Flapper in heater fan, What does it do ? Options

[Olympic 914]

The heater fan motor was pretty cruddy so I disassembled it and polished the armature and greased the ends then bench tested it and it ran pretty good. loosened the bolts on the housing and while it was running wiggled it around a bit until it ran the smoothest. when I reassembled it I noticed a clear plastic flapper inside the blower housing. No spring on it to hold it closed. When I put the fan in the car with the outlets pointed in what looked to be the best direction, pointing towards the pass side, the flapper valve hung open.

Looked at the "originality photos" and see that the outlet was installed to point straight up (?) in this position the flapper closes by gravity and would open whenever the fan is blowing.

What does this flapper do ?

[McMark]

Here's all I see in the manuals:

A suppressor is attached to the blower motor in vehicles equipped with a radio.

AND

The suppressor, if installed, should be connected in the same way to both cable ends. The plastic cover must be pushed back over the suppressor in such a way that all connectors are covered. The suppressor should be reattached to the blower motor with a plastic hose clamp (at least 250mm long).

It's not uncommon on cars from this era to have noise suppression on most electrical motors and other EMI-noisy devices. So this suppressor was probably part of the original design, but didn't make it into any production cars.