Same issue with my drivers side one, noticed mine was stuck on cold just after the summer. Took it apart using the method on rangerovers.net to drill a hole in the dash to get access to the ducting screw, worked a treat. Cutting the ducting out after that bit took two hours.
Glad I did it though because the matrix went after that, further surgery to the dash frame to get that out.
I moved the blend motor to hot for the winter, now it too hot so it needs sorting.
I am hoping the motor is ok, because you can buy potentimeters for them, and overhaul them I am told. I am going to have a go with mine, I have sent too much lately on it to not.