Hi to all.Car's (TD6)heating has the following problem.
For having hot air in car i must ONLY follow specific procedure:
1.To set both temp knobs to max temp position ( so i can have only really hot)
2.switch on heating only when car is on very low speed.
When on higher speeds if i reduce temp even by one degree from max either fm driver's or co driver's knob,then air from respective side and also from back seats vents, gratually becomes cold and if i want to make it warm/hot once again i must reset knob to max temp and really reduce speed or stop moving car.

Any idea what can cause such a problem,other than stepper motors which checked by the workshop and found ok
can it be hvac programming as per workshop suggestion?????

many thanks for your assistance.

It does sound like something is wrong with the flaps being operated and that it is mechanical. I suggest that you do the hard work and take the dashboard apart and first see if it is dirt etc. stopping the operation and secondly find out which stepper motor is acting up. Big job to do from what I remember  MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!

Ebajema thanks for your reply.According to workshop when they plugged car in computer flaps normally opened/closed so always as per them problem is not from there?????