I think your fridge can run off the car when driving, keeps it at a constant temp, does not make it get any colder, when at a campsite you have to run it off mains or if its a 3 way one gas.
that's the way my motorhome one works, best to plug it in for a night to the mains at home before you go away so that it is cold before you set off.
tho on my splitty with a compressor fridge , I run it using 2 leisure batteries thro the night , recharge and running thro the day via 2 x 100 watt solar panels.
as said need model of fridge
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