Fridge 12 volt intermittent

[Darren_5078134]

I have just bought my first van a 2001 sterling europa and but with the engine running and the fridge switched to 12v it lights for a while and goes out,until two relays click in as it cools,it then works for a few seconds and then it starts again.On 240v everything seems ok.

Can anyone shed some light please Darren

 

[rayc]

Darren, can you confirm that with the engine not running that the 12v lights work in the van? When you start the engine confirm that the lights go out and that when the fridge 'turns off' whether the lights come back on or not.

This may all sound strange but I am trying to establish if the fridge supply on pins 6 (+) and pins 7 (-) is constantly present when the engine is running.

 

[Darren_5078134]

hi ray with the lights on, if i start the engine they go out,if i then switch on the fridge it works for a while, i hear a relay click the fride switches off, and the lights come back on.

i have battery +4 and -3,-7 and +12v at 6 with engine running, i have changed the grey socket on the van,and checked all the earths on the car,could the fridge be drawing to much power sausing the relays to overheat and cut in and out

cheers Darren

 

[rayc]

Darren, I think the problem is in the car. It is either the relay circuit which switches the fridge supply through on pin 6 when the engine is running, or a poor connection to earth on the 12S pin 7 ( black wire).

Can you do a simple test and connect a battery with the + to pin 6 of the van 12S ( via a 15 or 20 A fuse) with the - to pin 7. Does the fridge stay on? A fully charged car or leisure battery would run the fridge for a few hours or so. If it is ok this confirms it is the car.

What I think is happening is that the fridge supply from the car, that is pin 6 and 7, has a high resistance in it. When you first start the engine the voltage is present which operates the habitation relay in the van, (the reason the lights go out), but when the fridge starts to draw current the voltage on pin 6 or 7 fails which drops the relay out which starts the action all over again.

 

[rayc]

Darren, I think the problem is in the car. It is either the relay circuit which switches the fridge supply through on pin 6 when the engine is running, or a poor connection to earth on the 12S pin 7 ( black wire).

Can you do a simple test and connect a battery with the + to pin 6 of the van 12S ( via a 15 or 20 A fuse) with the - to pin 7. Does the fridge stay on? A fully charged car or leisure battery would run the fridge for a few hours or so. If it is ok this confirms it is the car.

What I think is happening is that the fridge supply from the car, that is pin 6 and 7, has a high resistance in it. When you first start the engine the voltage is present which operates the habitation relay in the van, (the reason the lights go out), but when the fridge starts to draw current the voltage on pin 6 or 7 fails which drops the relay out which starts the action all over again.

Darren, another test you could do is: without the caravan attached monitor the voltage on the car 12S pins 6 & 7 (engine running). Put a load across the meter e.g a spare headlight bulb and confirm whether the voltage remains constant or not.

 

[Darren_5078134]

Darren, I think the problem is in the car. It is either the relay circuit which switches the fridge supply through on pin 6 when the engine is running, or a poor connection to earth on the 12S pin 7 ( black wire).

Can you do a simple test and connect a battery with the + to pin 6 of the van 12S ( via a 15 or 20 A fuse) with the - to pin 7. Does the fridge stay on? A fully charged car or leisure battery would run the fridge for a few hours or so. If it is ok this confirms it is the car.

What I think is happening is that the fridge supply from the car, that is pin 6 and 7, has a high resistance in it. When you first start the engine the voltage is present which operates the habitation relay in the van, (the reason the lights go out), but when the fridge starts to draw current the voltage on pin 6 or 7 fails which drops the relay out which starts the action all over again.

cheers ray tried the test with the battery found out as you said it is a problem with the car, it seems to be the battery feed

cheers Darren

 

[Petemate]

Rayc - if you are still around (the post was quite old but I researched and found it for my problem) I would like to thank you for the hints.
Like Darren, my outfit was playing up. Symptoms, similar to Darren's, were: upon switching on the fridge 12v following connecting up, the light came on OK but as I was in a hurry to depart the first time of using our new (to us) caravan, I just assumed all was in order. Well, that was last June, and a couple of trips later I noticed that after about 5 seconds the light went off again and two seconds later it came on. Relay clicks off & on. So I thought I would 'get round' to checking it. This year first two trips the same, then yesterday set off to come home after our third trip away and no light. Quick check fuses - all in order. Stopped after an hour and a half for our lunch, and it started to work when we started to continue home, but still intermittent. So I decided to do some research and came up with your very helpful replies/advice.
Just before our evening meal today, I followed your tips and got as far as checking the output from the car (which I knew was OK from using out previous 'van but went through the motions anyway). I got 13.6V and with a 65w halogen headlight bulb on load, it only dropped a bit, to 12.9V. Now we both know that it only takes a smidgeon of voltage to activate a relay, so my money was on that just as 'er indoors called me in to eat. Eagerly, I returned to the task in hand, popped in a spare new old stock relay and voila! All working as it should. Over the next few days I will unclip the relay cover and I expect to find corroded contacts, which will be cleaned up to provide me with a spare. Interestingly, the resistance appears to be the same on both relays so my money is on the contacts.
Thanks again, and I hope the foregoing is of use to other contributors.
Pete

Edited to add: contacts were corroded just enough to prevent continuous running. Cleaned up and now stood by as spare. I suspect that the previous owner may have not pre-cooled via mains overnight before setting off. Of course this is not always possible, esp when caravans are in storage, but popping a few ice packs in the freezer compartment overnight can be a great help to the poor old 12V!!
Pete