You are right about that, Carl.
But, only someone who knows how the 53-55 Air Flow heaters works would understand why
based on that illustration in the 1954 Accessories brochure the source of the "air flow" can be adjusted.
It is, however, quite easy to understand how the 47-52 cable-control works - it simply provides varying amounts of defrost to the windshield and/or heat directed towards the floor. The outside, fresh air, is always going through the heater core.
