my caravan fridge will not freeze or cool?

the gas flame stays on - I have had the burner section off and cleaned - checked the jet - and all is ok, the flame looks good and blue - I have tried standing the fridge upside down for 2r hrs - rolled it - reconected and tried again - but still no joy - is it possible the the internal coolant could be degraded - its 15 yrs old. It does cool down when I tried it on 240v - tho not very good - It is an electrolux wheel-arch type - and in very tidy condition, but wht wont it freeze? cany anybody help? please - Tom