AC/Heater Help

[BlazerDave87]

I know there has been a lot of posts about AC/Heater controls, etc.

I have an 82 K5, mostly original (except engine is a crate 350).

My question is that regardless of where the heat selector is placed, hot air is ALWAYS coming out of the heater vent down below as well as the vents. The upper selector does redirect the air for the most part to the location you choose, but there is always hot air coming out. It's much hotter if you move it over to HOT, but believe me when I say there is nothing COOL about the air when it's moved to Cool. I don't have the AC hooked up right now because it would need to be recharged, but this issue seems more to do with something else. I love driving it, but I'm relegated to morning and late evenings during the summer here in Northern CA.

Any help would be appreciated

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[Frankenchevy]

Did you check the cables on the back of the hvac controls?

 

[BlazerDave87]

Yes, I have. I made sure that the throw on the cable when it actuates the lever behind the glovebox takes it from one extreme to the other

 

[Snoots]

You could have a relaxed control vacuum diaphram. Check all of your vacuum lines. Especially the feed from the engine. I believe it's right behind the carb.

 

[BlazerDave87]

Thanks. I'll check that out.

 

[75gmck25]

If you remove the glove compartment door (five screws?) you will see a vertical panel on the heater box, with a couple of screws holding it. If you remove that panel you can see the heater blend door, which is what shuts off the heat flow. On top of the heater box you can see where the heat cable attaches, and where you can adjust it to make sure the door has full travel.

If your truck is typical, something has fallen down in the defrost vent and is preventing the heat blend door from shutting off the hot air flow. Its also possible that the rubber seal on the blend door is shot and not making a good seal. The heater core is full water flow and always making the box hot, so you will never get completely cool air, but at least make sure this door is shut and closing off the air flow through the heater core.

Bruce

 

[1985c20]

You could add a shut off valve/bypass loop in the heater core feed pipe. That way there was no hot water flowing through the heater core.

 

[MikeB]

My 82 C10 without factory air has a similar problem. I have totally gone through the heater box and have the air doors sealing as well as possible, which isn't all that great. I think the main problem is hot coolant is ALWAYS flowing through the heater core, and even with a slight gap between air door and box, fresh air is warmed up 10-15 degrees. That's still cool air on a 30 degree day, but it's very hot air on a 90 degree day.

I like the bypass valve idea, but need to find one that works with 5/8" and 3/4" hoses.

Or I could use a simple shutoff valve on the heater core inlet hose. But with my Vortec heads, the heater core acts as a t-stat bypass. Guess I could always use a Stewart t-stat with bypass holes. Actually have one in sitting on my workbench. Maybe that's a project for today. Nothing is as fun as pumping out coolant!

 

[BlazerDave87]

Those are great ideas everyone. I guess I'll be tearing into that this weekend!

 

[MikeB]

I found vacuum and cable actuated bypass valves that work with 5/8 and 3/4 hose.

https://shop.advanceautoparts.com/p/carquest-vacuum-bypass-closes-heater-valve-74781/15490012-p

https://www.amazon.com/Cable-Operat...&pd_rd_r=64086fe0-2ad2-4b91-9faf-c6940fff0344

Also, one that uses a servo motor.
https://www.amazon.com/Electronic-B...&pd_rd_r=64086fe0-2ad2-4b91-9faf-c6940fff0344