how can I fix dometic 4231 fridge does not cool??

The fact that your fridge works on gas tells me that the system is ok, therefore it should be repairable.
These fridges work from 3 different heat sources. 12v element, 240v element and gas - hence 3 way. I suspect that your 240 element may be faulty and needs replacing, any competent electrician should be able to check the element for you. The 12v element will only work in your Motorhome when the engine of the vehicle is running because it draws a lot of current and would flatten the battery in a very short time. The 12v element is not as powerful as the 240v one for similar reasons, and it will only maintain the temperature inside - it will not bring the temperature down! It is on all the time and NOT controlled by the thermostat. All in all I think you need the 240v element replacing cost of element should be £15-20.
Hope this helps you.

bazzaboy
August 2009