Can I use my car's air conditioning unit to cool a refrigerator in the car? I would remove the evaporator unit from the air conditioner, construct and fit an evaporator coil to the refrigerator box, add an appropriately calibrated switch and thermostat to the circuit to switch the compressor in and out but the rest of the unit would remain in place.
(EDIT FROM ANSWER POST)
The vehicle is a bus, engine at rear, currently no aircon, I have a car air conditioner that I can run off the motor. Fridge would be a permanent install. Could fit a domestic freezer evaporator to the fridge onboard, then plumb it into the car compressor etc. use a thermostat to switch the compressor in and out. I agree may be easier to just fit a dometic RV fridge unit but less fun.