Heat/AC Blend Doors

[Charlie]

I have a 74 pdf manual. Looking for someone to confirm how many blend doors I have. The diagram shows 3. Defroster Door, Air Door, and Temperature Door. I know there is one at top of the passenger kick panel but I have never had one of these apart to know the exact number. I am thinking mine need to be replaced and don't know if it is a big job to do. Will also need to search to see if these are available to order somewhere.

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[Craig 85]

Here's a few pictures from my '85. Your's should be similar, but I know my vacuum hoses are color coded a little different that this chart. For reference, the piece in the back ground of the 1st photo with the yellow and red boxes is supposed to lay on top of the piece in the foreground.

There are technically 5 doors/flaps that open. Three are in this picture, the other 2 are for recirculating air. The one in the yellow box is controlled by a cable attached to the top of the box (Hot/Cold slider on head unit). The one in red box is controlled by the vacuum pod in the red box. That pod is the only one that pushes and pulls with vacuum hooked to both sides of it. The last door pictured here is positioned horizontal on the bottom left of the yellow box (also photo #3 & #49 in photo #2). It controls defrost. The vacuum pod will pull this door toward the rectangular opening at the bottom center of the photo to close off the floor vent and direct air towards the windshield.

In photo #2, the vacuum pod near #53 are depicting the same pod, just 90 degrees off so you can see the movement of the defrost door.

The other 2 doors not pictured are the one at the right kick panel and the flap under the cowl (near yellow arrow in photo #4) that blocks fresh air when the kick panel door is open to recirculate air from the cab on Max mode.

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[Charlie]

There could be some differences in the year models. The diagram in my OP was not what I intended to upload. Could not delete after discovering how bad it is.

 

[RoryH19]

Here's a few pictures from my '85. Your's should be similar, but I know my vacuum hoses are color coded a little different that this chart. For reference, the piece in the back ground of the 1st photo with the yellow and red boxes is supposed to lay on top of the piece in the foreground.

There are technically 5 doors/flaps that open. Three are in this picture, the other 2 are for recirculating air. The one in the yellow box is controlled by a cable attached to the top of the box (Hot/Cold slider on head unit). The one in red box is controlled by the vacuum pod in the red box. That pod is the only one that pushes and pulls with vacuum hooked to both sides of it. The last door pictured here is positioned horizontal on the bottom left of the yellow box (also photo #3 & #49 in photo #2). It controls defrost. The vacuum pod will pull this door toward the rectangular opening at the bottom center of the photo to close off the floor vent and direct air towards the windshield.

In photo #2, the vacuum pod near #53 are depicting the same pod, just 90 degrees off so you can see the movement of the defrost door.

The other 2 doors not pictured are the one at the right kick panel and the flap under the cowl (near yellow arrow in photo #4) that blocks fresh air when the kick panel door is open to recirculate air from the cab on Max mode.

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The one by the yellow is the most work to replace IMO. Have to remove the cowl and cowl screen. At least in the 81+. It's easier on the earlier ones since they don't have the metal cowl screen.

 

[75gmck25]

To start out I would remove the glove box (5 screws) and then then remove the vertical plenum piece behind it (2 screws?). Now you can see into the box and view the two main blend doors. They are connected with a metal bracket on top, so they more or less move together based on the heat selector and the flow selector controls.
- In many cases something has fallen down through the defroster vent and it’s blocking the door movement. Treasure hunt!
- The vacuum actuator pod is behind the door you see in front, and its rod connects to the door using a small plastic bracket and metal pin mounted to the door. This plastic bracket frequently breaks. This is one example of where you can get the bracket. https://www.americanclassic.com/197...VqmQfePWeoqF97uibISR-mXvNS3IvQEsaAsnsEALw_wcB

Bruce

 

[Charlie]

I have noticed when the selector is set to OFF, air is still coming into cab thru the vents. The amount differs due to vehicle speed. I have deleted the low speed fan and it does not blow all time on low setting so I know the blower motor is not running.

Is there a door that should close not allowing air inside cab when selector is set to OFF?

 

[Dave M]

l would go down the path as 75gmck25 stated in the above post. I 'm sure he is spot on the money. Had the same issues with mine. An easy fix.

