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CorvettesCockpit
Heat - I may be on to something here

vettfixr
Senior
Member

1967 posts [100%]
Sewell NJ

Cockpit Heat - I
may be on to something here

5:07
AM 8/12/2002

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 cault 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.

[Modified by vettfixr, 8:11 AM
8/12/2002]
_______

Knowledge gained and not
shared, is knowledge lost.

vettfixr
74 L-48 T-Top
More Enhancements
than Pamela Anderson Lee
5 Coats DuPont Diamond Black
Acrylic Lacquer
5 Coats DuPont 380-S clear Acrylic
Lacquer
Sewell,NJ
Vettfixr's Website

Black Sheep Squadron

flynhi
Senior
Member

1965
posts [100%]
Austin TX

Re: Cockpit Heat -
I may be on to something here (vettfixr)

5:31
AM 8/12/2002

Excellen t tip. In 15 years of dealing with C3
cockpit heat, I've never heard or thought of this
one......
_______

"Every true and precious thing
worth having stands on the razor's edge of being lost and must
be fought for"
71 Black on red Conv, Lingenfelter 383, 44mm
runner tpi, 52mm TB, 24# injectors,custom chip,409 BHP, 509
BTRQ, Muncie 4sp, 3.55, coated headers, mandrel pipes w/ x
crossover, 1 1/8 front, 5/8 rear stabar, fiberglass springs
front and rear, Bilsteins, 80 seats

AlwaysWave
Chicago Events Coordinator
Cruise-In III
Veteran

4195 posts [100%]
Member since Feb. 99

Re: Cockpit Heat -
I may be on to something here (vettfixr)

5:53
AM 8/12/2002

Excellent tip I've done the insulation and the water
shut off just as you have. I have noticed on my 72 that when
driving I can reach down and feel the hot air movement, but
when at a stop light I can't. You may have given us the
answer.

Another thing as a just in case. Where can I find the wire
to the heater blower motor? I'd like to splice in a manual
on/off toggle switch there.
_______

Stars &
Stripes Tour wrap up, not complete yet ==> http://temp.corvetteforum.net/c3/roadfever/index.shtml

81vette
Senior
Member

290
posts [100%]
Humble Texas

Re: Cockpit Heat -
I may be on to something here (vettfixr)

6:01
AM 8/12/2002

Good tip. Thanks!

Mark
_______

1981 Red/Red.
350 SB, 4 speed, 2.72 gear, 3020
lbs. with 1/2 tank
VBP Street/Slalom Suspension
System.
VBP Stainless Steel Brakes.

Coming soon...
415 SB, 5 speed TKO, 2.72 gear, with est.
weight of 2775 lbs.

vettfixr
Senior
Member

1967 posts [100%]
Sewell NJ

Re: Cockpit Heat -
I may be on to something here (AlwaysWave)

6:39
AM 8/12/2002

Probably the easiest way to put in a toggle
switch without having to cut your wiring harness is to install
it in line at the blower motor. The connector to the blower
motor is just a spade connector. Unplug it at the blower motor
and plug a male spade connector to the harness part. Run this
line to a toggle switch and then run a line from the toggle to
a female spade connector that you will plug into the blower
motor. Then if you ever want to remove the toggle you just
plug the original harness back in to the blower motor. This
will stop the blower motor from running but probably won't
stop the heat from coming out of the vents. Once you're
underway the movement of the car will allow air into the
heating and AC system because of pressure. If you have leaks
like I did this hot air will still enter the system and come
out of the vents.

vettery
Junior
Member

17
posts [100%]
Lonoke Arkansas

Re: Cockpit Heat -
I may be on to something here (vettfixr)

10:11
AM 8/12/2002

I discoved that source of hot air too, but in
my case is was after I removed the right front fender. It
wasn't bonded completly to the front of the
plenum.
_______

Vettery

'79, L82, 4-speed

vettesite
Senior
Member

648 posts [100%]
Palatine IL

Re: Cockpit Heat -
I may be on to something here (vettfixr)

11:15
AM 8/12/2002

Thanks for the tip!!!

I'll have to check this out. I hope the cooling system on
my '80 is similar to the '74, I think it
is.
_______

1980 L-82 restoration web site

1980 L-82 black/oyster | 355ci small block decked (#'s
kept), balanced & blue printed | TRW cast flat top pistons
.030 oversized | Stock heads milled, pocket ported, polished,
gasket matched, multi angle valve cut | PBM SS valves 2.02
& 1.60 | Edelbrock Performer EGR Intake #3701 | Comp Cams
CS 268h-10 single pattern cam (110 degree lobe separation,
218/218 @ .050, 268/268 @ .006, .454/.454 valve lift),
lifters, valve springs & double roller timing chain kit
#K12-210-2 | Edelbrock 795 cfm performer Q-jet carb #1904 |
Pro Flow 360 degree air cleaner #1207 with 14" K&N filter|
Custom 2.5" dual exhaust with Flowmaster 40 Series Delta Flow
mufflers #942541, no cats, H pipe, & Blackjack headers |
Rebuilt Turbo 350 trans with a B&M Transpak set to Street
| Rebuilt Dana 36/44 rear end with 3.55:1 ring & pinion |
BF Goodrich P255 60 R15 tires | KYB GR-2 silver front &
rear shocks | Vette Brakes fiberglass rear spring and front
& rear suspension | A/C 134a |

Fast Glass Whiplash!

wellsw
Senior
Member

26
posts [100%]
Palm Springs, CA USA

Re: Cockpit Heat -
I may be on to something here (vettfixr)

7:17
PM 8/12/2002

Hi, This sounds like a great tip, however my
problem is I don't understand what the plenum is. I am
starting a project to replace my heater core and install new
carpet, so it would seem a good time to do the seal you talk
about. Is there another name for the plenum, or is it referred
to as something else in other parts of the manual? Thanks,
Wells

74-Roadster
Senior
Member

956 posts [100%]
Fort Worth TX

Re: Cockpit Heat -
I may be on to something here (vettfixr)

8:58
PM 8/12/2002

Thanks for the tip!!!!!!

But I'm not sure what part wasn't sealed against what part.
Are you referring to the heater core box (plenum) and where it
seals against the firewall?
_______

I just love
Hooters

1974 two top car, L48, AC, PS/PB, TT & some
temporary wheels, lots to come . . . Stay tuned!!

We can customize her, we have the technology. .
.

Chris81
Senior
Member

586 posts [100%]
Garner NC

Re: Cockpit Heat -
I may be on to something here (vettfixr)

10:35
PM 8/12/2002

another something added to my
list...
_______

ZZ4, 700r4, 3.54s
17x8" TT II's, 255/50 Nitto 450's

Carolina C3 Corvettes

My CorvetteForum Page

LT1driver
Senior
Member

916 posts [100%]
West Texas

Re: Cockpit Heat -
I may be on to something here (vettfixr)

10:49
PM 8/12/2002

That is great info. I am going to check mine
this weekend. Thanks for the tip.
_______

LT1driver
1970 LT-1,
Stock

vettfixr
Senior
Member

1967 posts [100%]
Sewell NJ

Re: Cockpit Heat -
I may be on to something here (74-Roadster)

3:21
AM 8/13/2002

No, the heater core box can be removed from the
car for rebuilding and resealing. The part I'm talking about
is the plenum that the heater box seals against and draws
fresh or recirculated air from. This part is behind the right
front fender and can only be reached by removing the fender.
You can get to the seams by going in through the flapper door
on the right side kick
panel.

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