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[GMCnet] 78 dash heat/A/C. How does it get outside air? [message #332884]

Thu, 31 May 2018 20:51

BobDunahugh

Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA

Karma: 11

Senior Member

Trying to figure out where outside air gets into the heat A/C box. Openings at the back of the box go into the coach. The opening on top of the box go to the defrosters. There are no openings in the left, right, bottom, or front. Remember that this box is used only on 77, and 78 GMC's. Have photos if interested. Bob Dunahugh 78 Royale
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Re: [GMCnet] 78 dash heat/A/C. How does it get outside air? [message #332885 is a reply to message #332884]

Thu, 31 May 2018 20:59

Emery Stora

Messages: 959
Registered: January 2011

Karma: 4

Senior Member

Bob
Only part of the air is from the outside. There is an opening in the top passenger side of the box. That brings outside air in. Not just to the defrosters. It leads into the area where the fan blower is. The rest of the air for the heater is recycled from the inside. There is an opening at the floor by the passenger feet.

I blocked off the outside air opening and then I blocked open the door inside the opening by the passenger’s feet so that I have 100% inside air recirculating. There are enough air leaks in a GMC so you don’t have to worry about outside air.

Emery Stora
77 Kingsley
Frederick, CO

> On May 31, 2018, at 7:51 PM, Bob Dunahugh wrote:
>
> Trying to figure out where outside air gets into the heat A/C box. Openings at the back of the box go into the coach. The opening on top of the box go to the defrosters. There are no openings in the left, right, bottom, or front. Remember that this box is used only on 77, and 78 GMC's. Have photos if interested. Bob Dunahugh 78 Royale
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Re: [GMCnet] 78 dash heat/A/C. How does it get outside air? [message #332886 is a reply to message #332884]

Thu, 31 May 2018 23:49

BobDunahugh

Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA

Karma: 11

Senior Member

Bob Burkitt sent my some photos. Thanks SO MUCH Bob. There is a vacuum controller door that is out of site above the blower motor. On top. I had felt the door. But thought it was the top of the heater box. The door is stuck in the position that blocks off the outside air from coming in. ( But far from 100%. ) Bob had put a wire mesh over that opening to keep critters out. Great idea. Nice job. I'm going to make a plastic cover over that opening in the morning. I want to keep any hot air from entering the cold air area of my A/C system. Should also help in cold weather with the cold air infiltration. Yes. I'm blocking fresh air from entering the system. These GMC's just aren't that air tight. If I want fresh air. I'll adjust my Wind Wings. I've got a heater, and A/C system that I want to get every bit of performance out of them both I can. Thanks again Bob. Bob Dunahugh 78 Royale.

________________________________
From: Bob Dunahugh
Sent: Thursday, May 31, 2018 8:51 PM
To: gmclist@list.gmcnet.org
Subject: 78 dash heat/A/C. How does it get outside air?

Trying to figure out where outside air gets into the heat A/C box. Openings at the back of the box go into the coach. The opening on top of the box go to the defrosters. There are no openings in the left, right, bottom, or front. Remember that this box is used only on 77, and 78 GMC's. Have photos if interested. Bob Dunahugh 78 Royale
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Re: [GMCnet] 78 dash heat/A/C. How does it get outside air? [message #332887 is a reply to message #332886]

Fri, 01 June 2018 00:24

Bill Van Vlack

Messages: 419
Registered: September 2015
Location: Guemes Island, Washington

Karma: 14

Senior Member

That's the Recirc door. If you make the damper work you can have choose between Recirc or fresh air. Helps on those days when there's plenty of cooling from outside air and you don't want to listen to the wind wings.

Bill Van Vlack '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.

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Re: [GMCnet] 78 dash heat/A/C. How does it get outside air? [message #332889 is a reply to message #332884]

Fri, 01 June 2018 07:09

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

Feeds directly to blower wheel under pass windshield. Recirc door opens near pass left foot area under dash.

John Lebetski
Woodstock, IL
77 Eleganza II

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