I have a 70 350/350 and I am trying to revive the AC.  However, I feel that is futile given the amount of heat that comes throught the vents.  It comes through the lower heater vent as well as the ball vents and middle dash vent.  The air is so hot it actually seems hotter than if the heater were on.   The duct work at your feet gets so hot you can barely touch it.  Also, the amount of air that comes out is relative to the speed of the car.  At a standstill, the amount of hot air coming out of the ducts is very little.  At 60mph, the amount of hot air coming out of the ducts is roughly the equivalent of the fan being on med-high.  This hot air ALWAYS comes out after the car warms up.  It does not matter what setting the controller is set on. During the hot days of summer, the o8nly way the car is bearable is if I stuff rags into all the duct openings to block the hot air.  This does not cure the scorching heat at my feet from the hot duct work. 

Steps I have taken so far-

*Tried to seal the right side plenum as best I could.  I did not feel any separations . I used the windshield gooey strips for a seal.  Unfortunately, I am a bigger guy so my reach up through that little hole was limited.

*I have put a shut off valve in the heater hose to keep the hot water from circulating through the heater core.

*I have checked all the vacuum doors (that I could get to) and the system seems to be functioning (including the upper and lower plenum doors) The only one I did not get to was the outlets door because it is hidden behind the instrument cluster.

*The hood appears to have a good seal so I do not think the engine heat is leaking through the hood into the fan intake.

I assume that this hot air must be from the engine compartment and is getting into the ductwork soemhow.  I do not think it is the result of poor insulation from the dash/firewall.  It is simply too hot and the iar flow is too great for it to be just a transfer of heat through the plastic.

My questions-

*Where else could the engine compartment heat be entering the duct system?

*If it is the plenum on the passenger side, what is the shape of the plenum and where is the most likely separation?  

Is the increase of hot air flow due to speed a natural part of the Astro Ventilation?  Remember that the hot air flow happens even if the controller is set to off.

Thanks for any advice you might have!

Mickey 

If your 70 is like my 68 the hot air from the floor vents are directly connected to the engine compartment which allows the hot engine air to enter very well. Good design for Alaska. My heater leaked and was disconnected & I had no air installed. It was like sitting in a Sauna. So I pluged the great vents on the floor..added air conditioning & installed 2   7' spal fans right  behind the frt tires. These fans pull alot of heat out of the engine. Took a ride last Sat 93-95 degrees I was cool from the waist down & the engine never went over 195 degrees. Had to turn on the 16" spal puller at stop lights. Alot of fans going but I'm cool.

 Almost forgot I install the aluminium heat sheild too under the carpet

Alan

knotacare38530.5089699074

I have a 76 vette and having the same problem, this was covered in

 the interior forums back in early june, besides heat entering thru the

vents, guys have been insulating under the carpet, also the july issue

of corvette fever ahd a article about interior heat, I haven't tried to repair the problem yet

Also, check to see if your car still has the transmission tunnel heat barrier under the car, above the tranny.  There is also a tunnel foam block that goes over the tranny and forces the air deeper under the car as you are moving. 

[QUOTE=Mickey]Also, the amount of air that comes out is relative to the speed of the car.  At a standstill, the amount of hot air coming out of the ducts is very little.  At 60mph, the amount of hot air coming out of the ducts is roughly the equivalent of the fan being on med-high. 

This hot air ALWAYS comes out after the car warms up.  It does not matter what setting the controller is set on.[/QUOTE]

If this doesn't sound like my dilemma of a couple years back... I have a 73 with factory air. (Well, the factory A/C unit was there, forget the part about it possibly being cold or even cool  ).

And just like you when you would drive the car it didn't matter what setting the fan was on there was always hot air blowing out the vents. The faster the car went the faster the air blew.

You could turn the fan off, but get the car up to speed and it was like the fan was on medium speed, blowing nice hot air.

It took a couple years and a great deal of frustration, hot sweaty frustration from what I remember, but I finally found what it was.

The A/C evaporator housing (which is what you see in the engine compartment up against the firewall, that big kinda pointy box, wide at the firewall and narrows toward the front of the car, with A/C lines going into it from the compressor) is a two piece / 2 half / 2 sided design.

When you look down on the top of it you can see where the halves, or sides, seam together and you can see bolts that hold it together.

From the top and from the front it looked like the halves were perfectly sealed. And they were perfectly sealed.

But get under the car and look up at the halves. Mine had 1/2" gap all along the underside, the full length of the underside, that sometime in the past 30 years the seal went away. 

But the gap was enough to allow a pretty steady flow of hot engine air freshly heated off the exhaust manifold to enter into the ventilation system. The faster the car went the more hot air was flowing in.

I forget what I sealed it with. Being rather large I had to be creative. You can probably use duct tape temporarily.

Once I sealed it up there was no more free flowing hot air. I would have to use the fan to blow the hot air around.

Jump a couple years later to today... rather than attempt to repair the 30 year old system, I got an A/C / Heater system from Vintage Air. I have completely removed the entire stock air handling / heater / A/C unit and am in the process of completing the installation of the Vintage Air system. The nice thing about Vintage Air, it uses all the stock controls and vents and comes ready to bolt into a Vette.

In short, in my case the key was to get under the car and look at the bottom of the evaporator housing.

You might also check all the seals from underneath between the evaporator housing and the firewall, if any part of them is gone you are gonna get free flowing engine air into the car.

Hope that helps and good luck.  

 

 

 

What about installing a valve on the hot water hose? the
heating system on the corvettes seem to continuously cycle the
hot water past the heater core regardless if you have the heat
on or off. ive read some forums on this, and what is suggested
is that you install a hot water shut off valve on the heater hose
coming from the engine to the heater core. would cost about 2o
bucks using typical home depot hardware. in the summer shut
the valve, and the interior should be alot cooler.

heres the link i used to help me:


Off.shtml">http://temp.corvetteforum.net/c3/joeveto/Hot_Wate r_Shut-
Off.shtml

http://temp.corvetteforum.net/c3/joeveto/Hot_Water_Shut-Off. sh
tml

sorry if the link does not work, but its valid i know it works.

check to see if your hood weather strip is sealing at the firewall, take a piece of news paper and double or triple it and put it on the firewall lip that the WS sits, close the hood and see if you can pull it out, if it comes out easy then the weather strip might be dryed up or shrunk, engine heat will get into the plenum area through there, I also sealed off the fender channels on each side where the hood WS stops.   

heres the link i tried to post-

http://temp.corvetteforum.net/c3/joeveto/Hot_Water_Shut-Off. shtml


see if that helps-
ive installed one on mine, and it has reduced the inside temp big time!

Your definitely not alone Mickey. I have the exact problem and have tried all the fixes except the one above with the a/c evaporator housing. JEEZ it would be great to find one that actually worked. I'll just keep reading and trying. Anyone else found a fix? I'll try it too. My wife and I drove it the fourth to a party about 40 miles away. High 90's..even with the top off and rear window out, we cooked. It was worth the attention we got there though. Someday it'll be cool....someday