Getting lots of hear inside the car and read a post by vettfixr concerning the heater sucking in engine bay hot air via a plenium. I have looked and looked and can not find this plenum which is located under the car, Supposedly most of the heat can be eliminated by sealing it off--leaving a small hole water water drainage. There was only one picture posted which was a cutaway--which I have looked at but still can't find it. Can some please post some pictures of the plenum opening so I can find it? Thank you.

Dying from the heat.

 

I am not aware of a plenum under the car, so you can quit worrying about trying to find one. The thread you reference may have been talking about the areas at the cowl at each end of the wiper trough. On non-air cars, these are open to allow fresh air through the interior vents. On factory air cars, the left side vents are sealed off and there should be a flapper door on the RH side.

Check the condition of your hood weather stripping. When in good shape, it's supposed to keep under hood hot air from reaching the cowl area.

 

Here was the post and it was also on digital corvette and a picture


Eliminating Cockpit Heat in a C3
By IBxAnders - April 21, 2010
0 COMMENTS
Like most of you I\’ve battled the problem of cockpit heat. I think
I\’ve finally found a problem in my 74 that may be common to a lot of
C3s and which may cause heat to come in to the cockpit no matter how much
insulation or sealing is done to the heat/AC system. Over time I\’ve
noticed that I always got an \”engine\” smell in the cockpit. I figured
it was air coming out of the hood and being drawn into the heating system
through the air intake in the wiper trough or air leaking into the system
through the heater box. I put a wiper cover on earlier this year and I
could see that the hood sealed really well in this area so this
shouldn\’t cause a problem with air leakage past the gasket. Since I
pulled my heat/AC system out last winter and resealed everything I
discounted this as a cause for heat leakage also. When doing the heating
system I also installed a shutoff valve for the coolant. I also insulated
my entire cabin so I\’m not getting heat through the floorboards or the
body. This left the air intake on the system as a possible source. I
removed the right hand dash pad and kickpanel which exposed the flapper
mechanism for the inside/outside air control. I removed the vacuum motor
and flapper mechanism by unbolting the two bolts that hold the motor,
moving it out of the way, and unhinging the flapper. This is done by
pulling down the top spring loaded pin, pushing the door into the
fenderwell and twisting it so that it can be removed from the inside of
the car. I then started the engine with the hood closed and the heat/AC
off. I felt hot air coming into the plenum from the engine compartment.
This plenum is secured with the same adhesive that holds the rest of our
body panels in place and like those the adhesive will dry and crack over
time. Anyone who has dealt with stress cracks on the fenders can attest to
this. Remember also that air leaking into this plenum will be coming
directly off the exhaust system and with headers the problem is
exaggerated. To seal this plenum I used windshield sealing caulk. You can
get this at your local parts store for around $5 a roll. I used the caulk
to seal around the entire perimeter of the plenum, or as much as my arm
would reach since you\’re working through the flapper hole. The most
important areas to seal are the forward and lower area since that\’s
where the majority of the heat will come from. The rear area is sealed
against the forward door jam and really shouldn\’t leak hot air. After
doing this I repeated the test with the engine running and felt no heat
entering the cockpit. I reinstalled everything to complete the job.
I\’ve only driven the car twice since then but I can tell you that there
was a vast improvement. I took the car to work on a day when the
temperature hit about 85 degrees. Before the fix I would have had to have
the AC running or the heat would have been unbearable in the footwells and
even worse with the t-tops off. I ran the car home that day with the
t-tops off and the footwells were no hotter than the rest of the car.
I\’ve also noticed that the AC tends to run a little cooler by not
having to fight the heat coming into the system. So far I also haven\’t
had that \”engine\” smell anymore. I\’m hoping that as I use the car
more, in different situations, I\’ll be able to report more benefits
from this fix but until then I thought I\’d give a heads up to everyone.
For details on the cockpit insulation go to my website. You\’ll see the
article on insulation and also what you have to remove to reseal the
heater box.
UPDATE 9/12/03: Since posting this topic in the C3 forum over a year ago
I\’ve had time to live with this fix and I can tell you it\’s
completely eliminated the footwell heat common to C3s. I\’ve also
recommended this fix to others who have had similar success. One tip that
I left out in the original post was to put a soda straw through the bottom
of the plenum until it sticks out below the rocker panel. Seal the plenum
all around the straw and when you\’ve completed the sealing pull the
straw out through the bottom of the rocker panel. This leaves a drain
hole that will channel water in the event that it enters the plenum.
Other than that it\’s an afternoon fix that really pays off. Good luck.

 

That post is discussing a poor or broken seal between the body fenders and the interior vent structure. If you've eliminated everything else this would be a good last resort. Not sure how you'd go about sealing that area without removing the hood surround & fenders though.
Your best bet is to make sure your kick panel seals are in good shape and that your heater damper is functioning.

 

From the post, I thought this was a defect that was present in all the corvettes that needed to be sealed. Maybe I just misunderstood the post.

 

Hi w,
If you're getting hot air through the plenum I believe sealing the flapper door more carefully is the solution available with the front clip on the car.
Regards,
Alan

This is the interior side of the vent door shown in the photo you posted.
It originally has a foam seal around it's perimeter.
This is a no a/c car.

 

Alan:

As always THANK YOU for the picture and help. Paul