Weird AC problem

[east302]

Does the air flow, other than the "dash" setting, match what is selected on the a/c control?

Check the mode actuator by the gas pedal. See if the linkages are intact. There is a notched dial on the actuator that will rotate as the damper is positioned. See if it turns in response to selecting defrost-panel-floor on the control.


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[Echomirage]

the air door actuator is brand new. thats one of the things i thought was wrong the first time, so it was replaced. the air flow matches everything else: floor, defrost, floor/defrost blend. just nothing out the dash vents.

 

[east302]

Here are the positions on a 98, note the changes in dial notch and linkage position. See if yours matches:

Dash:

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Floor:

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Defrost:

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The actuator responds based on varying voltage signal from the control panel. It may be that the damper door is dislodged or hanging up in the box (so watch how the linkages change) or the controller may be the issue.

Turn ignition on, remove the connector at the actuator and connect a multimeter at the white wire cavity and a ground. Adjust the air position dial between panel-floor-defrost and see how the voltage changes. It should be smooth, not erratic.

You should see around 12V on dash, 6V on floor and very low (1V or less) on defrost.

If it jumps around or you have no voltage at a certain position, I would suspect an issue in the controller.

When you reconnect it, make sure the air position dial is in the same place that it was when you disconnected it.

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[Echomirage]

the depth of knowledge some people have about cars amazes me. when i was making a 3rd gen camaro into a race car, i had a guy tell me on the phone the exact color of each wire in a section of the main harness, and what each wire did.

i dont know if ill mess with this, or give it to the shadetree mechanic and let him dive into it, since he promised to get the AC finally working. but i appreciate the detailed help im getting here.

so the hvac controls are all electric, no vacuum on it at all?

 

[east302]

The only vacuum would be on the Tahoe/Suburban that used a heater control valve. Air duct controls are electric.


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[Echomirage]

I'm finally messing with this. I watched the new motor while changing the vent. It turned properly. I then swapped out the old motor, and it also turn properly. Is the issue with the blend door itself getting hung up? My guy said he changed that already, while trying to diagnose this issue.

 

[east302]

So when it is on the dash setting, the notches on the dial are at approximately 1 and 7 o'clock? The linkages move as well and the floor/defrost air flows are correct? Do the linkages match the ones in the photos a few posts up?

If so, I'd guess that it's something with the door in the air box. Maybe some foam insulation has shifted and is blocking something, I don't know. I'm 99% sure that you have to pull the dash to really get in there and see what is happening. You sure your guy did that?

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I think the bottom of the box can be removed and give you limited access to the air door. Maybe take a mirror and see if you can spot anything.

Also check the ends of the linkages where they connect to the air box. See if the air door shaft has come off or gotten pushed in somehow. I've heard where that can happen and can be (somehow) pulled back into position. Maybe add some type of metal clip to the end if it is trying to slide back into the box.


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[east302]

Here's a link with better photos of the linkage pieces...

http://www.gmt400.com/threads/no-air-on-driver-vent-only.30762/


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[Echomirage]

the notches line up properly, and the linkage is free and unobstructed. i dont know exactly what my guy did, but i know he sure as hell didnt gut the dash like in that pic. he said he ordered a 'blend door' from the dealer, and installed that. he may be flaky in some things, but his work is excellent. he wouldnt lie to me about that, and hes worked on the truck several times and didnt charge anything, since this AC is an ongoing problem.

he swapped the motor, got everything hooked back up, then fixed an alignment issue with the belt when pulleys didnt line up, because this was originally a boat motor. he paid for a new belt himself, and found proper washers to bring everything into alignment.

all that being said, next time i talk to him, ill ask exactly what he replaced, because this didnt happen until after he changed that door. i still havent even fixed the core freezing issue. i did get that switch, but as its ever so slowly getting cooler, AC isnt needed as much now.

 

[Mrozu]

You should see around 12V on dash, 6V on floor and very low (1V or less) on defrost.

hello,

I know I'll receive golden shovel, but I have a problem with my '96 Tahoe. On this white I have 7,6V dash, 7,3V floor and 6,3V defrost. Where should I go next? What to check, fix or replace?