I'm in the middle of LS7/570, Tremec T56 Magnum F swapping my 28.200 mile, 1987 IROC Z. I'm not the original owner so I don't really know what's been done to the car before but I do know that the heater core was swapped out for an aluminum replacement in its past.

I have the heater/HVAC box out because of:

1. Extensive under-dash work
2. Refoam the blend doors

I removed the AC and defrost doors, scraped the deteriorated foam off, wet sanded with 320 grit paper and then primed and painted with SEM paints. Here are a couple of pictures of the redone AC and defrost doors:


You can see the new foam below the AC door.



Both doors now have new foam, front and back.


Here is where I start to wonder if something is wrong/missing. With the doors mounted back in the box, if I manually open the doors to where they cover the aluminum heater core, I big portion of the heater core is still uncovered which seems like it would let a lot of heat into my stream of AC evaporator cooled air:


That's a lot of heater core that is not covered. I'm sure with circulating hot coolant in that heater core, some heat is going to heat up my cold AC air.

It just seems to me that the heater core should be completely covered and isolated from the incoming, evaporator cooled, AC air. Am I missing something that should be covering the heater core?

Maybe the original engine's (350TPI) heater valve as seen in the next picture keeps hot coolant from flowing into the heater core during AC operation?

If need be, I'm sure that I can incorporate this heater valve into my LS7 swap.


I did do a search on this forum and I couldn't find an answer to my question of whether or not the heater core should be fully covered. Please let me know so that I can move forward. Thanks, everyone!

 

If I'm not mistaken, the doors you're touching are mode, not blend. The lower door is for floor, the top for center outlets, and combined they provide either bi level or defrost as a default. The blend (temp) door is a solid door.

 

ratfink, you are correct. The two doors that I'm touching are upper and lower mode doors and the blend door is called the temperature door which is what you said. I've changed the title to this thread to reflect the correct names.


This is from my 1987 Camaro shop manual.



I'm still looking for confirmation that the heater core doesn't have any additional covering over it. See picture #3 in the first post.

 

If that's the case, yes they are correct. They seal against the housing your hand is through. When they're open it allows air to flow based on how the temp door is positioned. I don't believe there's any other passage for them to seal to

 

Yes. I was pretty sure that the mode doors are positioned and operating correctly. My concern is the amount of hot heater core that is open to the cold, air conditioned air as can be seen in the picture below:



In the air-conditioning mode, one or both of these doors should be in the position in the picture. The cold air will come through the temperature door and then from the right side of the picture and flow where my hand is sticking through and then through the vents. My concern is the cold air flowing over the hot heater core. I do understand that when the AC is on max, the heater valve should keep hot coolant from flowing into the heater core. Also on max, the lower triangular shaped door should be closed (the door would be where my hand is) forcing all the max cooled air out of the dash vents.

 

I believe this is the case. The upper/lower door only directs the air to their respective ducts, but there's nothing that covers the backside of the heater core. The blend door only covers the front side.

 

Thanks, pirate for your reply.

I watched a youTube video of a heater core replacement. The guy's heater core inside the heater box looked exactly like mine; no additional covering over the core itself other than what the two mode doors cover like in my picture in post #5.

According to what I read in my shop manual, the heater valve that I have circled in the last picture of post #1 shuts off any hot engine coolant to the heater core when the AC is selected to max. Keeping that hot coolant out of the heater core should result in cooler AC temperatures. This is a big deal in Houston summers! I wasn't originally going to use a heater valve in my LS swap but now I'll definitley plumb one in. I think I may try an electric valve. On the other hand, the OEM valve is vacuum operated. Maybe it's more reliable?

 

Vacuum operated heater shut off valve: ACDelco Heater Valves 19193204

 

Where did you get the new foam from? I've been looking for foam for my blend doors as well

 

Synthetic Polyether Open-Cell Foam with a 3M peelable adhesive

This is really pricey stuff. They also tacked on $13 to ship lightweight foam. Really pricey but this is probably the best quality foam that you can buy. Did I mention that it's really spendy?

 

I know this is old, but I am in the process of rebuilding my system too. My doors are exactly like yours. My 83 never came with a water valve and it cooled OK. With that big of an opening I'm sure I wouldn't have gotten anything close to cool air. Maybe we're not looking at something right.

I need foam too but I also need the 1" foam where the this assembly attaches to the dash. Polyether foam is hard to find. I haven't found a site where I put it in a cart and buy it. They all want me to request a quote. IOW, a large minimum purchase!

 

69-er, thank you for posting your picture. Mine looks like yours with no foam in the same place that your HVAC box doesn't have foam. I've been trying to post a picture of mine but something is up with this website and the picture will only load up to 90% and stop. I tried to post the picture via my Chromebook and my iPhone. Both freeze up at 90%. It must be TGO having some type of problem right now.

 

The website is allowing me to post a picture now. You can see that my HVAC box's foam looks like yours. There is no foam on one edge. With yours and mine not having the foam, I guess that's the way they came from the factory.

 

Good to know about the foam on the edge.

I see indentations in your foam showing that it looks like it's been installed but it looks new. If so, did it come from Blend Door USA? All I see is 5/16" thick. I am having a hell of time finding polyether foam they use, at least in small quantities. I bought some regular polyurethane white cushion foam in town but I can't be sure how it will hold up.

I have a template ready to go.

 

The thick foam in my picture is OEM foam. My car is a low mileage (28,xxx miles) car and this foam is in good shape. The thinner foam on the doors was all deteriorated due to age.

Yes. I don't remember Blend Door USA having anything thicker than the 5/16" foam which works perfectly for the HVAC box doors if you can get past the sticker shock for the foam.

For thicker foam, I bought some from my local Home Depot. So far I haven't used any of it and maybe it was a wasted purchase. It didn't cost much at all. Probably not the longest lasting foam but it'll probably be good for 10 years or so.