Missing air vent component?

[texdave]

I have a 76 GMC Burb and am troubleshooting why I don't get a lot of air flow when I put my HVAC controls on Vent or AC. Blower motor was replaced last year and it works across all speeds. Last year I did have the passenger side kick panel replaced with one that allowed for a speaker.

I took off the dash panel and glove compartment to take a look at the ducts and vents. When I look behind the kick panel, I noticed that I can see directly into the blower motor itself. That doesn't feel right.

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Am I correct in thinking that it needs to be blocked off? If so, is it the #7 or the #4 pieces in this LMC page that I need to get?

 

[EvilGenius]

The part of the blower you can see is the intake. The hvac pulls in fresh air from that void in the cab. It's fed fresh air from the cowl. Being able to see it like that is normal.

My guess as to your flow problems is worn out seals. The blend doors and individual joints in the airflow path have seals on them that turn to dust over time. If you have never taken the interior hvac box out it would be worth it to replace all the seals for the best performance.

 

[legopnuematic]

Looks like you are missing the plenum valve/fresh air valve. You should have a flapper in the cowl, visible under the cowl screen outside, when you are in a non recirculating mode it allows fresh air from the cowl, and directs it to the blower, in recirculating mode (max ac for example) it will close the fresh air duct and open that flap to allow it to recirculate.

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Photo grabbed from the net for reference.

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[texdave]

Appreciate the responses everyone. @legopnuematic I took a look at my service manual and the "Plenum valve" actually refers to the valve/flapper on the cowl that controls the outside air flow. The part I'm missing is apparently the "Air inlet valve" which should open up when AC is on Max mode so it can recirculate air. You may be right actually on the naming. LMC refers to it as "Air Vent Bezel" and valve. I'll be sourcing that part again, it'll be interesting to see how I can get it in place while still retaining the kick panel with the speaker.

@EvilGenius thanks for the heads up about it being an intake. Indeed, i can feel the flow of air going into that section when I turn the system on. I am taking most of the ducting and all of the vents off and am planning on cleaning them up and replacing the seals where needed to minimize air loss.

While I was testing the main temperature mix door/lever on the main plenum, I saw that there was a lot of old insulation material stuck in the area where air comes in from the blower. Here's what I removed and I have to imagine that this was playing some part in the low air flow at the vents.

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