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Discussion Starter #1
Okay, its getting warm now and my 1979 vette ( without AC..hoses are ther just no compressor) is making me sweat even with the tops off. I would like someone to tell me just where the "fresh air" enters into the corvette. My AIM talks about cowl plenum but I just can figure out how air get into the ductwork behind the dash. No problem getting heat and when the car is sitting still with the heat control on "heater" but temp set to "cold" there is axctually "cool air " coming out at the feet area from transmission hump vents. There seems to be a vent door operated by a vacccum diaghram( but doesn't work...even if it did I think it only recirculates inside air)
If I new how the outside air got into the system I could check to see if it is blocked. When I switch temp setting to "hot" wow it burns you up. I just thought the "cold " should be colder than it is.
Any help would be apprecited( especially before I head the beach)

Marc
 

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Mark, there should be a vent position on the center consol. This lets outside air into the car. Mine works fine now that I've shut off the water supply to the heater core. It just take a valve in the line going to the heater. Hope this helps a little.

Dave
 

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Dave:
Thanks for the reply. I actually thought about doing that myself but doesn't pressure build up in that line if you have the valve closed off? I thought the water circled thru the heat exchanger in the heater then came out and went back to engine. If you put a shut=off valve in there, where does the water go? I'm still curious as to how the outside air physically enters the ductwork in the dash!

Marc
 

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A lot of cars have a valve in the input side of the heater to turn of hot water to the heater, most are cable controlled......so I don't see there would be a problem doing it. my Toyota Hilux has this system.

can't help with the air though........my vette was converted pretty dodgy, alot of it is missing under there and has a mazda heater of all things!
 

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DC Crew
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Check out the new SURE FIT a/c system from Vintage Air. It won't only solve your problem, but it will create tons of extra space on your firewall (making it easier to change those rear plugs), and cost about what it would take to re-vamp your current stuff. The entire system is under $1,500 including what you would need to pay a shop to evac and charge it.

It is computer controlled and won't let the hot water mix in when you don't want it - and works like a modern a/c system with electric servos. It replaces your entire system less the vents and control head.

Before they made this, I custom mounted a Vintage Air Compact Super Cooler II into my 69 Vette. It cools like a champ. I installed a SURE FIT this last fall in a C3. It had a few bugs in it, but once they were squared away, it kicks major cool butt.

Comparing, I totally redid a stock 71 a/c system this last Winter - all new seals, hoses, parts - pieces. Yes...it cooled, but didn't/doesn't come close to what the aftermarket unit can do.
 

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Mark, I've never had an overheating problem with the valve installed. We used them at work for years to keep the trucks cooler.As for air circulation and heat in the summer, these cars are just HOT without a/c. I've even put extra heat barrier under the rugs. That helps some what.

Dave
 

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Go to any auto parts store and get one of those plastic heater hose adapters that will allow you to plug the heater imput into the heater output. This allows the coolant to flow, but just not in the core. There cheap, and come winter you can just re-rout the hoses.

Dude
 

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correct me if im wrong but my 79 has a vacuum operated valve that opens and closes depending on the setting inside. but im startin to think mine is shot because when i drive with no a/c, it gets hot sometimes underneath the dash. and i dunt think it is the heat from the engine.
 

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DC Crew
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Dave:
... doesn't pressure build up in that line if you have the valve closed off? I thought the water circled thru the heat exchanger in the heater then came out and went back to engine. If you put a shut=off valve in there, where does the water go?

Marc
The cooling system isn't a "positive displacement" system. That means it can "dead head" at a valve with no circulation and not hurt anything, it just re-routes the water elsewhere.

As far as your problem goes, the air is picked up from the side cowls on each side of the inside fender in front. With your hood open, you will see a screen or grill (unless it has been removed :)) on the pass. side just after the airdam of the rear hood seal (what? :laughing: ). The air is picked up at the high pressure area at the windshield and drawn into the cabin by the fan.

A lot of times, hot air finds its way into the cabin from the engine compartment. :thumbsup:

I will try to find pictures ..... :huh:
 

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Discussion Starter #10
Thanks to everyone for your input. I now understand where the outside air is pulled from.
Joetape650, I think you are right. Ther is a vaccum diaphgram near where the two water hoses enter the heater unit at the firewall. I have no vaccum on this ( even if I did , it may be broken. ) Can anyone confirm if this does acccuate a shut oof valve?

Thanks
Marc
 

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Yes that diaphram opens and closes the flow of coolant, and there should be a very small diameter hard plastic vacuum hose that feeds it.
 

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shut off valve

you can buy a shut valve and install it on the inlet side heater hose that is what my 79 has when i don't want heat i just pop the hood and shut it off if it gets cool out just turn it back on. no need to worry about a vacum valve working or not (just my 2cents) good luck with which ever route you take:thumbsup:
 

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I installed cutoffs on both heater hoses on my 79. This keeps residual heat from coning back into the heater core. The only time the heat is completely cut off on C3s with A/C is when the A/C is set for max cold. Even then the old shutoff valves did not work properly. Installing a shutoff contol on each hose is the only way to completely stop hot coolant from entering the heater core and they cause no problems to the cooling system.
Bernie
 

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...Ther is a vaccum diaphgram near where the two water hoses enter the heater unit at the firewall. I have no vaccum on this ( even if I did , it may be broken. ) Can anyone confirm if this does acccuate a shut oof valve?...
Sounds like the shut off valve, but a pic would confirm it. Most (but not all) are mounted on the right fender skirt. You should also find a nipple on the valve (usually on the top) for a small vacuum line. Somewhere under your hood is the line. Console AC controls send a vacuum signal to the valve telling it to either open or close. If the valve is stuck in the open position or if it is not receivng a vacuum signal to close, hot water is running through the heat/defrost core all the time.

Get the AIM. AIM shows the various vacuum hose routings you're looking for and includes the color code (stripe) for the hose to the valve.

Ditto on the flapper door at the cowl. It has a color coded vacuum line too.

:thumbsup:
 

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Hot cabin

After dark, set a light shining towards firewall (under dash)from inside vette...then look from engine side to see if any light leaks through...each opening is another source of heat....;)

Rich
 
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