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 ?

My guess is that it keeps "stuff" out of the blades.

Or maybe to keep the engine fan from pulling hot air out of the heat exchangers into the engine bay

Outlets, plural? Are you using an early fan?

Original '73 fan with single outlet mounted in original location. but installed a dual outlet adapter from a later model (I believe) To hopefully increase the heat.



This could be the answer.

I did mount the housing so the flapper would be closed by gravity when the blower is not running.

Your car should have a single outlet fan with a splitter for the hoses if you want heat to both sides. The cooling fan pressure should close the little door as engine speed increases. I don't bother with a aux fan. I just cap the jtubes with a couple of 2"(?) rubber pipe caps from the hardware store.

I hear that that is what the flappers on the engine fan do. But if gravity is holding down this flapper, I suppose HE air could make it's way to the engine bay if the flapper was not there.

Probably more of a chance that would happen than my "stuff" idea. Cause where is the "stuff" going to go if it is sitting on top of the flapper.

Click to view attachment

Factory diagrams show the fan outlet pointing damn near straight up. Well, more vertical than horizontal anyway.

That's the way I have it mounted now. It will only rotate to vertical so far then the fan housing contacts the relay plate.

Interesting picture. what do you think the white block is wire-tied on the side of the motor?
Maybe a block of felt or something to cut down on noise?
I have not seen this in any of the "originality" pictures.

Click to view attachment

Here's all I see in the manuals:
AND
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.

When the heating fan is not on, the engine cooling fan provides air to the heat exchangers to 1) heat the cabin or 2) to cool the exhaust pipes when heat to the cabin is shut off by the HE flappers.

The flapper valve in the heating fan keeps the air pressure from the engine cooling fan from blowing back through the heating fan thus maintaining pressure and airflow through the HEs at all times.