My aircon will not work when I first start the car, after 15mins of driving and turning the car off and on again it usually comes on althpough displays the little fault book. After an hour or so driving switching off and then on again it works even better and the computer does not display a fault book any more........?

Any Ideas?

its bollixed,,it sounds like it could be a faulty hevac unit.,what model of p38 is it.

Get a diagnostic check done on it. Maybe the gas level is borderline.