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No Fridge Output On My Grey Socket


Barry J
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Recently I've noticed that my fridge isn't running when the car is plugged into the van.

 

I've measured the fridge output (red) at 2 o/c position on the grey socket and am getting nothing - the supply to caravan lights (green) at 6 o/c position and reversing light is working fine.

 

The Witter towbar was professionally fitted when the car (2007 Kia Sportage) was new and it has worked with the fridge in the past.

 

I had a quick look at the car fuse boxes (3 of them) to see if there were any dedicated fuses for extension lighting or the towbar, but nothing is marked/obvious.

 

Does anybody know how these bars are normally wired into the car ??

 

Where does the towbar fitter take the power from ?

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Hi Barry,was your tow bar fitted by your dealership ? If so it has been found on this forum that most dealerships don't connect this part of the electrics. You might have to take it to a tow bar fitting specialist to get this sorted.

 

Doosan

 

Bailey Pageant Series 6 Champagne 2007    Tow Car Toyota Rav4

 

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No, it was fitted by a towbar/towing specialist shop. It worked fine until recently and I suspect a blown fuse or corroded connection.

 

its just a question of tracing the fuse in the car.

 

Hi Barry,was your tow bar fitted by your dealership ? If so it has been found on this forum that most dealerships don't connect this part of the electrics. You might have to take it to a tow bar fitting specialist to get this sorted.

 

Doosan

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All readings were taken in three states; engine off, ignition off and engine running.

 

The green supply varied as expected (difference between battery open circuit voltage, on load with ignition on and alternator output when engine running - the fridge output was zero in all three states.

 

Barry

 

Did you test the outputs from the 12S with the vehicle's engine running ?

 

DeeTee

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Hi Barry,

I had a similar problem earlier this year. I used a meter to test the grey socket on the car with the engine running and got nothing!

The relay unit for the 12s had stopped working. I took it back to the towbar fitter an got a new one installed. Cost £20.

 

Hope this helps.

 

Cheers, Andrew.

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Depends a little bit on the car as the feed for the fridge/battery charge may be in the loom. If so the fuse should be listed in the fuse box cover and in the handbook.

 

However due to the high (20A+) current it is quite common for these circuits to be installed from scratch and not be part of the car loom. If done correctly this would involve at least one if not two heavy-ish cables being fed directly from the battery this/these should then feed two separate fuses, one for the battery charge directly connected to the green circuit and the other via a relay to the red circuit. In order to stop the battery in the van being a current source when starting the car there should be a blocking diode in the green cct and in some cases I have seen this as part of the relay module as well.

 

The 1st clue is to look at the battery +ve terminal for additional cabling and as it is preferable to fuse at this end this cable may lead to a pair of fuseholders. The relay only allows the fridge feed to go live once the engine is running and again it is far from unusual for this relay to fail. Wheras the fuse is preferably at the battery end the relay module is more often at the back near the hitch.

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Hi Barry,

I had a similar problem earlier this year. I used a meter to test the grey socket on the car with the engine running and got nothing!

The relay unit for the 12s had stopped working. I took it back to the towbar fitter an got a new one installed. Cost £20.

 

 

 

 

I recently had a similar problem when I had the car rewired for 13 pin. There was output at the pin but the blue light on the fridge was still flashing. Turned out it was caused by voltage drop from a defective car relay - Thetford fridges will detect low voltage as if no power at all.

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The feed for the fridge is fed by the alternator through a relay.

 

It will only show a voltage at the 12s red wire if the revs are ok. If this is not the case then the relay will prevent a feed.

 

Either the relay is failing, the revs are to slow or the alternator is not providing a feed.

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As the 12v output from the alternator is directly connected to the battery it cannot be stated that the alternator feeds the fridge not the battery.

 

The fridge feed is only supposed to be live when the alternator is generating output but this is the purpose of the relay. How this is done depends on the installation but there are two basic systems.

 

The simplest one is the voltage sensing relay, this reads the input voltage and when below a set threshold wil not energise but when the voltage is high enough will operate. This depends on the fact that the off charge voltage of a car battery (12. 6v) is lower than the charging voltage of the alternator (14. 4volts) so when the engine stops and the voltage falls the relay will drop. You have to be a little careful when testing this type of circuit because with no load the voltage does not drop immediately so the red cct may stay live for a short while, not such a problem with modern cars with so much electronics which do not turn off as soon as you turn off the key.

 

The other and more accurate type taps in to the charge indicator signal coming from the alternator. This is the drive for the dashboard charge failure light which normally goes out when the engine has been started. When the output from the alternator is sufficient to start charging the battery the light goes out and the relay for the hitch energises to drive the fridge. However with modern cars this light is frequently actually driven by the cars inbuilt computer and no longer directly by the alternator. This makes it harder to tap in to to get the signal. Due to this the voltage sense system is becoming more common.

 

Essentially both circuits get their supply from the battery, just one is switched the other is not.

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