[GoreMaker]

Is there a grommet that goes over that hole at the above the vacuum canister? Or does that stay open like that? I realize a rubber line will come out of it to connect to a vacuum tube.



Also, for the door that that vacuum canister actuates, I can only adjust it to seal at one extremity of the vacuum canister's range or the other, but not both. Should I bias it to seal in heater mode (vacuum applied to yellow tube) or NOT heater mode (vacuum applied to white tube)? The pontiac assembly manual doesn't appear to clarify.

[Trevor78]

It has a rubber grommet that slides in from the side, often dried out and hard.

76 Camaro AC heater box6 by Ben, on Flickr

I'm not sure what you've tried, and can't recall how mine was which is modified anyway, but there's adjustments in the length of the control rods, location of the pivot brackets, and the manual cable length from the dash. From memory one is closed under vacuum but fights the spring tension so will open again just sitting there.

[GoreMaker]

Thank you! It seemed odd to leave it open when most of that area is sealed

[Trevor78]

I just dragged out a box of spares for a pic. No part numbers cast into it.

20230218_114804 by Ben, on Flickr

20230218_114819 by Ben, on Flickr

[GoreMaker]

Huh, doesn't appear to be anywhere in my box of parts that I removed. The hose is there (and in dire need of replacing), but not that grommet. How annoying...

[GoreMaker]

Originally Posted by Trevor78

I'm not sure what you've tried, and can't recall how mine was which is modified anyway, but there's adjustments in the length of the control rods, location of the pivot brackets, and the manual cable length from the dash. From memory one is closed under vacuum but fights the spring tension so will open again just sitting there.

This specific door is held in place in the middle of its travel by a spring. It's sprung in both directions. Vacuum on the yellow tube (Off, Heat, Defrost) directs all air through the heater core. Vacuum on the white tube (Max, Norm, Vent) bypasses the heater core. No vacuum on either tube (Bi-Level) causes air to flow through both paths because the spring keeps it there. The vacuum canister doesn't have enough total range to seal the door completely in both directions no matter how I adjust it, so I'm wondering if it should be sealed when bypassing the heater core, or when flowing through it. I'm leaning towards sealing off the heater core so that air from the evaporator doesn't get heated unnecessarily when the AC is on. It shouldn't really matter if a small amount of unheated air gets blended with the heated air when the heater's on.

[GoreMaker]

Ah hah, just got confirmation from the service manual. When AC is on, there should be no flow from any vents except the AC vents. So that door needs to be adjusted so it's sealed with vacuum on the white tube, as I suspected.

[GoreMaker]

Originally Posted by Trevor78

I just dragged out a box of spares for a pic. No part numbers cast into it.

Care to sell one to me? I can't find one anywhere, used or new. It's fine if you'd rather not, I can just make something that'll serve the same purpose, but I figured I'd ask.

[i4abuygto]

I am in the same position as you with no rubber grommet to seal the opening for the rubber vacuum line for the yellow tube. I am just going to use a piece of tin shaped to a 90 bend with sealant between the tin and the box.

Ah hah, just got confirmation from the service manual. When AC is on, there should be no flow from any vents except the AC vents. So that door needs to be adjusted so it's sealed with vacuum on the white tube, as I suspected.

I bench tested my canisters with approx 7 - 10 lbs of vacuum and the door closes completely in both directions. I did have to clean out the yellow side of the canister with a welding tip cleaner as the rubber hose was broken off and some surface rust corrosion clogged the vacuum. At first it would not pull any vacuum as the inlet was clogged. Just make sure your canister is pulling both directions. The biggest air bypass gap with the door on mine is beyond the door hinge mounting pivot point (appox. 1/16" inch) and that is just in the design of the system. I am a little concerned about the surface rust corrosion on the yellow tube side of the cannister as it is inside the box and exposed to more moisture - Pretty rusty but all works well so I will probably just treat the metal and button it up.

I will be lubing all pivoting points with a dry lube (doesnt attract dust or dirt) before a put it back together.

[Trevor78]

Haha I'm in Australia but feel free to have one! I picked up several junk heater boxes years ago, just for vacuum lines and retainer spares.

[GoreMaker]

Originally Posted by i4abuygto

I bench tested my canisters with approx 7 - 10 lbs of vacuum and the door closes completely in both directions.

Weird, mine absolutely will not. It's a brand new vacuum canister, because I wasn't comfortable with how much rust was on the nipples of the old one. Was worried they might break off. I checked with the old one, and the travel is the same as with the new one. The door just won't seal in both directions no matter how I adjust it. Everything is lubed, I can flip that door easily by hand for its full travel, the vacuum canister just doesn't have enough range to get the door to seal on both directions, only one or the other

[GoreMaker]

Originally Posted by Trevor78

Haha I'm in Australia but feel free to have one! I picked up several junk heater boxes years ago, just for vacuum lines and retainer spares.

