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02-26-2025, 11:57 PM
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#1 |
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Registered User
Join Date: Dec 2012
Location: Temple City
Posts: 3,659
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Heater/Ac ducting control
After a couple of years of just ignoring the poor wiring, and heater issues of my truck. I have decided to fix it so I can sell it to fund the purchase a Suburban or a wagon. My son, and I need a vehicle with more interior room for our winter trips.
So while the heater now works alot better, and shuts off fully. I can not switch the places the air comes out of. If i move the lever. It mostly still comes out the bottom. Where is a good place to start to look for the issue? |
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02-27-2025, 08:23 AM
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#2 |
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Registered User
Join Date: Oct 2013
Location: Alabama
Posts: 1,249
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Re: Heater/Ac ducting control
check the vacuum lines. my bet is one or more is either missing or broken
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02-27-2025, 09:43 AM
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#3 |
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Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,655
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Re: Heater/Ac ducting control
Does it still have the round ball on the firewall and vacuum line to the engine manifold?
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02-27-2025, 11:20 PM
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#4 |
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Registered User
Join Date: Jun 2011
Location: Central OR
Posts: 756
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Re: Heater/Ac ducting control
I dont remember what year your truck is.
Here is what I have saved for mine.
__________________
1955 GMC 250 8 Flatbed 1971 C30 157" 350 4spd 10' Flatbed 81 GMC K30 CnC 9' Flatbed 454 T400 89 GMC Jimmy Stock https://67-72chevytrucks.com/vboard/...d.php?t=810958 71 LT1 Convertible, 72 Coupe 69 CJ5, 75 CJ6, 67 M715, 72 M35A2 Bobbed, 95 XLC2 |
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Yesterday, 04:20 PM
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#5 | |
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Registered User
Join Date: Dec 2012
Location: Temple City
Posts: 3,659
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Re: Heater/Ac ducting control
Quote:
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Yesterday, 04:21 PM
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#6 | |
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Registered User
Join Date: Dec 2012
Location: Temple City
Posts: 3,659
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Re: Heater/Ac ducting control
Quote:
It was missing a couple lines, and I don't have the T on mine. What sub gen is that diagram from? |
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Yesterday, 04:23 PM
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#7 | |
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Registered User
Join Date: Dec 2012
Location: Temple City
Posts: 3,659
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Re: Heater/Ac ducting control
Quote:
I will have my son help me this weekend. |
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Yesterday, 05:12 PM
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#8 |
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Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,655
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Re: Heater/Ac ducting control
Hissing could be from a bad diaphragm in one of the the vacuum pots that move the flappers. Or a missing/broken hose.
On my 75: The Side Shroud should open when the control is set to MAX AC. It is over by the passenger kick panel. There is one near the throttle pedal that operates the Defrost/heat flapper. The third one is buried behind the dash and operates the bi-level flapper. There may be one for Vent. The flapper for Heat/Cold is a manual cable I think most of the squares are similar. |
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Yesterday, 10:30 PM
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#9 |
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Registered User
Join Date: Jun 2011
Location: Central OR
Posts: 756
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Re: Heater/Ac ducting control
__________________
1955 GMC 250 8 Flatbed 1971 C30 157" 350 4spd 10' Flatbed 81 GMC K30 CnC 9' Flatbed 454 T400 89 GMC Jimmy Stock https://67-72chevytrucks.com/vboard/...d.php?t=810958 71 LT1 Convertible, 72 Coupe 69 CJ5, 75 CJ6, 67 M715, 72 M35A2 Bobbed, 95 XLC2 |
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