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CliveB

Checking Fridge Operation

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Posted (edited)

New to "modern" i.e. 13 pin electrics.

On a recent 8 hour return trip the fridge defrosted. It was set to 12v on the control.

Before getting out the multimeter I have been reading on latest wiring (caravan and car handbooks not much use).

As I understand:

The fridge is powered via pin 10 which is live only with the engine running.

Pin 9 is permanently live, powers the ATC,  and charges the leisure battery (but only when pin 9 is live).

Is this correct?

In the caravan there is a 12v fuse labelled "fridge" which I will remove and check.

The 13 pin loom seems to termiate under the passenger seat of the car.  There are a number of electronic black boxes plus a bank of 3 fuses (15a and 20a). Suggestions as to what circuits these protect.

Am I also correct in assuming that the alternator on my euro 6 diesel may cease charging when the car battery is fully charged?

Information overload!

Edited by CliveB

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A quick simple test is to turn on the awning light (with car hooked up). Then start the car. When you start the car, and rev it gently, the awning light should go off. 

Re you car wiring. It would help if you told us the make / model / age. That way people with knowledge of your car maybe able to offer detailed advice 

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8 minutes ago, CliveB said:

Pin 9 is permanently live, powers the ATC,  and charges the leisure battery (but only when pin 9 is live).

Is this correct?

 

I guess Pin 9 would be permanently live, when its live.

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I think OP meant "but only when pin 10 is live".

The only way of locating the problem is to get out the multimeter - start by checking whether pin 10 is live on the car tow socket with the engine running, this will isolate the problem to either car or caravan.

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22 minutes ago, onewheelonmywagon said:

The only way of locating the problem is to get out the multimeter - start by checking whether pin 10 is live on the car tow socket with the engine running, this will isolate the problem to either car or caravan.

Not forgetting that the fridge circuit has its own specific earth connection.

Check voltage between pins 10 and 11

 

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First hook up the 'van, switch the fridge to 12 volt and run the engine just above tickover. If the light isn't  on, you've a fault! 

 

Then check the 12v feed from the alternator (when the engine is running) and the 12 volt permanent feed which powers up the circuit board in the fridge.  If one is missing check your hook up and fuses.

If these are both there then there's a common fault with Dometic fridges ( you've not said what type but I'm assuming) in which the circuit board goes faulty on 12 volt working. (works OK on 240v & gas)!

 

There's an easy('ish) fix ( doc attached from the original post) where you short out the thermostat circuit on the 12 V side ( it's not actually used anyway) by wiring a fuse across the correct terminals ( the fuse is for protection of the rest of the cct ). This "cure" works a treat and saves buying a £110++ new circuit board. I ran my Avocette wit this repair for 3 years and no problems at all. My service engineer OK'd this repair as completely safe.

 

Cheers

 

Jim 

 

 

caravan fridge fault repair .doc

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1 hour ago, JamesF said:

First hook up the 'van, switch the fridge to 12 volt and run the engine just above tickover. If the light isn't  on, you've a fault!

Unfortunately this Domestic fridge does not have a light to indicate when the 12v supply is active. Would have helped.

The car is a 2 year old VW Caravelle with a dealer fitted Westfalia towbar and electrics. I requested full connections to the 13 pin socket.

Caravan a 2018 Bailey Pegasus.

Caravan in storage which makes things a little difficult.

As suggested will firstly check voltage across pins 10 and 11.

Difficult to connect in storage, but am I correct in assuming there should be a resistance of around 1 ohm across 10 and 11 on the caravan plug with the switch set to 12v?

 

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Posted (edited)

If you haven't seen them already these guides from Flying Tog may be helpful

 

Caravan Chronicles

 

 

Edited by onewheelonmywagon

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17 minutes ago, onewheelonmywagon said:

If you haven't seen them already these guides from Flying Tog may be helpful

  

Caravan Chronicles

Many thanks.  I had not seen these guides.  I think I now understand the electrics, particularly with regard to the fridge.

As I see it I should be able to determine if the car fridge supply is operational by measuring the voltage across pins 10 & 11 on the socket with the engine running, and the the fridge circuit is intact by measuring resistance across pins 10 & 11 on the plug with 12v selected on the fridge panel.

What can possibly go wrong..?

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Checking ohms across Pins 10 & 11 on the caravan plug will only measure the habitation relay resistance. You need to measure ohms across the fridge12v heating element.

You can use the fridge 12 v fuse to help with this - remove the fuse and put one multimeter probe on the fridge side of the fuse and the other probe on the Pin 11 connection in the van. If you can't access the Pin 11 connection in the van you will need a long test lead to get back to the caravan towing plug.

The heating element should be about 170 watts  so amps will be 170/12 = 14

Resistance will be volts/amps = 12/14, which is just under 1 ohm.

