New fridge

[Bikeral77]

I had to bite the bullet and buy a new fridge, when the old RM 4270 gave up the ghost.
I am in the throws of installing it. I have the 240v working fine, and the internal light working on a 12v feed, but I'm having a problem getting the 12v side of of the heater element working. I've got the car connected up to the 12s plug with the engine running but I can't get a voltage reading on the feed wire to the heater element, so that part of it doesn't appear to be working. I've checked the fridge fuse that's fine, increased the engine revs above tickover, but still no voltage and no heat from the element. Am I missing something here ?.
Any advise will be welcomed !.

 

[Damian]

Is the 12s plug actually wired correctly?
Is this a brand new fridge or a second hand one?

 

[Bikeral77]

Yes it's a brand new Dometic RM 5330 fridge. The plug wiring is as it was for my old fridge. I'm getting 12v to the feed wire in the caravan with the engine running, but as soon as I switch the fridge onto 12v, all power is lost, as if something has tripped out. Nothing has tripped in the caravan, all 240v and separate 12v feed to the fridge interior light is working fine.
Thanks by the way for your reply, these things test your stress level somewhat !.

 

[Bikeral77]

According to Dometic service, they said to check the cable size and can the car handle the load. Well the old fridge had the same element and was powered off the same cable. I've worked out that it draws 10amps. Most modern cars will handle that. Is there a relay in the car wiring that might not handle this load.

 

[VicMallows]

From your description it does sound possible that a high resistance has developed somewhere in the 12v feed from the car to the fridge. Are you able to measure the current (if any) in that feed? ... this would start to give a clue. A relay, either in the car or the caravan would be a very likely culprit

Exactly where are you measuring the fridge 12v feed when you say 'all power to the fridge is lost when it is turned on'?

 

[Bikeral77]

Thanks for your input Vic. I'm measuring the voltage on the cable that powered the old fridge. I'm getting 12+v, checking that again at the terminal block attached to the top of the unit. As soon as I turn the switch to 12v operation, the power is lost, as if a trip has activated somewhere in the system. This all when the car engine is on a fast idle. I am about to visit the guy tomorrow, that fitted the tow bar, to see if he can shed any light on the problem. It's all very frustrating as all the other services are working fine, and I just want to get the fridge into position ready for our next trip. The amperage draw I've worked out will be about 10a, which must have been the same for the old fridge, so I can't see why I have a problem. I suppose it will all come right in the end, just hope it won't take too long !.

 

[VicMallows]

Bikeral,
You say you have 12v at the terminal to the fridge when it it is switched off. The problem is that you will still see this voltage on a meter (especially a digital one) even if there is a very high resistance in the circuit. If there is a high resistance, the voltage you see will collapse to zero as soon as you apply a significant load (your fridge 10A heating element). I doubt if anything is 'tripping' ... and then resetting automatically, which you imply.

With the fridge switched ON, I suggest you follow the circuit back towards the car. Is there still 12v at the appropriate pin of the 12S connector? ( MUST be still plugged in .......you will have to work out a way of measuring it with the connector plugged in). Now you should have isolated the problem to either car or van ........and so on.

 

[Dustydog]

Bikeral
Well done for doing the job so far :cheer:
. The 12S earth pins have a habit of corroding and burning out. It will be worth your while checking the earth side of the system from car to caravan and fridge.
The following link may help.
http://www.towitall.co.uk/faq/

 

[Firkle]

Bikeral

Have you tried connecting a dummy load ( say a car headlamp bulb) across the fridge 12 volt supply cable you mention and then measuring the voltage? This should isolate whether the problem is the fridge or the 12 supply from the car and allow you to trace back the wiring until you find the faulty joint or connector.

 

[Bikeral77]

Well the problem is solved. I thank you all that offered advice, every little helps as they say, and whatever our caravan problems are there will be someone on this forum that will point us in the right direction and eventually solve the problem.
So, what was it that stopped my 12v system from working, don't we all look for the extreme before looking at the obvious first. Well I do, perhaps that's my failing.So the gentleman that said is your 12s plug wired right, lead me to open up said plug to check. Yes all was wired right, I wasn't expecting it to be wired wrong, but, the centre pin looked a bit squashed I.e it wanted a screwdriver inserted into the end to splay it slightly, this of coarse gave it a better contact to earth, and bingo I had 14v at the cable end, and 12v at the unit end, and that was with the engine on tickover.
The fridge is now fixed in, 240v on, to test it. It's freezing up nicely. Stress level has dropped to somewhere normal, and we're ready for another trip.
Many thanks again to you all, can't praise you enough, just having you at the end of my iPad is such help. I'm 77 years old, and still learning.

 

[thosoneill]

Well done that man

 

[camel]

Bickerall,
well done mate, and happy touring for the rest of the year,

 

[VicMallows]

Pleased you sorted it! It's a useful reminder that the negative return for the fridge is a separate connection via the 12S connector. The reason that the voltage you were measuring at the fridge terminals fell to zero was of course that both sides were in fact sitting at +12v due to the open fridge return in the connector.

 

[Dustydog]

Well done Bickerall .
Your perseverance paid off.
Now you know why I have done the 12s earth mod for the last 15 years .

 

[Bikeral77]

Cheers Dustydog !