I had a similar problem with my 1.8 8v.
But my problem had to do with lack of power in the ventilation system, my blower worked properly, but there seemed to be a blockage in the vents. So there wasn't enough ventilation power to demist, aircon etc....
My evaporator was in desperate need of changing, apparently a common problem with 155's, 145/146's etc.....
I had to take it to a local specialist for changing as you need to remove certain lower parts of the dashboard.
All working properly now !
I hope it was of some help.