I have a 1972 convertible.  I can't seem to keep hot air out of my car.  On a nice 80 degree plus day, the last thing I need is hot air coming from what seems to be every vent in the car.  Even with the controls in the off position I still get air.  I have factory Air also.  I've had the dash all apart several time.  I've tested the vacuum actuators and they all seem to work.  I'm just wondering if the Heater Box is working correctly.  I also am not getting much air coming from any port (Vent or Heat selection).  The defrost seams OK. 

By the way Dave I really like the color of you car.  

Dave Welcome to the world of hot floors on C3's! There are many things that can cause this to happen but the biggest issue I have found is the heat from the exhaust pipes that soaks into the firewall and floorboards and passes to the passenger compartment. When I bought my first vette, my first roadtrip was an hour long  to corvettes at Carlisle on a hot 95* summer day. I made the mistake of taking my wife along and the floors became unbearable! Our feet were on fire. Needless to say she made up her mind that vettes werent for her and hasnt changed her mind since! Anyway, I tried many things but the best fixes were buying a product called Lizard skin. I removed the carpet on the interior and sprayed the floor boards and interior firewalls with 2 layers of the lizard skin. Then I bought the thin bubble insulation at Lowes that has foil on both sides and glued that on top of the lizard skin once it had dried for about 48 hours. Then re-installed the carpet and seats. Now the carpet is a little tighter getting back in but what a difference that made. The key is to get the insulation and lizard skin up under the dash as far as possible. On my 72 that I redid I had the dash totally out. Made it easier to get complete coverage. I also did the underside of the floor boards and firewall on the 72 then covered with Por15 paint. That makes the car almost normal! If you decide to try the lizard skin you will need a special gun to spray it with. Don't buy one as I have one that I would be happy to lend you to do yours once I get it back from another member who is using it. If I can help you in any other way with this let me know. I have many pics of mine as it went back together.
Best of Luck
Rodney 

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If you don't have a manual shutoff on your heater hose in the engine compartment, that is one thing I found that greatly reduced the heat. My 78 had a vacuum controlled shutoff under the hood but it was almost useless in preventing heated fluid from circulating. I originally looped the heater hose from the water pump right back into the engine block to shut off the heat.  The flapper door that was mentioned by 82 ce was my second biggest form of cockpit heat entry. You can see it the door back in the corner looking by the passenger wiper area. At least feel it moving if you apply a vacuum source. Mine was operating but not fully closing due to it rubbing the side of the chamber. A lot of engine heat was going directly into the cockpit. Vaccuum actuator was working fine, just had to manipulate the door to prevent it from rubbing. I also resealed the AC evap box to stop heat. A lot of sealant was missing from the firewall where numereous hose and wires enter . The insulation in the floor as mentioned before is a must do to keep the floor heat to a minimum. Hood seals and a lot of detective work. Their is a seal that goes above the tranny and firewall also. I found that didn't seem to help much. Not one big thing doesn't, just a lot of little plugs...

Thanks everyone for the great replies.  It will give me some ideas to check out.  I did a complete frame off restoration on this car several years ago and when doing the restoration I included a layor of rubber sound deadener and foil backed carpeting.  I also installed a preformed insulation mat for the firewall.

 On an A/C car, when you roll the thumbwheel to "Vent", you will NOT get any air out of the normal vent locations. "Vent" air will only come out of the lower vents, on the lower edge of the dash, no matter what the fan is set to. The fan only controls airflow when in heat/defrost, or A/C modes.What yo may have is a vacuum problem, or a diverter door that is not completely working, and allowing more hot air from the heater core to enter into the cabin, which would be made even worse by opening the "Vent", since in Vent mode, the air coming into the cabin is comming from the base of the windshield....which is heated from engine heat. It's a no-win situation, unless you want to completely disassemble the dash/HVAC system, and get all of the ducts, and firewall sealed properly....and make sure all of the plenum doors are opening/closing properly.

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

On a 72 there is not a water control valve, water has to go through the heater core. That's the way mine is. I took the heater box all apart and replaced the door seals and that helped on shuting off the heat from coming into the cabin. You will need a heater box seal kit and a heater door kit, also you might went to replace the heater core while you have the heater box appart. You can get the parts you need from most of the Corvette parts suppliers. Good luck

I'd like to see any pics U have of ur vette insulating job....  Im trying to get some heat going for this winter, but I'd like to stop the extreme heat in the summer too.  I have seen the Power block guys use that lizard skin stuff pretty frequently....

Here's some pics of a '72,  using the foil backed insulation..

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

thanks