Defroster (windscreen demister)

["Gregory J. Edge" <edgr@mbari.org>]

1980 TR7 FI DHC

Anyone had the following and know how to fix?

Air flow control operates the lower flappers (floor registers) and main
vents when in the down position .

In the up position the lower flappers are closed , but still have flow
to the main vents and none directed through the defroster vents.

Nary a crack nor split in the dash panel so don't want to disturb things
that don't need to be in order to track this down.

Thanks.

GJE