Thanks for the suggestion.The coolant temp sensor does appear to be working. It has an impedance and when i touch a 4.5v battery across the terminals the engine note rises but the fan does not come on. (also reversed polarity and the engine note dropped.)

So my thinking is.

The circuit to power ...

Thanks for the diagrams. Really helpful. I think the issue is the emu not sending a switch on signal to the relay. Since the AC does have gas pressure and the temp gauge is registering. I think the issue may be the emu itself.

Sorry to re-open this thread.I would welcome some advice on how to track down a problem with my Y plate 2L petrol bongo with digital AC.

Driving in traffic last weekend (Mid March and chilly) and noticed the temp gauge climbing. Usually it stays firmly resting on the left hand end stop unless ...