Help please - Climatronic cutting out

Hi,

I've got a problem with the dual zone Climatronic on my 2007 vRS where it seems to die after about 20-30 minutes. It works perfectly normally at first, temps are OK and good airflow, then after about 20-30 minutes of driving the airflow from the vents drops right off (it's just passive airflow really). The display stays on, but adjusting the fan speed makes no difference, unless I turn it up to full in which case the airflow steps up slowly over about 15 seconds to normal power, everything works OK before it all dies again 20 minutes later! It can also be 'reset' by switching the Climatronic to OFF then back on again.

I've replaced the blower fan/resistor pack last week which has made no difference (with a £70 scrap part). VAG-COM shows no error codes at all for HVAC.

Does anyone have any ideas what might be causing the fault? When I spoke to the dealer about it they had never come across a similar fault.

Any help very gratefully received!

Greg