Hot passenger compartment
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
Hot passenger compartment
Hopefully someone has an answer. I just restored the interior in my C3, 1977/ 4 speed. I went through all the seals on and inside the heater box replaced them with foam seals. I made sure the doors worked properly and everything moved freely. Even after reinstalling I checked everything to make sure it was working properly. Now, when I drive the Vette you can feel the hot air rushing in through the lower vents on the driver and passenger sides behind, the center console. When I come to a stop the hot air seems to stop coming out. Is there any way to stop this? I know the C3 does get hot inside but this was like driving with the heat on.
I have replaced everything, original engine L48 bored 30 over with vortec 2.02 heads and a blue racer cam. Edelbrock intake with a Jett stage 3 carb. All hoses, heater control valve radiator all have been replaced. It is a 4 speed car with the factory 3.70's still in the rear. She runs at right around 190 degrees and sometimes goes to 205 while driving on the highway and sitting in traffic.
Any help would be greatly appreciated, Bill
I have replaced everything, original engine L48 bored 30 over with vortec 2.02 heads and a blue racer cam. Edelbrock intake with a Jett stage 3 carb. All hoses, heater control valve radiator all have been replaced. It is a 4 speed car with the factory 3.70's still in the rear. She runs at right around 190 degrees and sometimes goes to 205 while driving on the highway and sitting in traffic.
Any help would be greatly appreciated, Bill
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Older AC C3's, but I don't know when they quit putting them on. Stuff them with some foam. What did you do to mitigate the heat coming thru the floor/firewall before putting it all back together??
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
I used what looked like foil with insulation on it..then I put the carpet down on top of that. I went as far up the firewall as possible. Would it help if I took a pic of the vents so you can see which ones Im talking about? I really appreciate the help. Here is a pic of the vent (drivers side).
Last edited by HT1663WB; Aug 31, 2007 at 02:38 PM. Reason: vent
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
Just went through this on my 81. First thing to do is go buy a A/C thermometer and any part store. Get a temp reading on the upper vents above radio. compare that temp to outside air. Then I will post some pics of wehat I did. Does the A/C work ? if so, turn it on and open the hood. Feel for cool air in the engine compartment. If you have that, then hot air is coming in from the engine.
Let me know.
Let me know.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
A/C does not work. There is no air coming out of the top center vents unless I use the controls. THe hot air is coming from the lower vents with controls off as you're driving down the street. Is this the same problem you were having?
Thanks, Bill
Thanks, Bill
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Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
I used what looked like foil with insulation on it..then I put the carpet down on top of that. I went as far up the firewall as possible. Would it help if I took a pic of the vents so you can see which ones Im talking about? I really appreciate the help. Here is a pic of the vent (drivers side).
On my 68 those are the heater outlets. There is a vacuum operated door behind these vents between the firewall and the air boxs. maybe this hose came off when messing with the other vents.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
Thanks, Bill
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
If you mean the vacuum line, on my air car the line goes to the switchs on the consual. If you have a vacuum pump such as a "mighty Vac" you could pull a vacuum on the line to the door and see if it will hold and at the same time listen for the movement of the door. On mine the vacuum pot was leaking and would not close the door all the way and let hot air in the cabin.
Instructor
Joined: Jul 2007
Posts: 228
Likes: 0
From: Price Utah
heater control valve
I know you said you replaced the heater control valve but is it really shutting off the water. I ran constant vacuum to mine to shut it off and no more hot air from those vents. Mine was doing the same thing because
of low or inconsistent vacuum to the valve (80 Vette).
of low or inconsistent vacuum to the valve (80 Vette).
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
When you move the heater controls to defrost does the air come out of the defroster vents. If not, you have other problems but you are still sucking air from the engine compartment. In the morning I am sure you get cool air at the lower vent. As the motor heat up, here comes the hot air.
First thin make sure you have a new hood seal. Then there is a product that 3M makes. I call it dum dum but it is in a blue box about $20.00 a box and you can get at any parts store that carries body shop products. Place dum dum around the outer area of the heater box. Where the box attaches to the body. Do the same where the heater motor attaches to the heater box. I will post a pic later tonight.
First thin make sure you have a new hood seal. Then there is a product that 3M makes. I call it dum dum but it is in a blue box about $20.00 a box and you can get at any parts store that carries body shop products. Place dum dum around the outer area of the heater box. Where the box attaches to the body. Do the same where the heater motor attaches to the heater box. I will post a pic later tonight.
Last edited by spedaleden; Aug 31, 2007 at 08:32 PM.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
I just ordered the hood seal and I'll check on the other stuff in the AM. Yes the heat comes through the defroster when I move the controls to defrost. I found a before pic of the interior.
