella rated at 20/30V and the other is a Tyco but with no rating on it. Both are 5 pin and both have the same numbers allocated to the pins. So, do you think that both are related to the fridge? Can anyone help this poor numpty ?

Peter
No, one is the fridge, one is the split charge to the leisure battery.
Which one is which can only be determined by tracing the wires or using a multimeter.
 

pappajohn

LIFE MEMBER
Aug 26, 2007
36,081
24,130
Dark side of the moon
Funster No
172
Exp
Since 2005
Hi pappajohn

It’s like a really high pitched screech. It doesn’t make the noise on electric or gas mode, only after we have have switched it to 12v. Pretty sure the noise starts when we start the engine when it’s in 12v mode.

Thanks for your reply.
Sorry Gladys, that's beat me.
Only thing I can think will make a high pitch screech is a slack/worn fan belt under load.
Can't think of anything fridge related.... There are no moving parts on the 12v side of the fridge.
 

oppy

Free Member
Nov 8, 2014
87
54
Glossop, North Derbyshire
Funster No
34,156
MH
Coach built Lunar
Exp
5 years
No, one is the fridge, one is the split charge to the leisure battery.
Which one is which can only be determined by tracing the wires or using a multimeter.
Thanks young fella. I pulled them both out and took them to the dreaded Glossop Caravans and asked the electrician about them, he said that they were both the same, so for £3.50 each I have replaced them both and now have a working fridge. So many thanks

Peter
 

pappajohn

LIFE MEMBER
Aug 26, 2007
36,081
24,130
Dark side of the moon
Funster No
172
Exp
Since 2005
Sorry Peter, should have said they are both the same.... 30amp automotive relays as fitted to millions of cars, vans and trucks.
Only difference being where the output goes... Fridge or battery
 
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