Question about dash air vents

[Charles B Schiele]

First post! Hi guys. Been getting my Google questions answered here, so figured I'd start sharing some of my own. Got a '77 K10 over a year ago, and starting to get serious about fixing her up.

Start with a question: On the four air vents in the interior, are they all supposed to be functional on all models? NOT an A/C car. My "Center left" vent has been missing and appears to have duct-tape behind it closing the back hole. I want to get air flowing where it needs to be. Figured I'd make sure they all are usually functional before I start looking into the duct work, etc. The front-vents are super weak even when the fan is running - but the defrost vents work well, as do the heat vents. I've been super confused looking online since I am seeing some models without ANY apparent vents at all - I had no idea these trucks came without the outside vents. Is there even a fan in those models? And how does the A/C air flow in differently in those models?

Any good diagrams out there of how the vents route behind the scenes? Would also like, in general, a slide linkage reference if there's one out there. I want to know what baffles they are sliding so I can inspect them when I take the dash apart.

Also, my four-position fan switch only operates on FULL, that I have to troubleshoot. Is there a common hillbilly hack that often causes this? hacked wiring? bad switch? or should I just suck it up and bust out the multimeter when I have the dash apart?

Thanks in advance for any insight!

 

[1985c20]

If it’s a non ac cab/heater setup then the only place air should come out is the defroster or the floor. There were not originally vents in the dash around the cluster or the passenger side dash pad unless it was an ac truck. Yours must have been swapped in at some point.

 

[Charles B Schiele]

Aha! No wonder I was confused. Ok that will help me suss out my inner bits. I'll look for the signs of A/C delete.

 

[1985c20]

Does your hvac control have ac controls in it? If it does it sounds like you have an ac truck. Ac trucks all the air diversion was done through a vacuum system. Even the outside vents in the kick panels were opened and closed by vacuum pods depending on what setting you have it on. I’ve seen a diagram that gives you how the system is supposed to operate but I don’t have it saved

 

[Charles B Schiele]

A/C controls look like this? Sorry for glare - Cool---Hot bottom selector. Off--Heater--Def\_/ top selector. Four position fan (only top most ON works currently)

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[1985c20]

So that’s a non ac control then. Someone probably swapped your gauge cluster surround and dash pad to an ac one because it was in better shape at some point. Same reason my dash pad had the passenger vents in it haha

 

[Charles B Schiele]

Ah... but so it has all the vents too - that seems like a lot of work to add vents that don't do anything. So, NON AC controls, but all the vents? All this explains why I have been corn-fused. So are those vents useless?

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[dvdswan]

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So in this last picture. You look where your pine tree scent is hanging from. Non-A/C vehicles use this as fresh air intake to the cab. There is another on the driver side as well. PO must have changed the dash pad and instrument bezel from an A/C vehicle.

And yes, the 4 vents on the dash are useless.

 

[Mobius]

Your fan only working on high is because your blower resistor has gone bad. Replace the blower resistor and you should be good to go.

 

[Charles B Schiele]

Thank you! I hadn't dug into that yet, and perfect timing! Just got the engine humming sweet, it's getting into fall, so time to get the fan working properly! I'll check out the resistor!

 

[75gmck25]

The lower speeds on the fan go through the fan switch and it switches between the blower resistors (mounted under the hood). The high speed fan uses the blower relay (also under the hood) to provide direct 12 volt power to the fan, bypassing the resistors. The power wire for the high speed relay runs across the top of the firewall, and should have a 30 amp inline fuse.

Bruce