This question just popped up on the TR7/8 mailing list and it was something I have to do as well.
The demister vents just below the windscreen have quite a lot of leaf debris trapped against the mesh and it reduces the air flow quite a bit. Does anyone have a way of clearing it without taking the whole dash out? One suggestion is to blow the rubbish back down into the main heater body with an air line where it might be possible to reach with vacuum cleaner nozzle. Or maybe try to break it up with something like a welding rod whilst sucking with a vacuum nozzle.
Russ
1981 TR7 Sprint DHC
Dursley
UK
http://tr7russ.blogspot.co.uk/