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9 hours ago, CliveB said:

What can possibly go wrong..?

 

The Habitation relay is effectively operated by the Fridge supply, so you will be measuring the resistance of the relay coil. You may notice a difference in resistance with the fridge on/off but may not be conclusive.

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Many thanks.

So the fridge is normally operated through the habitation relay and not directly from pin 10 as shown in the schematic in the caravan chronicles link?

 

Screenshot_20190720-093037.png

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Posted (edited)

I got me knickers in a twist.

The fridge is supplied directly from the car with the engine running via Pin 10.

Measuring resistance across pins 10 and 11 on the disconnected caravan plug will show a combined resistance of the habitation relay and the fridge.

 

car-caravan-relays-02.jpg

Edited by onewheelonmywagon

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14 minutes ago, onewheelonmywagon said:

Post deleted. I got me knickers in a twist.

car-caravan-relays-02.jpg

Thanks - a little more detail. But again shows +ve feed to the fridge not passing through the habitation relay?

 

 

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I edited my post just now to agree with you - the power supply goes directly via Pin 10 to the fridge and not through the habitation relay. Measuring resistance across pins 10 and 11 on the disconnected caravan plug will show a combined resistance of the habitation relay and the fridge.

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Habitation relay (coil) is in parallel with the fridge.

So power does not go "through" the relay to the fridge.

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OP. I would measure voltage between 10 and 11 at the car socket. That will tell you if the van has the full wiring. 

Next do the awning light test as above that tells you the relays are doing their thing.

I would then remove the fridge vents and measure the voltage where at the 12v plug that comes from the van wiring and joins the fridge. This will usually be a thick wire. I bet here you will see sub 10v.

The issue with modern fridges is that they draw so much power, most car wiring is only 2.5mm and with voltage drop especially along a long vehicle like yours there isn't enough umph to power the fridge element.

I posted here a while back how I had to rewire my 12v pos and negative for the charging circuit with a split load relay straight from the battery with thicker wire. Easy on my truck that doesn't have complicated canbus to worry about. Yes some smart alternators also reduce output 

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Jiffy

Many thanks for these suggestions.

I know understand why switching on awning light will verify that pin 10 is live when the engine is running.

Agree hitching up and removing vent to check voltage is the best option, but this would be difficult in storage.

Will start with the 13 pin socket on the car.

 

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1 hour ago, CliveB said:

Jiffy

Many thanks for these suggestions.

I know understand why switching on awning light will verify that pin 10 is live when the engine is running.

Agree hitching up and removing vent to check voltage is the best option, but this would be difficult in storage.

Will start with the 13 pin socket on the car.

Might also be worth taking some help with you and getting then to hold the car revs above idle and seeing if this helps. My experience at best is that the fridge might stay a bit cool but I wouldn't rely on it to keep food frozen. Most use a frozen bottle of water to help keep it cool.

1 hour ago, CliveB said:

 

 

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One other related question.

If in addition to powering the fridge the switched pin 10 function is to operate the habitation relay which isolates the caravan 12v to ensure no interference with the car electronics this is a "must have" connection and should not be omitted?

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A lot of German cars with factory towbars don't have power on pin 10.

This is not a major issue but bear in mind that your van battery won't get any charge from the car. Obviously the fridge won't work on 12 volts either! My car is wired (or not wired!!)  like this and I don't worry about it.  Food goes in the fridge chilled. Don't take frozen. On the rare occasion that the van is at the house before going away, the fridge gets chilled on mains and it stays cool for the journeys I do. I don't do Continental touring where a cool fridge may be needed more.

Battery has, so far, always had enough in it to drive the mover into storage - I could reverse it in with the car, but its easier on the button!

 

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3 hours ago, AlwynMike said:

A lot of German cars with factory towbars don't have power on pin 10

I suspect this is the case with my VW but still haven't checked.

I have a solar panel so battery always topped up.

Like you I could live with no 12v fridge connection, but would be a little annoyed as it was something I did specify with the dealer.

At least all lights and ATC fully functional.

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22 minutes ago, CliveB said:

I suspect this is the case with my VW but still haven't checked.

I have a solar panel so battery always topped up.

Like you I could live with no 12v fridge connection, but would be a little annoyed as it was something I did specify with the dealer.

At least all lights and ATC fully functional.

 

Recent VW Group vehicles have full wiring with factory-fit towbars.

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30 minutes ago, Black Grouse said:

Recent VW Group vehicles have full wiring with factory-fit towbars

Mine was VW/Westfalia kit but fitted by the dealer.

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Feedback to those kind people offering advice.

Tested pins 10&11 today with engine running.  A healthy 14.2v on my DIY meter.

Also a constant voltage at pin 9 (which I was confident about as the ATC kicks in as soon as a connection is made).

Hoping to get out to the caravan later this week.

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