I have an 2007 2.0d A6 Estate, couple of days ago I noticed that the A/C Heater blower (fan) would not come on. Tried the driver and passenger side dial to turn the fan on, and also the de-mister button, but the fan would not come on. Then whilst driving it came on, then would switch off. It appears to come on/off regardless of whether the dial is requesting fan speed.

More worryingly, the fan comes on when the ignition is off and the key removed. So yesterday it drained the battery, had to call out green flag. Disconnected the neutral terminal overnight, started ok this morning but the problem persists.

Does anyone have any idea what could be wrong?

Many thanks in advance.