71SoCal

A while back I posted a thread about getting the heat out of my '71's interior. I received a lot of great input.

The interior of the car would get hot even on cool days, so I knew that I needed to find and block the heat that was getting into the car.

I decided to bypass the heater core by removing and plugging the hose in/outs at the manifold and water punp. That seemed to be the solution.

The interior stays cool much longer now, but it still eventually gets hot again. I've had both sides of the dash off, and couldn't find any obvious leaks at the firewall. Is it possible that hot air is coming in through the heater core plenum?

The floor of the car is well insulated, but I do see some un-insulated firewall areas. Could that make a lot of heat?

My plan is to upgrade the blower motor to a C4 type, and my a/c does get really cold, but it seems so inefficient for the a/c system to have to fight all that heat.

Any idea would be greatly appreciated...

SLVRSHRK

Have you checked the passenger side vent. I read an article the other night in Corvette Fever about the seals being the cause for heat getting into the cabin.

Apparently, the plenum used by the vent is made from the outer wall of the fender and some side walls. If the seal between the engine side of the firewall and the outer fender is broken/leaking, hot air from the engine compartment will leak right into the system and your A/C can't keep up.

You can see the seam if you remove the vent door and look into the vent from the driver's side.

Could be one thing to check.

fugawi

is your tunnel insulation in place, and tunnel collar. when i replaced mine it cooled the interior by 20 degrees..

Sharky Guam

Yep, that is it...I have worked on many a vette with great air con but still not comfortable in the passenger cabin. I found out, that hot air was leaking in and bringing temperatures up.

Hwy St*r

Are later C3's (1978) the same. I get a lot of heat in mine also. How do you fix if the seal for the PS vent is a problem? Does anyone have pics of what to look for?

Thanx, -Pete.

KEEP DRIVING!!!

SLVRSHRK

Mine is a 78 and it is the same. The article is in the July 2005 Corvette Fever. They have some nice pics to illustrate.

mapman

What is the condition of the hood seal? Open the hood, put a sheet of paper over the top of the firewall, close the hood, and see if you can pull the paper out. (Check several places along the firewall.)

If NO resistence is met, then hot air from the engine compartment is escaping past the hood seal and now is free to enter the air intake for the heater/AC.

rihwoods

Used my mini-temp IR gun while driving to check pass side floor temps....it was 90 degrees ambient outside that day...got 127 degrees where my wife's feet rest on floor (at incline)..console side was 108 degrees....have 2-1-2 exhaust which runs down her side...
I plan to seal inside of pass vent as mentioned.......will experiment with various kinds of under carpet insulation on her side.....will add new tunnel insulation (last) at tranny...hood seal ok..

plan to re-take temps after each "fix"....

71406

On my 71 I've taken all the steps mentioned above, but my feet would still cook with the ac on. But I now keep my ac set on BILEVEL (instead of MAX) so that cool air comes out on the floor as well as the dash. No more hot feet and the car is comfortable to drive.

A78Corvette

This may not help you if you have to pass inspections, but I bought Hooker headers treated by Jet Hot. I ran 2 1/2 true duals to the mufflers. It helped the cabin temp. in my car. Just a thought it might help you.

Brettmc

Reach down and feel the vent outlet while driving. If hot air is coming out then there's your problem....

Brett

71SoCal

Awesome suggestions!!! This weekend I'm going to start debugging this problem.

I did check my hood seal and it is completely shot. But last year I pinned the fresh air flapper on the plenum closed, so I don't think any cowling air should be getting in through there???

I'd love to get one of those IR guns...where and how much???

The first thing I'm going to check is the passenger-side vent for air flow.

I'll post findings/results this weekend...

Thanks.

rihwoods

I bought a Raytek Mimi-temp Mt-4..$89.00...there are cheaper ones...like Harbor Freight..but this one was recomended by Dewitts..

Xakk

I pulled the plug off of the blower moter on my 81. Even with the heater core bypassed, it was still blowing hot air, and my vents are in such miserable condition right now, that it all blew straight down on my feet.

steves_77vette

One of the common mis-conceptions about insulation is where to put it. Putting insulation INSIDE the cabin is not going to help all that much. The reason is that the heat transfer is still getting into the cabin but is blocked from direct transfer where the insulation covers. The heat is still in the cabin and will go somewhere where the insulation ends. If you have heat coming in from the engine compartment or the exhaust, you have to block it from the OUTISDE before it even gets to the underbody. Themotec makes an aluminum sheet insulation with an adhesive back that should do the trick on the under body below the seats on both sides.

flynhi

In 69, GM installed heat deflector plates that mounted on the engine side of the firewall on the footrest incline. Install these in addition to the Thermotec and your feet will cool off.
The foam collar that wedges between the bell housing and the trans tunnel also has a huge heat reduction.
Also check the boots where the clutch and accel rods go thru the firewall and the grommets where wires and speedo and tach cables go thru.

Two ways to check for holes in firewall:
1. place a drop light in the footwell, turn out the lights and look at the engine side of the firewall.
2. Have a friend blow compressed air all around the engine side of the firewall while you feel for air on the passenger side.
Each approach found a hole for me.

rtpilot

ESU

Where exactly are these side vents you guys are mentioning? I'd like to check mine also . Are they behind the kick panels on the side of the front floor board? I thought I remember seeing a vent on the passenger side when I was re-installing the carpet.
Also I've seen some posts about installing a C4 blower motor, whats the purpose for this and what benefit is there?

ESU in NY

flynhi

The vent being described is in the right kick panel forward of the lower right speaker.

I installed the c4 fan and didn't get much improvement over a late model C3 fan. Early C3 fan had a fairly flat fan blade. Late C3 fan blades have more curvature. C4 fans have even more curvature but are about 3/4" longer and require a spacer to install.

Install a new motor with late C3 fan, make sure you have very good connections to the motor so that it gets a full 12v and you have maxed out the fan side.

Then work on the duct side. Start with the evap housing. Odds are it is partially blocked with leaves and debris. Connect a 1" +/- hose to the end of your shop vac and snake it down the fresh air vent at the outside of the passenger side cowl. Slowly snake it down and you will probably pick up mucho crap. This will unblock the evap core.

Remove the passenger side lower dash, turn the AC fan on high and feel around for duct leaks. Seal them with metal duct tape (not the el cheapo gray fabric type). This will put the available air in your face, not behind the dash.

Go to a plumbing supply house and get two ball valves to manually cut off the hot water coming into the heater core. This will keep hot water out of the cabin during warmer weather.

See corvettefaq for numberous articles on ACs

SkunkApe

Good advice above. However, only one ball valve is needed (top hose).