Home » Public Forums » GMCnet » [GMCnet] plastic plenum on the pass side firewall
| [GMCnet] plastic plenum on the pass side firewall [message #112913] |
Mon, 24 January 2011 10:44  |
Gary Worobec
Messages: 867
Registered: May 2005
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Hi,
On the passenger side firewall right above the batteries is a black plastic plenum with a vaccum assist cannister on it that is pop riveted to the aluminum firewall. If I cut into this with 2 1/2" heater duct will this feed the cabin heat or is this for the windshield defrost.? I took out the OEM heater a while back and now want to add an auxiliary heater back in.
Thanks
Gary and Joanne Worobec
1973 GMC Glacier
Anza, CA
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #112933 is a reply to message #112913] |
Mon, 24 January 2011 13:47  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Gary,
Use this photo of the bottom of the plastic dash for reference:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=23846&title=view-of-the-plastic-da&cat=4899
http://goo.gl/VCh92
All heated and cooled air for dash outlets (NOT the lower center outlet for
cooled air) flows up through the horizontal top of the firewall into the
large rectangular opening in the black plastic. Hardly distinguishable in
that compartment is a deflector door which can direct air into the small
forward plenum defined by the left-right row of rivets -- that's defroster
air.
As pictured, the door is in the heat/cool position where all air flows into
the aft plenum to feed the dash outlets (fed by the two downward extending
ducts). At the very far end of the big plenum, just above the passenger's
downward extending duct, there's a small rectangular opening. That opening
matches with another hole in the horizontal top of the firewall and feeds
air into the plenum you asked about on the passenger side -- leading to the
rectangular foot heat opening at the passenger's feet. Not visible in the
photo are a similar duct and foot heat opening for the driver.
The various vacuum diaphragms and attached doors control where heated or
cooled air is routed, but in answer to your question, the vertical duct on
the passenger firewall DOES contain heated air for the cabin -- what there
is of it and for what it's worth.
HTH,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Mon, Jan 24, 2011 at 11:44 AM, Gary Worobec wrote:
> Hi,
> On the passenger side firewall right above the batteries is a black plastic
> plenum with a vaccum assist cannister on it that is pop riveted to the
> aluminum firewall. If I cut into this with 2 1/2" heater duct will this feed
> the cabin heat or is this for the windshield defrost.? I took out the OEM
> heater a while back and now want to add an auxiliary heater back in.
>
>
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GMCnet mailing list
List Information and Subscription Options:
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #112943 is a reply to message #112933] |
Mon, 24 January 2011 14:33 |
Gary Worobec
Messages: 867
Registered: May 2005
Karma: -1
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Senior Member |
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Thanks Ken, I think I got it now.
Thanks
Gary and Joanne Worobec
1973 GMC Glacier
Anza, CA
----- Original Message -----
From: "Ken Henderson" <hend4800@bellsouth.net>
To: <gmclist@temp.gmcnet.org>
Sent: Monday, January 24, 2011 11:47 AM
Subject: Re: [GMCnet] plastic plenum on the pass side firewall
> Gary,
>
> Use this photo of the bottom of the plastic dash for reference:
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=23846&title=view-of-the-plastic-da&cat=4899
>
> http://goo.gl/VCh92
>
> All heated and cooled air for dash outlets (NOT the lower center outlet
> for
> cooled air) flows up through the horizontal top of the firewall into the
> large rectangular opening in the black plastic. Hardly distinguishable in
> that compartment is a deflector door which can direct air into the small
> forward plenum defined by the left-right row of rivets -- that's defroster
> air.
>
> As pictured, the door is in the heat/cool position where all air flows
> into
> the aft plenum to feed the dash outlets (fed by the two downward extending
> ducts). At the very far end of the big plenum, just above the passenger's
> downward extending duct, there's a small rectangular opening. That
> opening
> matches with another hole in the horizontal top of the firewall and feeds
> air into the plenum you asked about on the passenger side -- leading to
> the
> rectangular foot heat opening at the passenger's feet. Not visible in the
> photo are a similar duct and foot heat opening for the driver.
>
> The various vacuum diaphragms and attached doors control where heated or
> cooled air is routed, but in answer to your question, the vertical duct on
> the passenger firewall DOES contain heated air for the cabin -- what there
> is of it and for what it's worth.
>
> HTH,
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> www.gmcwipersetc.com
>
>
>
> On Mon, Jan 24, 2011 at 11:44 AM, Gary Worobec wrote:
>
>> Hi,
>> On the passenger side firewall right above the batteries is a black
>> plastic
>> plenum with a vaccum assist cannister on it that is pop riveted to the
>> aluminum firewall. If I cut into this with 2 1/2" heater duct will this
>> feed
>> the cabin heat or is this for the windshield defrost.? I took out the OEM
>> heater a while back and now want to add an auxiliary heater back in.
>>
>>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #113029 is a reply to message #112913] |
Tue, 25 January 2011 05:59 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
Karma: 0
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I'm digging right now,,,,but just can't seem to dig fast enough. The boss just dreamed up ANOTHER project that she said she wouldn't need my help on. Remodle the 3rd bedroom into a sewing/quilting room. I was going to use it as my model airplane room with the grandsons. Havn't worked on the lazyboy dash for 2 weeks,,,,,,PL
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #113032 is a reply to message #113029] |
Tue, 25 January 2011 06:32 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Dig faster boy! They're catchin' up on ya!
Ken H.
On Tue, Jan 25, 2011 at 6:59 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> I'm digging right now,,,,but just can't seem to dig fast enough. The boss
> just dreamed up ANOTHER project that she said she wouldn't need my help on.
> Remodle the 3rd bedroom into a sewing/quilting room. I was going to use it
> as my model airplane room with the grandsons. Havn't worked on the lazyboy
> dash for 2 weeks,,,,,,PL
>
>
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http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #113090 is a reply to message #112913] |
Tue, 25 January 2011 14:05 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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Senior Member |
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Thanks for the information and photos of the underside of the dash - it explains many things. Now I can understand why airflow is so marginal in the coach - I don't think you could have added any more turns into the airflow path if you tried!
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: [GMCnet] plastic plenum on the pass side firewall [message #113271 is a reply to message #112933] |
Thu, 27 January 2011 09:01 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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Senior Member |
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You know
looking at the plastic duct and air entrances/outlets, it looks like a workable system. I wonder where it actually fails???
A door failure I can understand but I don't think that is the cause...
Long controversy I guess....
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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