How can I fix my Dometic - Electrolux RM4230 Gas Fridge ?

Hi, I have this fridge fitted in a static caravan. It lights but the fridge does not go cold - in fact it seems to warm up!
Any ideas as to what is wrong and how I can fix it. Someone suggested I took the fridge out and inverted it and shook it a few times - did that and it made no difference.
Thanks.