Coolant Temp warning lamp!

I bought a Fiat ulysse 6 months ago in Bristol. Complete with 12 months Warranty. During hot weather my wife has twice noticed the Aircon starts to get warm, followed a few minutes later by the "Coolant Temp" warning indicator lamp appearing (which in turn makes the stop lamp flash). The engine temp is only 80C when this lamp comes on, which is nowhere near an overtemp situation. I have also had an AC expert over to check the system and he said the AC is all working as if it were new. I contacted the RAC who underwrite the warranty and they tell me to take it to a garage for investigation. The RAC will not pay for the investigation, but will pay for the fault to be repaired (if it is a fault, not just regassing of the AC unit) They won't let me take it to a Fiat Dealer as they are too expensive (they only pay a max of £34 AN HOUR ON LABOUR). To cut a long story short, I can't get the fault to occur for anyone to be able to fix it. It is not an AC fault. Any Ideas.

PS I can't get a Haynes manual with wiring diagram cos they don't do one for the Ulysse! It's the 1.9D on a T plate.....

i have the exact same problem but i have a stilo 1,6....

the thing is that i cann't make it appear so when i speak to the dealer he stears at me as if i am an alien..

HEEEEELPPPP plz