AC duct difference

[b_hill_86]

Pictured is my duct and a spare I have. Mine is the clean one of course but I noticed mine had that rectangular hole in it and the other didn’t. I assumed someone cut it in but recently I saw another with the same hole which led me to believe some got it and others didn’t.  Any idea why? I was going to use the one without the hole thinking it would provide better airflow without an escape.

With its positioning I thought maybe it was to help cool the back of a console mounted 8 track player but that’s just a theory.

[wheels78ta]

Mine has that rectangle cut out also.  I have the AM FM 8 Track but it was one unit in the dash.

[b_hill_86]

Hmm.

[nUcLeArEnVoY]

Mine doesn't have the hole, and I don't have an 8-Track player, I just have the standard AM/FM radio. I do have CB radio, though.

I think your theory may hold some truth to it.

[aussieta]

is it to do with some cars had ac outlet under glovebox and steer column and some did not

[Wallington]

That's just ducting for AC cars vs non-AC.

Interesting, was having a look at a few diagrams and assembly notes but nothing specific mentioned. What I did remember was that non-console cars had their own floor vent setup cover from the heater box, which I don't recall seeing in the flesh. #3967971 I think, I closed the page, but unrelated.

[sreta]

To add more confusion, there is a third version of this duct, which I bought from ebay. No rectangular hole, with two mounting points. Now we have two versions of the next duct. Two holes vs one hole.

[b_hill_86]

Ben, I’m sorry I hadn’t seen your response here until now but what you said makes sense I suppose.

Sreta, that’s interesting. I never knew there were ones with different mounting holes. That would certainly pose an issue if someone bought the wrong one. 

[sreta]

Ben, are you talking about this part ?

[Wallington]

That's the one, #3967971.
Features in the 1976 Assembly Manual, deleted by the 1980 Assembly Manual. Generally column shift base-models with no console.

What's that photo of?

Firebird heater box diagram 1976 floor duct 3967971 by Ben, on Flickr

[sreta]

I don't know. I was looking for ductwork hardware and this picture showed up. It's from Firebird Central.

[Wallington]

https://www.firebirdcentral.com/1970_1981_Firebird_Under_Dash_Heater_Core_Case_p/htr-60d.htm

[TA301]

Same generation Camaro ducts are identical with minor differences such as the ones you see here.

[Wallington]

It was only a day or so ago that I stumbled across a pic that would have worked here. I think I was looking up console pics, I was not home. And one unrelated pic that came up was a Camaro with dash removed and all the round flex hose, but the post was for Firebirds. I think it was an ad and they just used the first pic that came up and was not even correct. But at the bottom was the same, or similar, floor vent for no console cars.