Last edited by HT1663WB; Aug 31, 2007 at 10:12 PM. Reason: answer
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
Here are some pics
Here you see the black dum dum on the seam of the air conditioner housing where the right and left sides meet. I had air comming out of there. When the air was on, I could feel cold air, but when on vent I was getting 90 degree air in the car.
Here is a pic of the bottom of the housing you can see the dum dum again that I sealed it with. This product never gets hard, it's like tar but never leaves a resudue on you. It stays plyable.
I did a frame on on this car and also replace heater core and all seals and gaskets. Now if the temp outside is 78 degrees, I get 78 degrees out of the vents. Make sure all of your vacumm doors are working properly. Seal around anything entering or exiting the heater box.
Here you see the black dum dum on the seam of the air conditioner housing where the right and left sides meet. I had air comming out of there. When the air was on, I could feel cold air, but when on vent I was getting 90 degree air in the car.
Here is a pic of the bottom of the housing you can see the dum dum again that I sealed it with. This product never gets hard, it's like tar but never leaves a resudue on you. It stays plyable.
I did a frame on on this car and also replace heater core and all seals and gaskets. Now if the temp outside is 78 degrees, I get 78 degrees out of the vents. Make sure all of your vacumm doors are working properly. Seal around anything entering or exiting the heater box.
Last edited by spedaleden; Sep 1, 2007 at 12:26 AM.
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
I have seen a lot of guys adding shut offs because they think the heater valve is not closing. As long as your getting vacuum out of the line. 9 out of 10 hot air from the engine is entering the A/C & heater box.
Burning Brakes
Joined: Aug 2005
Posts: 1,126
Likes: 0
From: Hudson Falls, N.Y. 76 Vette Modified L-48
your heat is coming from 2 places...the fender to body seals dry and fall away, and the heat from the engine comes thru the passenger vent, here's a pic, in yellow, where your seals are gone:
I used 2 inch styrofoam cut to fit the vent hole perfect, and coax dope, black sticky putty, to seal around the foam...
second, heat is coming thru the heater core, heat on or off, I installed a shutoff valve on the core input flow hose...
My car was unbareable before these modes....nice and cool now
I used 2 inch styrofoam cut to fit the vent hole perfect, and coax dope, black sticky putty, to seal around the foam...
second, heat is coming thru the heater core, heat on or off, I installed a shutoff valve on the core input flow hose...
My car was unbareable before these modes....nice and cool now
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
The rear hood seal is very important. My '76 air was not cooling properly and I put a thermometer in the vent with the a/c OFF. When driving with the car fully warmed up, the temp at the vent was close to 100 with the ambient temp around 75. I then replaced the rear hood seal and went for another drive. Temp at the vent was 75. My a/c problem was resolved with temp at the vent with a/c ON was 40. This is a generally overlooked area. I've heard so many guys complain about C3 a/c when I bet a lot of times this is the problem.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Originally Posted by Manuel Azevedo
On my 68 those are the heater outlets. ...
The blower not have an OFF.
Low Speed change to Off
Disconnect connector at resistor box under hood pass. side near high blower relay & bend down the connector to dk. brown wire & reconnect.
I have A/C. After above, something else you might try is changing the position to Vent or Max.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 2,297
Likes: 156
From: Clayton New Jersey
Here are some pics
Here you see the black dum dum on the seam of the air conditioner housing where the right and left sides meet. I had air comming out of there. When the air was on, I could feel cold air, but when on vent I was getting 90 degree air in the car.
Here is a pic of the bottom of the housing you can see the dum dum again that I sealed it with. This product never gets hard, it's like tar but never leaves a resudue on you. It stays plyable.
I did a frame on on this car and also replace heater core and all seals and gaskets. Now if the temp outside is 78 degrees, I get 78 degrees out of the vents. Make sure all of your vacumm doors are working properly. Seal around anything entering or exiting the heater box.
Here you see the black dum dum on the seam of the air conditioner housing where the right and left sides meet. I had air comming out of there. When the air was on, I could feel cold air, but when on vent I was getting 90 degree air in the car.
Here is a pic of the bottom of the housing you can see the dum dum again that I sealed it with. This product never gets hard, it's like tar but never leaves a resudue on you. It stays plyable.
I did a frame on on this car and also replace heater core and all seals and gaskets. Now if the temp outside is 78 degrees, I get 78 degrees out of the vents. Make sure all of your vacumm doors are working properly. Seal around anything entering or exiting the heater box.
Ok, I checked the A/C housing and found 95% of the sealer is missing. It's only intact along the bottom. Also where the lines come out of the box, top and bottom, there is no insulation, nothing you can see right into the box. It looks like the box was split before and never resealed. The air only comes in the car from the lower vents when it is moving. Sitting still nothing comes out. All A/C and heater controls are off while this is happening. Would the box not being sealed cause that much air? All doors are working and vaccuum lines are in place. I ordered the hood seal and I'll get the dum dum tomorrow.