Heater Core Box Reassembly
 

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.

https://i.ibb.co/VvyFZfD/20230217-181758-HDR.jpg

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.

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

https://live.staticflickr.com/65535/...30f991df_h.jpg76 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.

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

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

https://live.staticflickr.com/65535/...ee8e385c_b.jpg20230218_114804 by Ben, on Flickr

https://live.staticflickr.com/65535/...0d76fdd3_b.jpg20230218_114819 by Ben, on Flickr

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...

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.

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.

Care to sell one to me? :D 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.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

https://live.staticflickr.com/65535/...464ed718_b.jpg78 AC Vacuum heater diagram by Ben, on Flickr

https://live.staticflickr.com/65535/...fb90b5d3_c.jpgFirebird cowl air recirculation vent door vacuum setup by Ben, on Flickr

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.

you didn't really hijack anything, I'm still trying to figure out how to reassemble this heater box, too!

I'm pretty sure I've forgotten to re-install a spring or two somewhere. Is there supposed to be a spring at the defrost door? How does it attach?

There's a return spring already built into the arrangement of rigging where the levers are, where cable attaches. There's also a return spring that holds the defroster/floor door sealed when not under vacuum.

Thank you, I think I forgot that second one. Somehow I need to figure out which of the leftover springs goes there...

I really wish there was a reassembly DIY with pictures somewhere. This heater box was a mess when I got to it, so figuring out how it's supposed to go back together is a nightmare.

Mine is out and I didnt take anything apart - what photos do you need?
Attached are a few photos of the levers and spring for the defrost door. The side of the spring on the defrost door that you cant see attaches to an existing hole on adjacent side aluminum plate.

I'd love to know which spring is used to keep the defrost door closed when vacuum isn't applied to its canister. That's the long door that's mostly horizontal. I also need to know where it attaches to that door. I've figured out where the other end of the spring attaches on the sheet metal part of the housing.

I edited my last post with photos.

Good pics. See first and 2nd for spring on door flap that keeps it shut, vacuum pulls it open. The staples normally hold a sponge foam seal onto the door, always long gone.

3rd pics you can see the spring at top right on the pivot post.

THANK YOU! That helps enormously

I am trying to figure out the vacuum system as I do this. Perhaps someone can help me with what is necessary and what is not.

I have a 403 that runs pretty strong but I acquired it with much of the vacuum components disconnected as an aftermarket edlebrock aluminum performer manifold and 750 Holley carb were added.

I have found in fixing all that the vacuum advance on the distributor is not hooked up. Nor is the charcoal cannister, any of the vacuum lines associated with the air cleaner (except the main line down to the valve cover), or the small vacuum line that controls the AC system that is supposed to have a check valve in line somewhere.

After market chrome valve covers are also added.

I have attached two photos of the basic 403 vacuum system. The first photo is one that I found for reference - the second photo is edited to show what is not hooked up on my system (circled in red) - is not hooked up - the yellow shows only the manifold vacuum going down to the transmission and that is all that is currently hooked up to the manifold vacuum.

My brake booster is to the rear base of the carb and noted in Blue on the second photo.

I have to fix the vacuum system - I have a vacuum port open on the front base of the carb that I believe to be ported. I think I need to plug that line and run the distributor, transmission and AC controller off of the Manifold Vacuum - is that correct?

Where do I connect the check valve and the AC controller vacuum line to the system?

What is necessary on all the other components not hooked up and what is the simplest way to include them if they are necessary? Can I bypass or remove the cannister?

Do I need to start a different thread with this topic?

Please advise.

Thank you.

Those are all engine and emissions diagrams, the simple vacuum for dash controls come off the rear intake runner port.

Start a new thread, that sounds really messed up. Whoever carried out the carb swap obviously didn't know what or why they were doing it, which is nearly every carb swap.

https://live.staticflickr.com/65535/...95fb5d4e_b.jpg403 olds intake vacuum checkvalve (2) by Ben, on Flickr

https://live.staticflickr.com/65535/...0517715e_b.jpg403 olds intake vacuum checkvalve (1) by Ben, on Flickr

Right. All the heater box vacuum comes from that vacuum check valve, and gets distributed through the interior by the climate control unit.

