Well a brief update, I pulled apart the passenger foot well. The servo works when heating is adjusted between max cold and max hot. This is same on drivers side so these are both working and blending the air mix as they should. However I noticed the control flap that adjusts where the air goes to, foot well, windscreen etc was jammed shut. On the drivers side high up is the third servo and having disconnected the lever the flaps work so its the servo that's stuck in one position. Then I noticed the wiring has been unplugged. The loom is no where to be seen. I'm guessing the servo was knackered and previous owner disconnected it, jamming the flaps so there was always hot air going to the windscreen for winter defrosting. I have managed to remove the first screw holding the servo in but the one at the back is a pain. No space as the parking brake pedal is in the way. Lets see how I get on tomorrow.