The very first thing I would say is that I completely disagree with Lorne as to the reason why hot air continues to circulate when the heater knob is turned completely anti-clockwise.
I respect disagreement. So thank you for yours. But my fix is so common sense. Additionally, it has worked over and over and over again with later AC Morgans.
The AC instantly becomes what you would expect from a normal air conditioned car. We can argue about rationales but a
de facto solution is always to be respected.
It also stops the condensation that drips into the foot wells or wherever.
(the fact of water adhesion means that the dripping can be anywhere under the dash.) That same condensation, after it has begun, rusts the controls, which could be the cause of your hyper stiff vent control. Rust, grease and dirty does not help its movement.
..... I have little interest in the complexities....
That being said, I am with Luddite. Extraneous add-ons, unnecessary to power, aesthetics, comfort, braking or cooling are not of a keen interest to me. They make the cars harder to use and maintain. However, if I am asked to help a mogger achieve want he/she wants, I have be known to point out the obvious.
Why don't you take a 10 quid risk and try mine out?
gmg