What you're referring to is the underhood vacuum system, which is completely separate from the heater box and climate control. In my case, I eliminated almost all of it, with the exception of a vacuum switch that sends ported or manifold vacuum to the distributor (depending on coolant temperature), the PCV valve (which goes to a dedicated port on the carb), and the charcoal canister (which j'ai goes to a dedicated pet on the carb). Beyond that and the heater box, I've blocked off all other vacuum because I no longer run a vacuum brake booster or any other emissions systems.

If you need info on the underhood system, you'll need to start a new thread in the Street Engine category of this forum

Thanks guys, for your help.
I am not running any emissions either - 403 with better cam - headers - internals unknown but runs strong. Rear end has been upgraded to approx 3:25 gears. I just want to clean up the vacuum system so it is correct for what I have.
I will start another thread in the street engine section.
Thank you.

Alright, I'm finally just about done and ready to put the heater box back in the car (engine took precedence for a bit). Almost everything is solved. One last question, what attaches to this screw?
https://i.ibb.co/ZhRvGnX/20230611-111616-HDR-2.jpg

That wouldn't ground it anywhere, though. That screw just threads into plastic

Might be a wire harness or vacuum line clip... but if it is, I misplaced it

Try this, loop retainer for the vacuum line that goes to kick panel and cowl door. It's just folded over and screwed.

https://live.staticflickr.com/65535/...d978079f_b.jpg20230612_021013 by Ben, on Flickr

https://live.staticflickr.com/65535/...2585a10c_b.jpg20230612_021613 by Ben, on Flickr

Ah hah! That's the one, thank you!

I fixed all vacuum issues and installed my heater box and everything seems to work good.
I have new carpet in and the dash and behind dash duct work is ready to be installed. Before I proceed.....

I noticed on the attached photo of the duct schematic that there looks to be a gasket of some sort between the heater box and the cowl evaporator box. There was nothing there when I removed the heater box and is that missing seal necessary?

The box was kind of a bitch to install and the lower nut is hard to get to with headers so I would rather not remove the box again to put in a seal if not necessary.

Please advise.

Thank you.

That's the firewall seal.

I am missing something in the description - I did not have this when removing the heater box. Is this a removable seal and is it located on the under hood side of the firewall.

The heater box is under the dash so the seal is also on the dash side to seal heater box to firewall. #3963725. There's nothing on the engine side, just the heater core pipes coming through, each with a sponge seal around them as well.

Some sell a reproduction, otherwise just use close-cell neoprene with adhesive backing on 4 sides.

Random ad.

https://www.chicagomusclecarparts.co...amaro-trans-am

I consider it an important part of the installation. If it wasn't there before and you didn't mind, then I guess you can leave it that way. It significantly improves the performance of the heater, and especially the AC if you have that, plus it really cuts down on noise and smell from the engine bay. My old one was damaged from old age, so I made one by cutting out a rectangle from an adhesive-backed foam insulation sheet
https://a.co/d/1OXXmdk

Some more diagrams.

https://live.staticflickr.com/65535/...93a27a6d_h.jpgFirebird AC heater box ducting evaporator case assembly diagrams (1) by Ben, on Flickr

https://live.staticflickr.com/65535/...63619573_h.jpgFirebird AC heater box ducting evaporator case assembly diagrams (2) by Ben, on Flickr

https://live.staticflickr.com/65535/...f10be272_h.jpgFirebird AC heater box ducting evaporator case assembly diagrams (3) by Ben, on Flickr

Not shown in that diagram, the AC box in the engine bay uses that gooey butyl rope seal around the periphery that presses up against the firewall, and between the two halves of the box. There's a channel in the mating surface to accommodate it. Those seals are VERY important, otherwise the AC performs like crap.

I only added pages for what was being discussed. Yes, the case is right next to the exhaust, any gaps introduce more heat straight into the AC, and cabin, fumes, sound, ants...! Any gaps will allow the fan to suck air from the easier route, the hot air gap next to it rather than through the evaporator of cold air.

