Heat/AC Distribution Troubleshooting/Vacuum Control

[89Suburban]

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[McCSquare]

Maybe I'm missing it here... But my defrost setting doesn't work. Heat blows really hot into the cabin, but I don't get a thing from the vents up by the windshield. What should I look at? Defroster actuator? Where do I find it?

 

[Jims86]

Maybe I'm missing it here... But my defrost setting doesn't work. Heat blows really hot into the cabin, but I don't get a thing from the vents up by the windshield. What should I look at? Defroster actuator? Where do I find it?

Try putting it on heat, and see if anything comes from the defrost vents. I still have to take mine apart again because I switched the vac lines around.
Btw John...that Diagram is kick ass. Exactly what I needed.

 

[89Suburban]

If you have air conditioning the defrost door is right above the floor heat outlet, the vacuum servo is on the side facing the accelerator pedal.

If you do not have a/c a cable controls that door.

 

[McCSquare]

If you have air conditioning the defrost door is right above the floor heat outlet, the vacuum servo is on the side facing the accelerator pedal.

If you do not have a/c a cable controls that door.

It has/had air conditioning, it just doesn't work. I definitely have the controls. I'm guessing that the vacuum line for the defrost door isn't operating. I did a vacuum test on the carb and it had no leaks... Should I repeat the test but try turning on the defroster? Or do I use a special test point?

 

[89Suburban]

First thing I would do is make sure the vacuum line for the controls is even hooked to the engine to begin with. It comes out of the firewall on the passenger side through the same grommet as the heat/a-c wire harness:

Then check for vacuum at the floor/defrost servo:

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Here is an internal pic of the defrost/floor blend door:

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[chengny]

Thanks to the OP for these photos (Mr. 89Suburban) - hope he doesn't mind that I wrote graffiti all over them:

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[McCSquare]

Thanks to the OP for these photos (Mr. 89Suburban) - hope he doesn't mind that I wrote graffiti all over them:

Thanks to you guys for all the photos and info. Now I've gotta tear apart this dash and diagnose this thing.

 

[89Suburban]

You don't have to tear anything apart, the hose and servo is right there next to the go pedal.

 

[McCSquare]

I turned on the heat and put the ac to lever to defrost. There is a distinct hissing when I remove the vacuum line from the actuator/valve at the floor vents by the "go pedal". There is very little flow down at the feet either.... Do i have a broken actuator?

 

[89Suburban]

Is your fan working right? Do you have good air flow out of the a/c vents?

 

[McCSquare]

Yeah seems strong enough. She makes a great deal of racket, sometime it squeals a bit. But full blast heat will singe my beard. Feels like strong airflow... I wonder if I have bad seals somewhere?

 

[89Suburban]

Take that diffuser off like chengy said and see if that trap door is moving. Did you do that? I'm about all out of advice for you. We put a lot of diagnosing info here but you don't seem to be following it and reporting back, just asking the same thing.

Plug the vacuum hose back on and take that diffuser off and see if that trap door is moving or not with the controls.

By the way yes there is a seal against the firewall and if it is shot it will blow some air behind the housing but not enough to affect your other functions unless the whole housing itself is loose. Is you housing nice and tight to the firewall or can you shake it?

 

[McCSquare]

Take that diffuser off like chengy said and see if that trap door is moving. Did you do that? I'm about all out of advice for you. We put a lot of diagnosing info here but you don't seem to be following it and reporting back, just asking the same thing.

Plug the vacuum hose back on and take that diffuser off and see if that trap door is moving or not with the controls.

By the way yes there is a seal against the firewall and if it is shot it will blow some air behind the housing but not enough to affect your other functions unless the whole housing itself is loose. Is you housing nice and tight to the firewall or can you shake it?

Bumping from the dead...

I took off the diffuser on the floor, and the door does close on the floor when I move the lever to defrost. It does this slowly, and once or twice I had to wiggle the lines behind the control panel.

When the door was closed I still didn't feel any hot air coming from the defrost vents. I felt a bit of cold air on my hand... but I assume its just from the windshield...

I was looking at your other threads and it seems like there is some "blender" door or something that pulls air from the outside? Where do I find this? Could it be stuck open? I'd be surprised considering how damn hot the heat is otherwise.

Also I tried wiggling it and nothing seems really loose that I can see. I'm pretty stumped now.

 

[8T6K5]

Quick interuption, 89s do you have the rest of that manual scanned? I wouldnt mind seeing pg178, have Q about switch for rear air....