Just to add to the fun, my car is a +8, and a few years younger, but hey, it's still a Mog and I think of similar non-heatability. My original hand-book would confirm John's advice above, but it's exactly wrong for my car. Some years ago while at the factory I mentioned this anomaly and they very kindly supplied me with ... another hand book. Exactly the same in every detail except instructions for using heater, now Out for On (Oh, Oh!)
So in the end, like a previous Duke of York, I leave it half way in and half way out - but then I do live in Scotland.
