12v Fridge Element

[SteveW]

The facts are as follows:-

The vehicle is 3 months old and the fridge was working OK until returning from Adelaide to Melbourne a week ago. Now, the 240 volt operates and the gas operates. 12V does not function.

My test have been:-

With the fridge wired up correctly, switched to 12V, and the engine idling, the heavy feed wire from the 12V battery to the 12V element is reading 8V. At the same time the feed wire from the alternator (sends the signal to the fridge to say that the engine is running - a function of the RM4605 auto switching Dometic fridge) reads 13V+.

With the two 2 element wires (+ & -) disconnected from the fridge, the ohm meter connected to the + & - wires the reading is 0.0 My suspicion is that the element has shorted out.

[Dot]

Steve, I know this does not apply to you but when we put our fridge in (same as yours) the advice was to use only the 240v & gas connections as the 12v connection was too difficult as it would have meant wiring into the vehicle's wiring system, also I understand that it is more efficient to run on the 240v. But as you know if they know you have too tooed with the bits and bobs then they can refuse the warranty claim... Keep them under pressure.. (the advice was given by a local caravan / motorhome builder)

[SteveW]

I must add, Dot, that the dealer principal suggested that running the 240v element via an inverter was not a bad thing.

[BruceS]

With the two 2 element wires (+ & -) disconnected from the fridge, the ohm meter connected to the + & - wires the reading is 0.0 My suspicion is that the element has shorted out.

Steve can you clarify that line above please?
When the wires are disconnected you then have 2 pairs of wires/contacts.
The "feed" should have 12V or more.
The wires/contacts to the element should ofcourse be 'dead'.
Turn your meter over to check continuity. (touch probes together or not etc)
Now test the element end.......... Does anything happen at all??
Sorry I don't use the right terms!!!
If you do have 12 or 13V on the "live" wires try connecting to something that will use quite a bit of power to run. 12V compressor or even a 12V spotlight or one headlight on highbeam etc.
Work OK or weak power?

[oldtrack123]

[1]With the fridge wired up correctly, switched to 12V, and the engine idling, the heavy feed wire from the 12V battery to the 12V element is reading 8V.
[2]At the same time the feed wire from the alternator (sends the signal to the fridge to say that the engine is running - a function of the RM4605 auto switching Dometic fridge) reads 13V+.

[3]With the two 2 element wires (+ & -) disconnected from the fridge, the ohm meter connected to the + & - wires the reading is 0.0 My suspicion is that the element has shorted out.

Hi Steve
[1]the 8v reading indicates a load on that circuit,
combined with the reading of [3] it indicates a very high current
[3] the reading of ZERO resistance certainly indicates a "dead short"
Yes, the element appears to have shorted, not the usual failure which is open circuit .

What does surprise me is that circuit must not be fused ,as with a short circuit, the correctly rated fuse should have blown
to protect the cables!!

Edit
Following on Admins post
Does your meter have a continuity buzzer
If so switch it to that & see if it buzzes when each test lead is connecter to the ELEMENT
If A ZERO Ohm reading it SHOULD
PeterQ
[A qualified electrician]

[SteveW]

Thanks Peter, I'll have a look at the source of that 12v cable - it is from the vehicle battery and is switched via the alternator feed. I have to pull up the cabin floor battery cover, which is no big deal. There are 3 12v sources: 12v from the house battery to power the control electronics, 12v from somewhere past the alternator to signal that the motor is running, and 12v from the vehicle battery to power the 12v element only while the motor is running. When the 12v signal wire has no current (because the motor is not running) the LPG is switched on.

[oldtrack123]

Thanks Peter, I'll have a look at the source of that 12v cable - it is from the vehicle battery and is switched via the alternator feed. I have to pull up the cabin floor battery cover, which is no big deal. There are 3 12v sources: 12v from the house battery to power the control electronics, 12v from somewhere past the alternator to signal that the motor is running, and 12v from the vehicle battery to power the 12v element only while the motor is running. When the 12v signal wire has no current (because the motor is not running) the LPG is switched on.

Hi Steve
That is the way it all should be but the pos line from the vehicle battery should be fused near the battery to minimize fire risk IF a short occurs
The same with the control circiut pos from the house battery ,fused as close as possible to the battery
Fuse rating to suit either cable rating or load current .
PeterQ

[Craig]

Steve, you are correct with 3 x 12 volt power sources being needed but the 12volt for the element is generally still supplied from the house batteries.
Can you confirm that the fridge is getting the signal that the engine is running and it is trying to start on 12v element?

[oldtrack123]

Steve, you are correct with 3 x 12 volt power sources being needed but the 12volt for the element is generally still supplied from the house batteries.
Can you confirm that the fridge is getting the signal that the engine is running and it is trying to start on 12v element?

Hi
Sorry BUT
Definitely SHOULD NOT BE from the house batteries.
NO 3 way 12v fridge element should be supplied from the HOUSE batteries
Many very good reasons why such is a very bad practise
!!!
PeterQ
[a qualified electrician}

[BruceS]

Probably need to clarify that this discussion revolves around one particular caravan and one particular setup of 12V power to the fridge.

It's more than likely nothing related to most motorhomes.

Thought I'd intervene to nip any off-topic discussion in this topic!