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?

Re: Heater/Ac ducting control
 

check the vacuum lines. my bet is one or more is either missing or broken

Re: Heater/Ac ducting control
 

Does it still have the round ball on the firewall and vacuum line to the engine manifold?

Re: Heater/Ac ducting control
 

I dont remember what year your truck is.
Here is what I have saved for mine.

Re: Heater/Ac ducting control
 

Yes. It holds vacuum. I also t tested it by setting the engine to high idle with it removed, and it made no difference.

Re: Heater/Ac ducting control
 

Mine is a 83.

It was missing a couple lines, and I don't have the T on mine.

What sub gen is that diagram from?

Re: Heater/Ac ducting control
 

I hear hissing somewhere, but over my engine and exhaust. It's hard to pin point.

I will have my son help me this weekend.

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.

Re: Heater/Ac ducting control
 

https://www.73-87chevytrucks.com/tec...ice_Manual.pdf

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