heating problem
 

hey guys whats up?
I have a 1974 sting ray, and I have a problem with the heating and controls. when the car is sitting still the heat will only blow out of the defront, now matter were the control is set, (on vent or on cold).
if the car is moving, cold air comes from all the vents even if its on hot, cold, on defrost, or if the fan is off. makes it kind of cold driving in the winter! I'm guessing its a vacuum problem sents it seems like everything on the car is run by vacuum.
any help would be great.

Welcome to the Corvette Forum. Defrost is the default position of the divertor door when no vacuum is applied. Sort of a safety feature since in the winter it's better to be able to see where you're going than have warm feet. Will have to troubleshoot the vacuum system.

Here's a diagram, this might help you find the problem, PG.

hey thanks for the info and the pictures, this should help a bit. what is the best way to get to the lines? just take out the console, or is there a
specific part that tends to go bad? I have not done a lot of work on this car so I'm kind of new to its problems. just bought it last year.

Heater Headache!
 

In the first diagram you see a line called "To Vacuum Supply Source" lets see if that is connected, to do that:
Remove the air cleaner and look on the intake manifold just behind the carb, there is a fitting screwed into the manifold, that is where all the vacuum starts from. Follow those lines around, you should find 1 that has a "T" and goes thru the fire wall. That is the one that must be connected to "Vacuum Supply Source" in the diagram.
Hope that helps.
You should fill out your profile, is your Vette auto or stick, have A/C or not?
PG.

This is how it is on a 79:
Where it says to vac supply source, it goes through the firewall on the passenger side behind the dist. It connects to a junction (looks like a tree) right behind the glove box, just remove the inside of the glove box to get to it. On the diagram you see a cirlce with blue red tan and pink going to it, this is under the center councel below the contols. I pulled the dash and center to council to figure all this out and found out that the hoses from behind the glove box to the engine were rotten and just fell apart in my hands. You can get the hose at any auto parts store.

Do you have a cut off for the coolant going to your heater core? It would be a 3/4 inch hose coming out of the front top of the engine, a shut off valve, and then going down to the passenger side fire wall and connecting to a valve down there above the tire (a small vacuum hose will also come out of that valve. Open it in the winter to stay warm and turn it off in the summer to cut the heat coming into the compartment. Trust me, you will see the difference.

my car does not have a shut off valve on the hose, I looked for that first, I was hoping it would be that easy, no such luck.
I have taken about all of the inside of the car apart now, dash pad, council, passenger and middle dash. the supply source hose looks fine, I have followed it from one end to the other. the other hoses look good to, I'm thinking they may have been replaced at one time. the only one I did not follow all the way was the rear vent vacuum valve hose, I did notice that were it turns into a steel line it is rusted some what. also the drivers side headlight does not lock, and it takes it a long to rise fully, could this be linked in any way.

Recommend getting a Mityvac to use to isolate where the leak is.

Hi again, you need a shut off valve to stop the hot water from circulating thru the heater core. Advance has it but it's listed for a 79, none are listed for a 74. The black hose coming from the left side of the picture is the vacuum hose that connects to the correct valve. When you turn the thumb wheel on the console it applys vacuum and that opens the valve to let the water circulate.
I put in a ball valve and pluged the vacuum hose. PG.