my fridge works on 12v with the engine running as i can see the red light illuminated on the switch, but you can tell its been off during travel as the fridge warms up and the light is often off after driving a while, indicating intermitent power.
it did this only old car also so i think the car is ok and must be caravan side.
any ideas of the cause and the easy things to check first before contacting a repairer ?

toyota rav4 diesel, i know about cooling it down first and the 12 v maintains the coolness etc, but surely the red light switch should be illuminated constantly ?
i run dometic rc1200 in the boot off 12v and it works perfectly off a 12v cig lighter socket

This does sound like a smart alternator turning off after the battery has been topped up after starting. There's a discussion here

https://www.caravanclub.co.uk/club-toget...technology-etc/

Steve

thanks Colin, even with perfect operation it sounds like i maybe flogging a mediocre horse here !
ill look into combicool it sounds a better fix for cooling on the move

The cool box will be a compressor unit, like your fridge at home. The Eriba units are absorption types, a different modus operandi.
If your towbar has model specific wiring and software it should turn off the car's alternator energy saving system, so that it supplies power whenever it's running. Cheaper non specific wiring doesn't do that and the alternator stops producing power once the car battery is replenished.
One trick worth trying is to switch on the headlights and that drain prompts the alternator to produce power which then feeds the caravan fridge and charges the caravan battery.

its a 2002 model, the 12v power is intermittent so the relay is prob ok

You haven't mentioned tache RAV4 's model year, or whether it has model specific towbar wiring or the simpler generic relay. The former will, among other things, stop the alternator from cutting out.
Whichever wiring it has, running with headlights on should make the alternator work all the time and therefore power the fridge and the red light all the time.

its a 65 plate business edition, its not toyota wiring, third party wiring that was newly fitted 2 years ago im not sure of the make.
we are away soon so ill switch it on and if the light is out when we arrive ill switch the lights on to see if it starts working hopefuly proving or disproving the theory

thanks for the help everyone

Good luck.

All towbar wiring tends to be third party, unless factory fitted. Model specific is as the name implies, designed for a particular car and is programed with Toyota software to operate all the Toyota towing features, like turning off rear parking sensors and displaying the car and caravan in the display. The cheaper generic wiring just uses a standard relay to cut in the power to the caravan and if the alternator decides to stop making power it can't make it desist.

I ordered a factory fit towbar with my Seat Ateca (2017) and was unsure if the smart alternator would be defeated when towing. To check this I plugged a voltmeter in to the 12Vdc socket and went for a drive. When not towing the voltage went below 12V frequently. When towing the voltage remained steady at about 14V.
Battery charging and 12Vdc fridge operation therefore work OK.

It was only recently that I noticed that when towing, the diagram on the screen changes from just a car, to the outline of a car and caravan.