 

[Octane]

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[75gmck25]

On an A/C truck there are 2 vacuum actuators to control air intake for the HVAC. One is easy to see on the passenger side kick panel once you remove the small plastic piece around it. The other is under the hood and under the plastic cowl filter /cover. Just pull the plastic filter off and you can see the vacuum actuator tucked up under the outside edge.

The actuator in the cowl is open to outside air all the time unless you put the A/C on max, and then it closes down to only 10% flow. At the same time it will fully open the kickpanel actuator so the flow will be mostly inside (recirculated) air.

Both of these actuators connect to the same vacuum port on the controls, using a T fitting that is up behind the glove box. It’s easy to see and troubleshoot once you remove the glove box.

Bruce

 

[Craig 85]

I have noticed when the selector is set to OFF, air is still coming into cab thru the vents. The amount differs due to vehicle speed. I have deleted the low speed fan and it does not blow all time on low setting so I know the blower motor is not running.

Is there a door that should close not allowing air inside cab when selector is set to OFF?

I believe the trucks are designed this way. I've had 8 of them over the years and they all will flow air a small amount of air even with everything shut off.

 

[gmbellew]

so, i was having a similar issue regarding air distribution. i took out the glovebox and vertical duct piece. i saw a clip broken and replaced it. i also saw the rod that connects the two doors was popped off the second door. i reattached it.

it appears that the second door swings closed in heat mode and open in vent/ac mode. the second door works great in heat mode and all air comes from the floor. the primary door kind of helps the door close.

but it doesn't want to swing open in vent/ac mode. the metal rod spins like it is supposed to when the primary door moves the metal rod, but the door doesn't move. it is like there should be more friction or something. i tried quickly shoving some rubber to add more friction, but it didn't work. if the door doesnt swing open, it prevents air from coming out of the vents like it should (low flow).

can i just use a dab of super glue to connect the rod to the door? is there a piece missing? should I rip out the second door?

pic of second door in open mode attached. it won't do this after cycling to heat and back to vent.

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pic of second door in closed mode (with first door still in ac mode. normally the main door would also be closed when this is closed.)

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[gmbellew]

got it figured out....i clipped the rod connecting the two doors back wrong. after some adjustments it works as well as 30yr old doors and seals are going to let it work. heat is 100% floor. ac/vent is 80% dash and 20% floor.

 

[Jwernatl]

I must b e an idiot - I have 1987 V10 350 w/ac -

My heater core popped so - I did what I do - pulled the box

What's the trick to get the heater CORE out? I took the top 4 screws out that were around the heater core section - from the video I saw on line - its supposed to pull out. (Im thinking the video was an earlier year)--

So then I pulled the 5 screws that were holding the rest of the lid. But no good. Do I need to pull rods maybe? How do I open this up?

Because, Im sure it's best to redo the entire box. I've tried to find steps for a break down - what am I missing?

I do see a few things...

1. 2nd pic below...my blend door has that piece broken (I know we can replace with a billet one) but, any other ideas or tricks to fix - mend and or make stronger??
2. 3rd pic below....the foam on one of the doors on the back is trashed - I want to replace... but with what?

Thanks all for any help...

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[Craig 85]

That cover comes off the top of the core. In your picture I see at least one more screw installed. I can't recall if the rod needs to come out.

In picture #3, I used the felt furniture pad material I got at Home Depot. I used the 3M brand (4"x6"), but you might be able to use the smaller style Everbilt brand (2"x4"). It doesn't take much. I reused the staples from the OEM unit to attach it

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[Jwernatl]

Hey Criaig, I just wanted to let you know - this worked great. I used, very close to the pic above, a version of the felt pad - I actually had an extra pad (from years ago) in the 'junk drawer'. I also re-used the original staples - It worked GREAT.


Oh, and. from above.. "That cover comes off the top of the core. In your picture I see at least one more screw installed. I can't recall if the rod needs to come out"

You do have to pull the two rods out - once I did that, ez-pz. it's now perfect. I tested the doors/vacuum etc before putting it all back together.

Thanks again for he help -