I've got a problem that after driving for about an hour, all ventilation into the car shuts down. All controls work fine before that. The fan can be heard when on full but a slight whistling as the air tries to get out somewhere. I'vtried with the pollen filter in, out and upside down if it was put in the wrong way last service. If the car is left off for about half an hour all seems to be back to normal - unless going on a journey for an hour our more. Could it be the HVAC resistor failing? I was thinking it is overheating/breaking down over timeshutting the stepper motors down. Ta, Terry.

I think the resistor pack, or FSR just controls the fan speed, so won't affect the vents opening etc.

Stepper motors are used on the vents I believe, controlled by the hvac.

I wonder if you have a faulty sensor somewhere. Can you get the faults read ? 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

Fan speed works fine even when vents seem to be closed. It just seems strange that everything works as it should, then the airflow itself seems to get blocked off after an hour or so's driving. I dont have access to a fault reader (one day!) and don't really want to go to the main stealer!

Are you sure the ventilation isn't doing what its supposed to?
After the initial heating or cooling the temperature eventually stabilizes such that the airflow into the cabin needed to to maintain conditions can be reduced significantly to the extent the airflow at any vent is imperceptible. Mine does very similar but the temperature stays constant and even in freezing outside air temperatures the windows stay clear.
For ac to work you don't need air blowing about all the time particularly when heating.
Does the temperature in your car settle at the dial setting?
Also do the windows mist at all? Usually misting is the first indication the ventilation is inadequate.

I first noticed it last summer whilst travelling through Germany and it getting bloody warm inside the car! The only way to let any air in was to crack open a window and tilt the sun roof! As a foot note this was the same trip when the gearbox packed up in Switzerland! That aside, using the vent/temp controls don't seem to make any difference, it will still cut off outside and recirc air after about an hour.

In that case it appears you have a problem.
Mine definitely copes with hot, sunny weather without any bother.
There are so many potential variables that could have a fault I think the only way to is to get a diagnostic check done and see if any faults have been logged. It's always possible that any fault could be cleared and never repeat.