well I wasn't consciously playing devil's advocate, but I was being trite
As you may know, the system uses motorised flaps, but there is no flap on the inlet to the blower. The principle of "climate control" is to mix to air-streams, one hot and one cold. The former comes from the heater-matrix (which is either fully-on or full-off) and the latter comes from the evaporator. The entrance to both streams is from the blower. The flap moves up and down according to the difference between the target-temperature and the measured temperature.