Same problem on my old 2006 1.3 Multijet. Turns out Fiat know of this problem which is the connector for the fan/heater in the passengers footwell, at the top. The loom isn't long enough and the connectors pulls out all the time. On my mum's Grande the orange cable overheated and turned brown. Fiat won't admit there's a problem but there's an "enhancement" to get it sorted at the cost of £150+. They won't call it a modification as that is an admission of blame on their part.