I'm reassembling my heater box right now as well due to an original heater core leak, I went with Ames' copper/brass repro and it seems to be a quality unit and held vacuum when I tested it.

Chicago Muscle Car parts does have the seal kit in stock, I bought it myself and it looks good. Only thing is, there is not adhesive on the seals so you need to apply spray adhesive. Not really necessary for the heater core pipe seals since they fit snugly around the pipes, but the square gasket definitely needs spray seal. Just bear in mind that Chicago Muscle Car parts doesn't do online orders, you need to call them. They ship pretty fast.

As expected, my orange vacuum tube going to the heater side nipple of the push/pull actuator was crumbled to nothing; and the actuator itself was so rusted on the inner nipple that same orange line was hooked to that it was beyond serviceability. Had to replace that, too.

The mounting stud that is clipped onto the corner of the heater box with the integrated ground strap was also bent beyond serviceability on mine, luckily they sell repros of it on eBay, but without the ground strap, so I got a generic groundstrap of appropriate size from Falconer Electronics. I had to relocate the large eye that used to be part of the mounting stud to the lower mounting screw instead (the one you unscrew from inside the car). The ground strap is very important.

Also make sure to replace the foam layering on the defrost diverter door. From the factory, the foam layer is stapled on (thus the staples you see). I had to pry off the staples and install adhesive foam I got from BlendDoorUSA. It's high end stuff that isn't biodegradable like the stock stuff was. And yes, you do need to cut out the two holes in the foam to match the two round holes in the diverter door. Those two holes are the "20%" of air the windshield and/or floor vents get respectively depending on the settings that the service manual is talking about.

While you're at it, you may want to replace the heater hose nipple at the rear of the cylinder head if you're running a Poncho motor. The later design uses a rubber restrictor rather than the bimetallic coil the older ones used to restrict coolant flow to the heater core. When I removed mine, the rubber was missing and that's probably because it had disintegrated over 45 years as it was the original nipple. Without some degree of restriction, the heater core is subject to earlier failure due to the slugs of water overstressing it during heavy throttle. Another option is to just place a .200 restrictor inline somewhere in the inlet heater hose going to the core from the back of the head. That's what they installed on the police car packages.

Probably all engine types had their version of the retrictor fitting in Firebirds since there was no heater tap valve. I was only just posting info and pics of the Olds version on another forum.

I appreciate all the info- As much as I would rather not, I will be pulling the heater box out and sealing it correctly.

By the looks of the helpful links and photos, I am missing the seals around the water intake pipes also.

I noticed I only have one seal for the intake tubes - I have the one that mounts to the housing under the hood. It looks like I need to have two other round seals that slide over the intake pipes sandwiched between the box and the firewall.

You guys are very helpful

Thank you

Broken stud on heater box
 

On my 79 TA, I finally found time to remove the newly installed heater box and I installed a seal against the firewall.

As Murphy would have it, I broke the lower stud behind the passenger side head when reinstalling the heater box. I didn't think it was that tight when the stud broke but obviously - the king of overtightening strikes again.

Does anyone have any ideas on finding a new stud?

Any recommendation on just leaving it with only the two mounted studs and nuts. I am sure you the seal will not be uniform around the blower housing with only two studs holding.

Has anyone delt with this and what is the fix?

Does anyone have a torque spec or recommendation on the housing stud nuts?

Thanks guys.

Which stud are you talking about? One of the two that are integrated/welded into the metal frame of the heater box, or the one that is clipped onto the outer edge and has the integrated ground strap?

If it's the latter, they reproduce it and you can find it on eBay. I had to replace mine with this one because I bent mine beyond accepting the nut along the entire thread: https://www.ebay.com/itm/393981832146

The only problem with the repro one is that it doesn't include the ground strap, which is extremely important since it prevents the coolant from degrading the heater core via electrolysis. What I did was just purchased a generic groundstrap (roughly 5-6") and relocated the large eyelet to the bottom mounting screw for the heater box (the ones with the teethed washers that you access from inside the car).

As for the ones that are part of the metal frame, there is a guy on YouTube that goes over replacing the heater core for his 1980 (or 1981, not sure) and he runs into the same issue and describes what he did.