check fuse first, usually motor siezed, if you tilt cab you can access motor from underside ,you need to check for a live feed ,if ok try turning fan it should be free to turn.motor comes with plate fitted on it.spray fixing studs before removing nuts [they tend to snap off if tight.]
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix lorries/trucks.