Oops! Yeah, you're too far 😂 I'll just use a pair of sealing foam layers to accomplish something similar

[i4abuygto]

I ended up finding the rubber grommet dangling on the vacuum line inside the car.
In great shape - Looks like it was never installed right.

[i4abuygto]

Hello Goremaker,
I have another thread going about electrical connectors I need to identify.
If your under dash is all apart, perhaps you could take a few minutes and check the radio area of your harness and see where the gray connectors with the Black, white, gray and pink wires (pink wire goes to another gray single connector a few inches away) and what they are connected to.
These two connectors are open under my dash and I would like to know their identity before I close up.
If your ducting and all is still in place and you can't get to the wires, please disregard my request and thank you for you consideration.

[GoreMaker]

Originally Posted by i4abuygto

Hello Goremaker,
I have another thread going about electrical connectors I need to identify.

Oops, sorry I never got back to you on this. My interior is completely stripped, and the heater box is the first thing to go back in before tackling the aftermarket wire harness, so I'm afraid I have no insights to provide.

[GoreMaker]

Originally Posted by i4abuygto

I bench tested my canisters with approx 7 - 10 lbs of vacuum and the door closes completely in both directions.

Turns out I was wrong. The replacement canister I bought only has 0.63" of total range, while the OEM canister has 0.9" of range. This is why I couldn't get the door to seal in both directions. I ended up cleaning and sanding and painting the old canister to get rid of the rust on it, and now it looks better than new and the door seals in both directions.

[i4abuygto]

My interior is completely stripped, and the heater box is the first thing to go back in before tackling the aftermarket wire harness, so I'm afraid I have no insights to provide.

Good to hear that you got the vacuum working at full range on your heater box.
I am in the same position- dash and interior is completely out of the car and I am fixing all electrical on the way up now.
I figured out all of the connectors I had questions about - radio and rear defrost related.

[i4abuygto]

79 Trans am 403 engine.
Before I install my heater box I wanted to test all the vacuum canister operation with the AC controller hooked up. Using a vacuum pump system, I applied vacuum to the controller through main feed from the engine vacuum line as it would be with the engine running.
While operating the controller, all seemed to work okay except the cowl vent door did not seem to move. The cowl vent door is the one that the vacuum is fed through the firewall above the heater box and one cant see any canister operation (see photos). The door appears to stay open and not move with the shared passenger side kick panel canister as they share the same vacuum control circuit.
That circuit only appears to pull vacuum on the MAX control setting and I am getting vacuum at the kick panel canister. Is that correct and do I need to even be concerned about the cowl vent door operation.
I would like to know how it all works before I install the heater box and put the dash and interior back in.
Please advise if you have knowledge about this.
Thank you.

[Trevor78]

Recirculation mode or Max, will close the cowl vent and the kick panel door. There's a vacuum diaphragm under the cowl door, that's what the bulge is for. Unbolt the door surround and remove, suck on the tube and see what happens. May be all rusty and junk or a cracked hose. Check the condition of the cowl block-off seal while there, can now buy them new, although just a piece of curved sponge rubber.

78 AC Vacuum heater diagram by Ben, on Flickr

Firebird cowl air recirculation vent door vacuum setup by Ben, on Flickr

[i4abuygto]

Thank you for the info on the cowl door and the vacuum diagram - very helpful.

With your attached vacuum diagram, I noticed I need a check valve in the system. I found a diagram for the vacuum routing under the hood and showing the check valve in the system. The 403 I have has an aftermarket intake with Holley 750 carb so I will likely need to pull the vacuum for the AC controller off of that carb.
Most of the stock vacuum system under the hood has been butchered with the intake modification so I will have to figure that out.

I acquired the car with a bad heater core and nothing working in the AC heater or blower system. I had to learn the entire system to fix wiring and ducting. Now I have the system working with the high speed fan working and I just have to figure out the cowl door and I should have the basics done. I still need to rebuild the AC system forward of the firewall. After the dryer, all under the hood components and condenser, for the AC system are missing.
I did acquire an AC wiring harness and AC controller harness that is not all chopped up with good connectors. Looks like I need the AC compressor harness forward of the firewall but I will get that when I decide if I am going stock or vintage air on the system.

Hopefully I can install the dash and interior soon.

I did not mean to hijack this thread but it is all related to the heater box re-assembly and install - thought it better here than a new thread about the same topic.

Thanks all for your help.