Caravan fridge 12v not working?

I have an Electrolux RM4270 fridge in a 8 yr. old caravan we have had from new. It works on mains and gas but not on 12v.
The red neon glows when the car engine is running but the fridge does not chill.
In a service the engineer pulled the fridge out and got the neon working but I don't think that the 12v cooling was fixed.